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askscience
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The mass defect is the difference between the actual mass of the nucleus, and the mass of Z isolated protons plus N isolated neutrons.
The mass excess is the difference between the actual mass of the atom, and A atomic mass units.
Typically everything is calculated in terms of atomic rather than nuclear masses (so electrons are included), but the contributions from the electrons are often cancelled out when you take differences, and contributions due to electronic binding energies are on the order of eV, so they’re often neglected.
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askscience
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The pressure differential between the ISS and the vacuum of space, as well as the size of the hole are all factors to consider.
What you see in the movies with massive decompression due to a small, even moderately sized hole, are pretty much fiction.
Fill a balloon with water and poke a hole in it with a needle and you'll get a sense for why it took so long for the air to escape from the ISS.
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askscience
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Heck, take two balloons filled with air, poke one down where the rubber is thick around nozzle and the other in the main body of the balloon. On the one where the rubber is thicker the balloon will slowly deflate, while on the other the escaping air through the stretched balloon will cause the hole to tear itself bigger until it's big enough for the air to all escape quickly.
The size of the hole is only as important as the strength of the material the hole is in. This hole was drilled through metal so the metal wasn't going anywhere to allow the hole to expand (that said, I doubt there'd be much of the ISS's inner surfaces that'd be thin and flimsy enough to rupture from the air like a balloon skin, even if the pressure was higher inside)
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askscience
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The hole was roughly 2x2mm. A portal-type door is roughly 24x48 inches. Iirc, they said it would take a week to evacuate the station of air with the small hole. Given that timeline, the ratio of the surface areas of the two holes, and the number of seconds in a week, also assuming the two volumes are equal, a door-sized hole would evacuate in about 9 seconds. Does that track with what you saw in the movie?
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askscience
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> Fill a balloon with water and poke a hole in it with a needle and you'll get a sense for why it took so long for the air to escape from the ISS.
But how much pressure is in a water balloon? Better fill an old bicycle tire up to 1 bar and poke a needle through it. It takes quite some time for it to leak out. You can even calculate the air volume and compare it to the ISS.
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askscience
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The pressure difference between inside and outside the space station is only one atmosphere. That's comparable to the pressure difference for a submarine under 10 meters of water. You wouldn't expect a 2 mm hole in the side of a submarine 10 m under water to cause rapid, catastrophic flooding either.
[Here](https://en.wikipedia.org/wiki/Byford_Dolphin#Diving_bell_accident) is a somewhat famous example of a catastrophic decompression accident involving a 9 atmosphere pressure difference, and also a larger hole.
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askscience
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Fun fact: the watches astronauts wore on the moon (Mostly Omega Speedmasters, one experimental Bulova watch) were basically just strapped around the wrist of the space suit with a cushioned Velcro patch over them to prevent damage. This is because the pressure differential between atmospheric pressure and space is smaller than the pressures the watches were built to handle under water. Counterintuitively, a watch is actually under less stress in the vacuum of space than at ordinary SCUBA depths. Interestingly, there were a few instances of the crystals of watches popping out of the case because they are designed to resist pressure inward, rather than outward.
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askscience
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Yes it is, to quite a large degree. Geneticists know this in part through studies of twins: identical twins, who share 100% of their genetic variants, have more similar intelligence than fraternal twins who only share 50% of their genetic variants. Estimates of the heritablity of adult intelligence are in the range of 70 – 80%. This means that 70 – 80% of the variation in intelligence within a population is due to genetic differences. (See: https://en.wikipedia.org/wiki/Heritability_of_IQ#Estimates )
Researchers know intelligence is largely based on genetic factors, and are currently trying to identify which genes are most important. One of the most recent papers can be found here: https://www.nature.com/articles/s41588-018-0152-6
The abstract, for those interested:
>Intelligence is highly heritable and a major determinant of human health and well-being. Recent genome-wide meta-analyses have identified 24 genomic loci linked to variation in intelligence, but much about its genetic underpinnings remains to be discovered. Here, we present a large-scale genetic association study of intelligence (n = 269,867), identifying 205 associated genomic loci (190 new) and 1,016 genes (939 new) via positional mapping, expression quantitative trait locus (eQTL) mapping, chromatin interaction mapping, and gene-based association analysis. We find enrichment of genetic effects in conserved and coding regions and associations with 146 nonsynonymous exonic variants. Associated genes are strongly expressed in the brain, specifically in striatal medium spiny neurons and hippocampal pyramidal neurons. Gene set analyses implicate pathways related to nervous system development and synaptic structure. We confirm previous strong genetic correlations with multiple health-related outcomes, and Mendelian randomization analysis results suggest protective effects of intelligence for Alzheimer’s disease and ADHD and bidirectional causation with pleiotropic effects for schizophrenia. These results are a major step forward in understanding the neurobiology of cognitive function as well as genetically related neurological and psychiatric disorders.
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askscience
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In the most technical sense, no, the evidence does not seem to indicate that it is possible to make yourself more intelligent. However, your "general intelligence" is not the only thing that determines how well you can learn things. Having lots of background knowledge and diligently studying is important too.
Often, when a person rapidly learns a new subject, it's not just because they're intelligent, it's because they have lots of little tiny bits of knowledge that help them make sense of new knowledge. For example, if two English speakers are learning French, but one of them already knows Spanish or Italian, they're definitely going to learn French faster than the other person. The same thing applies to math, chemistry, you name it. The more you learn, the easier it is to learn more by relating it to things you already know.
I've encountered people who claimed to be "dumb" because they had trouble grasping some complex concepts, when in fact they were just missing the basic knowledge that was needed to understand.
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askscience
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That makes sense, it's like a foundation to build on.
how exactly would you be able to identify someone as more intelligent by their genetics? I'm a bit confused. If two people (one with the genes, one without) were put in a course in which they both had no background knowledge and they were given the same amount of time and materials to study, how would their performance differ? I'm not sure how intelligence is actually being measured here.
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askscience
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Measuring intelligence by how well a person does on any one specific task doesn't work very well, since lots of factors besides intelligence will affect their performance. We measure intelligence by testing people on a LOT of different types of problems (verbal comprehension / reasoning, logic, mathematical reasoning, spatial reasoning, etc.), so that we get an overall estimate of their learning / reasoning ability that is less affected by how experienced they are (or any specific deficits they have) in any one specific area.
This is related to how we know there actually is such a thing as general intelligence: If you take a million people, give them all a test with many different kinds of problems on it, and look at the results, you'll notice something: on average, people who get one kind of question right tend to get other kinds of questions right too. People who are good at spatial reasoning are, ON AVERAGE, better at verbal reasoning (and so on) too. The only way to explain that is that there must be some kind of general ability that people have, that is used for all different kinds of mental tasks to some degree. We call that general ability *g*, or "general intelligence." We can even mathematically estimate how much of someone's performance on a task is explained by *g*, and generally it's about 50%. So when it comes to solving difficult problems, your performance is about half due to your intelligence, and about half due to how diligently you work at it, how hard you study, how much relevant knowledge you've collected.
Note that testing someone's intelligence doesn't directly tell us if they have "smart genes." From other studies, we know intelligence is about 70-ish percent genetic, so if someone is especially smart (or dumb), all we can say is "it's probably about 70% due to your genes, and probably about 30% due to your upbringing / nutrition / education / etc."
Just knowing that our intelligence is heavily influenced by genes doesn't tell us which genes. There have been studies that compare the genomes of smart and less smart people, but that kind of thing is WAY harder than it sounds. Sometimes a trait is basically determined by one or two genes, like eye color, and it's super easy to figure out which genes. Intelligence is NOT like that. It's more like trying to figure out exactly what causes some states to have higher rates of smoking than others. So many things influence it, and some things might only affect that under certain circumstances... And that's basically what bioinformatics is about.
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askscience
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Just a warning. What you write, although well sourced, isn't universally accepted.
This book review gives a decent outline of the controversy in this field:
https://www.nytimes.com/2009/03/29/books/review/Holt-t.html
Also, an example of how these numbers get misinterpreted:
You might think that we could design a DNA test for babies and predict that one person will have an IQ of 120 and another 90. However, it's probably more like the DNA test will be inaccurate for everyone in the normal range, but can predict someone with Down's syndrome, who will score 40 on an IQ test, quite well. The outliers contribute a lot to the variance.
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askscience
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I believe the point of confusion is related to the wave and particle nature of the photons and how we choose which interpretation to deal with based on the situation. If you oscillate a bunch of charges at a low frequency you produce a radio wave, which are basically photons with very low frequency. The gif provided by noun_exchanger is similar to what happens when there is a change in current in a wire and an EMP is produced. What I think noun_exchanger wants to know is if it's possible to measure the time interval of this EMP on a quantum scale from a single charge.
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askscience
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This is much closer to what I'm getting at. Basically, it seems if you translate that mechanism of producing EM radiation as seen in the gif to a single charge going around and around in a circle pattern, it will be continuously oscillating the electromagnetic field (aka emitting waves). And from the little I understand about the discrete nature of photons, this can't be the case because photons are discrete chunks of energy, not continuous waves.
The follow-up questioning I had with /u/mfb- is basically: if the gif accurately represents how photons are produced, the wave can't be continuously emitted, they must be emitted in chunks and therefore possibly have time intervals between their emissions .. or else it's continuous. I don't really care WHEN the photons are emitted, I'm just looking for someone to confirm or deny that a finite amount of photons must be produced and the gif model is not entirely accurate at presenting how a single charge going around in a cyclotron emits energy. Either that, or I'm going mad trying to understand this stuff.
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askscience
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I'm not concerned with when or how many photons are being produced by a single electron circling around in a cyclotron, I just want to know if the gif is consistent with the photon nature of EM radiation. If the gif presented a single charge moving around in a circle geometry with this same wave-like EM emitting mechanism, it would be **continuously** emitting waves - which from what I understand about the discrete nature of photons - can't be the case. Photons are discrete energy chunks... and the gif would be presenting continuous oscillations in the EM field if it showed a charged accelerating around in a circle pattern. Is the gif an inaccurate way of viewing **discrete photon** emission, or did I am going mad here?
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askscience
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I'll just kind of copy paste a bit from my previous comment: I'm not concerned with when or how many photons are being produced by a single electron circling around in a cyclotron, I just want to know if the gif is consistent with the **photon nature** of EM radiation or if the gif is strictly showing some "classical" model of EM radiation that doesn't make sense to apply literally to photons.
If the gif showed an electron circling around in a cyclotron and it showed this same EM wave producing mechanism, it would be showing continuous waves being emitted... which seems to be inconsistent with **discrete photon** behavior.
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askscience
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Okay, I can accept that every moment in time contributes to photon emission, but ultimately I think my question had the most to do with viewing the gif as a complete picture of how photons are formed/emitted. /u/mofo69extreme indicated the gif only shows classical EM wave behavior, and does not attempt to visualize any quantum behavior associated with the discrete nature of photons. Is that an accurate statement in your opinion?
If the gif showed the charge in constant acceleration on a circular path, it would be creating continuous wave patterns in the surrounding EM field - which, in reality, is not the complete story. There is some discretized nature to the created EM waves that the gif is not showing, correct?
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askscience
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Yes I understand photons are oscillations in the electric/magnetic field, right? The gif is showing the propagation of a single wave in this field. Could the single wave not be considered a photon to some extent even with an ill-defined frequency?
My concern with the visualization in the gif is if we take the lone charge and make it continuously accelerate in a circular path. It would seem to be emitting continuous waves a la classical EM radiation, but really there is some other aspect to it that is more quantum in nature - and the gif seems to be missing something or is misleading if I'm trying to conceptualize the quantized nature of photons. I understand the electric field and the visualization is the original gif are a piece of the puzzle, but is it not an incomplete picture?
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askscience
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Well the simple answer is yes, if you take someone who has depression or whatever and run them under various diagnostic tools while they are ill and after therapy (or during drug treatment that is working) there are clear differences. The other posts show the topic as a whole is more complicated but the way I see it is you asked a direct question and the direct answer to it is yes, even if you need more context to really understand it. The hippocampus enlarges, the amygdala shrinks, you'll find alterations in connectivity e.g. the vmPFC-amygdala pathway etc.
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askscience
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Where do you read the requirement that the changes have to be the same for every patient? Why do we need to specify what the exact changes are? The question only asks if there *are* observable changes with recovery, which there obviously are unless you're suggesting depression has no physiological basis in the brain at all. Answering this question does not need us to be able to diagnose depression with an MRI, not even close. You're answering a totally different question to the OP.
You also didn't answer my question, simply repeated your answer.
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askscience
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> The hippocampus enlarges, the amygdala shrinks, you'll find alterations in connectivity e.g. the vmPFC-amygdala pathway etc.
Are there longitudinal studies that show changes in the volumes of these structures/tracts that change as a consequence of depression? Merely showing a difference between two groups is not the same as predicting a change in an individual.
If a group of patients with MDD has smaller amygdalae than a group of controls, this could have been a structural difference that is unrelated to MDD, or that is not causal of MDD but a consequence of some other process. It is plausible that remission of depression would not "reverse" the smaller amygdala.
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askscience
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>as the brain's structure is changing continuously.
You're not wrong, but you are grossly overexaggerating the degree of the daily changes within the brain that occur as a result of everyday life. The changes you're referring to are nowhere near the scale of the ones that are thought to occur in association with depression. Eating lunch is going to make you gain weight, but it is not going to add inches to your waistline.
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askscience
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> Are there longitudinal studies that show changes in the volumes of these structures/tracts that change as a consequence of depression? Merely showing a difference between two groups is not the same as predicting a change in an individual.
I was just giving examples of what might change off the top of my head. There are studies which clearly show changes particularly with successful antidepressant treatment. They compare endpoints, not populations. But since depression describes a set of symptoms rather than an etiology, the same changes will not be observed for everyone although changes *are* observed.
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4630287/ sums it up nicely.
> If a group of patients with MDD has smaller amygdalae than a group of controls, this could have been a structural difference that is unrelated to MDD, or that is not causal of MDD but a consequence of some other process. It is plausible that remission of depression would not "reverse" the smaller amygdala.
Okay but I'm not saying every single known physiological correlate/predisposition/consequence of depression is going to recover, as if it was never like that. So I'm not sure what you're getting at.
> There is no change, or cluster or changes, that you could claim as diagnostic of remission of depression.
> If you're going to say any change in brain structure is a change in depression then you're going to have a bad time, as the brain's structure is changing continuously.
Yes there is no cluster of physiological changes that can consistently be applied to everyone because depression is not a single disease. I'm not saying *any* change in brain structure must be related to changes in depression (given there is a clinical improvement) as we have research which shows what changes observed with treatment are specifically associated with improvement.
I was too quick to say "yes" when I should have said "yes, if you include connectivity and activation which are related but not the same" but your requirement to diagnose the presence or remission of depression physiologically is not strictly necessary because the question is about observing changes, not diagnosing static states of depressed and not depressed. If you could diagnose these states then yes you could compare them and say "these are the possible changes" but what I'm getting at is that you can also observe the changes through treatment as they happen without knowing beforehand which ones are actually contributing to depression. It can be done both ways.
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askscience
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This is super interesting! I found another higher tier paper supporting that one:
[http://www.pnas.org/content/early/2013/12/20/1321060111.short](http://www.pnas.org/content/early/2013/12/20/1321060111.short)
​
However, this has to do with testosterone levels, which is not the same that muscularity. And moreover, I didnt find any paper in which they actually measure the sickness frequency with testosterone levels. Given the inverse correlation with inmune response found in those 2 papers, we should expect that the frequency is higher, but we don't know if testosterone is having a protective effect through another pathway.
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askscience
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> I'm sure you can logic through a dozen reasons yourself why this is worthless to base an argument on
I don't see right now why is it so worthless, can you elaborate?
I mean, if you look through the history of art, it is clear that muscular men have been considered attractive for quite a long time now, I would say enough to allow natural selection.
And it makes sense that in more ancient times, being fit and muscular made more sense as a positive trait as it does now (because wars and manual labor were more common).
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askscience
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That sounds like a massive reach from the data. Lower CRP and WCC count does not necessarily mean impaired immunity in any meaningful sense, and in fact could be read the other way around - infections progress to a more severe stage in lower muscle mass patients requiring and causing higher levels of CRP/WCC. High CRP and WCC is strongly associated with mortality in infection, so it doesn't seem clear to me that high levels should be seen as a good thing, even if they are high for a purpose.
Unfortunately I don't seem to be able to get that abstract to see if the study design mitigates this at all.
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askscience
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ok, throwing out the quick obvious ones...
- throughout most of human existence, females have NOT been the ones picking mates, so what surveys of females currently show regarding male attractiveness has little weight in this argument
- in fact, (esp the european) humans are among the minority cases among mammals/animals where there is clear evidence males have been doing the picking, as several female phenotypes have clearly been selected for/against (e.g. enlarged breasts and buttocks, gender preferential paleness of skin (incl possibly hair and eyes as well), thorough suppression of female ovulation, progressive selection of neotenous characters for female 'beauty', 'feminity', voice etc... likely because human survival was so difficult, foraging males had such high mortality, and females/children were so often and so completey dependent on male provisioning, that males were in a position to select for desirable female characteristics for at least thousands of years, long enough for those male preferences to be conspicuous in female anatomy!
- further, even if you were to dwell on that, its obvious the bigger preference as seen in action vs what ppl say in surveys, is that the biggest bias on women's willingness to attach with males to create children/families is still on men's wealth/resource, which is turn is most correlated with intelligence and social abilities
- evolutionary timescale is in the tens of thousands to millions of years, and there we have pretty clear understanding of what exactly was most important to male success over this time, as you only have to look at what has been most strongly selected.. and those are straightforward.. more intelligence, better disease resistance, ability to digest more foods.. in summary, it has been a pure selection for survival, the pesky business of 'who do the ladies want' has been a far secondary concern
- further, survival for humans has most directly been predicated on food availability and needs, so 'muscles' are always in direct conflict with survivability across droughts, cold snaps, famines etc.. i.e select those who have the least necessary muscle mass to survive to keep food requirements low.. indeed when there's excess food, storing that as fats is a much more efficient use than making muscles, as any muscle mass actively needs to burn food all the time, which ofc helps us understand some of the 'why's behind the modern obeseity epidemic
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askscience
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That abstract seems **highly** questionable to me, as CRP and WBC are extremely nonspecific blood tests that can be elevated or suppressed for a lot of different reasons. Having a slightly lower WBC does not tell you anything about whether your immune system is stronger or weaker.
In order to prove that excess skeletal muscle mass suppresses immune system function, you would have to show evidence of increased infectious disease incidence, prevalence, or mortality in very muscular individuals. To my knowledge, there is no high quality evidence in humans that supports this.
Obesity correlates with a [significantly increased risk](https://www.ncbi.nlm.nih.gov/pubmed/23974637) of [death from influenza](https://www.ncbi.nlm.nih.gov/pubmed/27385315). Obesity is correlated with [severe soft tissue infections](https://www.ncbi.nlm.nih.gov/pubmed/28069657), [urinary tract infections](https://www.ncbi.nlm.nih.gov/pubmed/26518067), and [sepsis mortality](https://www.ncbi.nlm.nih.gov/pubmed/29677586).
Only non-influenza pneumonia appears to be less severe in obese patients, a finding known as the [obesity survival paradox](https://www.ncbi.nlm.nih.gov/pubmed/24722122).
So from a MD standpoint it seems highly implausible that obesity would be protective against infectious disease, or that lean muscle mass would confer susceptibility to infectious disease.
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askscience
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> throughout most of human existence, females have NOT been the ones picking mates.
I don't think that's clear. Since pre-historic/pre-agricultural societies represent most of our time on the planet, theories about the overall societal context in which we evolved are quite speculative. There is evidence against female choice, and evidence that supports female choice - but I'm not sure anyone knows enough about those trends to discount female choice as a major force in early societies.
It's also important to note that societal domination of an individual woman does not usually mean that female mate preferences are inert. Female desire is often integrated into matchmaking/arranged marriage practices in formal or informal ways. The fact that a boy is good-looking and lovable etc. will usually raise his value in an arranged marriage market. Furthermore, only a small minority of observed arranged marriage systems do not give the woman veto power over a match. I'd wonder whether there are any societies that developed their matchmaking methods with total disregard for the possibility that woman's rejection of her husband, based on lack of attraction, could screw things up.
I don't buy entirely into the idea that immediate-return hunter gatherers were a bunch of slutty egalitarians. However, we have evidence of practices that obscure paternity, and a lot of practices that give opportunities for sexual promiscuity. We also know that general egalitarianism correlates with more freedom for women - and if these societies heavily tended toward egalitarianism (as suggested by proponents of H-G egalitarianism like Peter Gray and Christopher Boehm), we could imagine that this would dispose them toward greater expression of mate choice.
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askscience
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The relvant span for evolutionary history, the kind that is relevant when discussing genetic reflections of observed behavior as here, is far far longer than any cultural history we currently have clear evidence for. For that span, we search for the effects in biology itself, hence the mention of actual observable sexually selected for traits in humans males/females, (and as opposed to traits selected for direct survival value). And that shows an abundance in females as mentioned above and a relative paucity in males. That alone is overwhelming evidence that at least in humans, in relevant latest evolutionary history, the sexual selection pressure has been disproportionately on females, which an only come about if males are doing most of the picking, and consistently for long periods of time. For instance, disproportionately big human female breasts offer no survival value, they exist so far out of the norm in humans compared to all other mammals, solely because men selected for those.
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askscience
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> For that span, we search for the effects in biology itself, hence the mention of actual observable sexually selected for traits in humans males/females, (and as opposed to traits selected for direct survival value). And that shows an abundance in females as mentioned above and a relative paucity in males. That alone is overwhelming evidence that at least in humans, in relevant latest evolutionary history, the sexual selection pressure has been disproportionately on females, which an only come about if males are doing most of the picking, and consistently for long periods of time. For instance, disproportionately big human female breasts offer no survival value, they exist so far out of the norm in humans compared to all other mammals, solely because men selected for those.
That's contentious because traits that represent male attractiveness and traits that represent increased ability to compete with other males (or thrive in other ways) often overlap. If a woman picks the guy who can win a fistfight, that doesn't mean that she hasn't made a true choice, and also doesn't mean that a man who can fight isn't required to win the affection of women in order to mate. A physical anthropologist is limited in determining whether such a trait is a result of force or choice - that's one reason why we go back to the cultural data, even if it's quite thin.
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askscience
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Climate change will have weird effects on hurricanes that are not well understood. There is significantly more energy in the atmosphere because of it, but hurricanes are caused by a very complex mix of many factors like temperature gradients, wind shear, ocean temperatures and currents, the jet stream, etc. All of these are likely to change in a warmer world, but some of them will have an impending effect to hurricane development while others will worsen them. All said, the threats from global warming are significant and existential, but mega hurricanes aren’t likely to be a big part.
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askscience
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Hurricanes are not becoming more frequent nor are they expected to. At least the last two IPCC reports have stated that hurricane frequency will either remain steady or decrease. But intensity is and is expected to continue increasing in a warming world.
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Tropical cyclones and climate change (Knutson et al, 2010) - [http://shoni2.princeton.edu/ftp/lyo/journals/Knutson-etal-TCClimateChange-A-NatGeoSci2010.pdf](http://shoni2.princeton.edu/ftp/lyo/journals/Knutson-etal-TCClimateChange-A-NatGeoSci2010.pdf)
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"However, future projections based on theory and high-resolution dynamical models consistently indicate that greenhouse warming will cause the globally averaged intensity of tropical cyclones to shift towards stronger storms, with intensity increases of 2–11% by 2100. Existing modelling studies also consistently project decreases in the globally averaged frequency of tropical cyclones, by 6–34%."
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Response of Tropical Cyclone Activity and Structure to Global Warming in a High-Resolution Global Nonhydrostatic Model (Yamada et al, 2017) - [https://journals.ametsoc.org/doi/full/10.1175/JCLI-D-17-0068.1](https://journals.ametsoc.org/doi/full/10.1175/JCLI-D-17-0068.1)
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"The model projected that the global frequency of TCs is reduced by 22.7%, the ratio of intense TCs is increased by 6.6%, and the precipitation rate within 100 km of the TC center increased by 11.8% under warmer climate conditions."
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Dealing with current trends we see the following:
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Increasing destructiveness of tropical cyclones over the past 30 years (Emanuel, 2005) - [https://nature.berkeley.edu/er100/readings/Emanuel\_2005.pdf](https://nature.berkeley.edu/er100/readings/Emanuel_2005.pdf)
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"Here I define an index of the potential destructiveness of hurricanes based on the total dissipation of power, integrated over the lifetime of the cyclone, and show that this index has increased markedly since the mid-1970s. This trend is due to both longer storm lifetimes and greater storm intensities. I find that the record of net hurricane power dissipation is highly correlated with tropical sea surface temperature, reflecting well-documented climate signals, including multi-decadal oscillations in the North Atlantic and North Pacific, and global warming."
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Deconvolution of the Factors Contributing to the Increase in Global Hurricane Intensity (Hoyos et al, 2006) - [http://faculty.jsd.claremont.edu/emorhardt/159/pdfs/2007/Hoyos%20et%20al.%202006.pdf](http://faculty.jsd.claremont.edu/emorhardt/159/pdfs/2007/Hoyos%20et%20al.%202006.pdf)
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"The results show that the trend of increasing numbers of category 4 and 5 hurricanes for the period 1970–2004 is directly linked to the trend in sea-surface temperature; other aspects of the tropical environment, although they influence shorter-term variations in hurricane intensity, do not contribute substantially to the observed global trend."
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The increasing intensity of the strongest tropical cyclones (Elsner et al, 2008) - [http://www.ssec.wisc.edu/\~kossin/articles/nature07234.pdf](http://www.ssec.wisc.edu/~kossin/articles/nature07234.pdf)
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"We find significant upward trends for wind speed quantiles above the 70th percentile, with trends as high as 0.3 ± 0.09 m s-1 yr-1 (s.e.) for the strongest cyclones."
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Trend Analysis with a New Global Record of Tropical Cyclone Intensity (Kossin et al, 2013) - [http://journals.ametsoc.org/doi/full/10.1175/JCLI-D-13-00262.1](http://journals.ametsoc.org/doi/full/10.1175/JCLI-D-13-00262.1)
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" This additional homogenization step is found to measurably reduce LMI trends, but the global trends in the LMI of the strongest storms remain positive, with amplitudes of around +1 m s-1 decade-1 and p value = 0.1. Regional trends, in m s-1 decade-1, vary from -2 (p = 0.03) in the western North Pacific, +1.7 (p = 0.06) in the south Indian Ocean, +2.5 (p = 0.09) in the South Pacific, to +8 (p < 0.001) in the North Atlantic."
&#x200B;
Trade-off between intensity and frequency of global tropical cyclones (Kang et al, 2015) - [http://myweb.fsu.edu/jelsner/PDF/Research/KangElsner2015.pdf](http://myweb.fsu.edu/jelsner/PDF/Research/KangElsner2015.pdf)
&#x200B;
"We calculate an average increase in global tropical cyclone intensity of 1.3 m s-1 over the past 30 years of ocean warming occurring at the expense of 6.1 tropical cyclones worldwide."
&#x200B;
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askscience
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If the Gulf Stream is disrupted, the maritime climates it warms will turn more like Alaska or Newfoundland (this is the scenario that's fictionalised at the start of The Day After Tomorrow). The disruption is from changes to currents in the Atlantic, which alter in salinity because of lots of melting ice entering the sea. So global warming causes ice melt causes local loss of a heating current.
Heaven only knows what that would do to the Atlantic hurricane season..!
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askscience
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The search for dark matter comes from a discrepancy between how much mass we think there is in certain cosmic structures (such as galaxies) based on what we can directly measure and how much mass we think there is based on the motion of objects that we observe.
We can estimate the mass of something like a galaxy by measuring the amount of light it emits (and correcting that for distance) using the knowledge that we have on the structure of stars and how mass and light emission are related.
But we can also look at the gravity exerted by cosmic objects. The heavier something is, the larger its effect on the motion of nearby objects (among other things). So by analyzing the motion of cosmic objects, we can estimate masses as well.
And when we put these two approaches next to each other, they don't match. At all. Estimates based on gravitational effects suggest a mass that is much higher than estimates based on direct observation of emissions.
There are two reasonable explanations for this large discrepancy. Either there is something there that we can't see, but that's rather heavy. Or our theories on how gravity, stars and other cosmic objects work are wrong.
This issue was first raised in the late 19th century. Since then, our knowledge of astrophysics has increased enormously, thanks both to theoretical advancements and to powerful observational tools. But with every advancement, the mass discrepancy remained. And with time, astrophysicists have gathered more and more evidence to support the idea that there indeed is some form of matter that we can't readily detect with our telescopes and other equipment.
So we don't know for certain that dark matter exists. However, by now it is by far the most plausible explanation for all the observations that suggest there is a more matter in the universe than what we can directly observe. And as such, it has become the mainstream consensus that some type of matter probably exists that is hard to detect, but is present in large quantities in and around galaxies.
The fact that we don't know what this matter would consist of makes searching for it rather difficult, which is why dark matter is one of the most important open problems in astro- and particle physics.
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askscience
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While black holes don't emit light, the area directly surrounding a black hole, the so-called "accretion disk", contains very hot and dense gases that emit a large amount of radiation, typically in the x-ray part of the spectrum. This allows for detection of black holes by x-ray observatories.
In addition, black holes are by their very nature compact and localized objects. The observations leading to the missing mass point to a mass distribution of dark matter that is smoothly spread across a galaxy.
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askscience
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The mass of planets is just too low. Planets are *tiny* compared to stars. Even if every star were orbited by fifty planets the size of Jupiter, all those planets together would still have only a tiny fraction of the required mass.
If you imagine the planets being massive enough to make up the difference, they would become so massive that they start undergoing fusion. Those would no longer be planets; they would be stars, and we'd have been able to see them.
Cosmologists have also considered the possibility of "rogue" planets floating around outside solar systems. The problem there is that you'd need zillions of rogue planets to make up the missing mass. If they were that numerous, we would at least occasionally be able to detect some, by seeing them pass between us and a distant star. We have looked for this effect, and have not observed it. That means rogue planets are not nearly common enough to be the explanation.
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askscience
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All of the scientist jokes out there\* are centred on the theme that astrophysicists are used to working with a sample size of one.
In their pre-Kepler defence, the Sun is a super-boring star that's slap bang in the middle of the main sequence, so it's not a terrible single sample. Now that Kepler has done its thang, our Sun is just one example out of thousands, and they too came up orders of magnitude short.
&#x200B;
\*or at least that's what an astrophysicist told me after he heard the Scottish cow joke.
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askscience
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Melted paper is certainly possible.
Burning only happens in the presence of oxygen, so remove oxygen and heat anything high enough and it will melt.
The factor which decides which materials behave which way in the presence of oxygen depends on which of the two phenomena requires the least amount of heating for any given material, as this is the one which will happen before the other has the chance to.
For example, if a material would need to be 1000K to melt, but could burn at 700K when oxygen is present, it would burn before it melts, leaving you with the product of combustion.
However, another material may melt at 700K and require a theoretical temperature of 1000K to burn it. In this case it would melt. The liquid may then burn at some temperature, which may not necessarily be the same temperature as the one theoretically needed to burn it.
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askscience
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What you would most likely see is that the intermolecular forces holding the polymer strands of the paper together would break first, which would cause the paper to melt.
Then with more heat added the chemical bonds of each strand would start breaking down later.
However, it is also entirely possible that for some polymer strands may be configured in such a way that the intermolecular bonds holding each strand together ‘outlast’ the chemical bonds of each individual strand. But this scenario is far less likely as generally the intermolecular bonds are far weaker.
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askscience
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If oxygen is present, the wood will be undergoing combustion and those gasses are carbon dioxide amongst a few others.
If it is in a vacuum, you are melting and then evaporating the wood (you would need ridiculously high temperatures for this) and you would be getting gasses from breaking the intermolecular bonds of the chemicals that makes up wood.
It may well be the case that you ionise the chemicals in the wood before they evaporate, I’m not 100% sure.
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askscience
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As far as I'm aware, we still don't *quite* know.
Compared to humans, we've known for some time that insects are generally more resistant to ionizing radiation, and multiple hypotheses have been proposed to explain this radioresistance.
For a long time it was thought that because actively dividing cells are those most sensitive to radiation, insects would succumb less as, unlike humans with our leagues of constantly dividing cells, insects undergo discontinuous periods of growth (only with every moult). But this whole organism approach to radioresistance was tricky to interpret, as the physiology between us and, say, invertebrates is very different.
At a cellular level however, experiments on cells controlling for proliferative rate have revealed that insect cells are *de facto* more radioresistant than human cells, leading us to believe division rate actually might only have a little to do with it. When you blast human and insect cells with ionising radiation, the DNA within the insect cells itself undergoes much less damage, and what damage is present is more effectively repaired. Likewise, those same insect cells experience lower oxidative stress as a consequence of radiation exposure (radiation triggers the production of rather harmful reactive oxygen species that, amongst other things, trigger cells to commit [apoptotic](https://en.wikipedia.org/wiki/Apoptosis) suicide).
So yup, it appears the suite of repair enzymes insects utilise are simply better at dealing with DNA damage, explaining why insects have greater radioresistance. As for the evolutionary reason why they're more efficient, we're still not quite sure.
___
^**Sources:**
[^(Cheng, I.C, Lee, H.J. & Wang, T.C. (2009)^) ^(Multiple factors conferring high radioresistance in insect Sf9 cells. *Mutagenesis* 24 (3)^), ^259-369](https://academic.oup.com/mutage/article/24/3/259/1074431)
[^(Bianchi, N.O., Lopez-Larraza, D.M. & Dellarco, V.L. (1991)^) ^(DNA damage and repair induced by bleomycin in mammalian and insect cells. *Environ Mol Mutagen*. 17, 63-68)](https://onlinelibrary.wiley.com/doi/abs/10.1002/em.2850170110) ^((research gate) [^here](https://www.researchgate.net/publication/227933716_DNA_damage_and_repair_induced_by_bleomycin_in_mammalian_and_insect_cells)^)
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askscience
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Insect DNA is much simpler than humans, plus simpler body, and organs means they can take more damage without dying.
Look at experiments were a beheaded cockroach survived for days, and was even able to copulate, and reproduce.
You have to kill a majority if cells in most insects before they die, whereas in a human death of a small amount of cells causes a deadly malfunction.
The most sensitive parts of the human body are highly specialized internal organs, insects simply do not have. (Liver, spleen, bone marrow,....)
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askscience
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Hmm, it's tempting to think the presence of a chitinous exoskeleton might have some influence too. Alas, I've failed to find any evidence to support the claim. If anything, according to [this](https://www-pub.iaea.org/MTCD/Publications/PDF/P1731_web.pdf) sourced from [here](https://inis.iaea.org/search/searchsinglerecord.aspx?recordsFor=SingleRecord&RN=26023735), marine invertebrate chitin shells readily degrade under exposure to ionising radiation; though a contradictory claim by [this material science paper](https://link.springer.com/content/pdf/10.1007%2FBF02515335.pdf) seems to suggest the material itself is quite resistant (in either case, structural resistance doesn't mean it blocks its passage, or anything). I'm a bit out of my depth on this, so haven't really a clue, sorry!
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askscience
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I remember a genetics tutor I had talking about this. Someone had asked him some speculative question about organisms in higher radiation environments and whether they'd evolve faster and his answer was along the lines of ".... probably not, organisms seem to be able to dial up or down their DNA repair mechanisms to an almost arbitrary extent, there seems to be some happy-medium mutation rate that organisms tend towards"
Even humans living in areas with very high natural background radiation appear to respond differently to radiation exposure:
https://www.ncbi.nlm.nih.gov/pubmed/11769138
>People in some areas of Ramsar, a city in northern Iran, receive an annual radiation absorbed dose from background radiation that is up to 260 mSv y(-1), substantially higher than the 20 mSv y(-1) that is permitted for radiation workers. Inhabitants of Ramsar have lived for many generations in these high background areas. Cytogenetic studies show no significant differences between people in the high background compared to people in normal background areas. An in vitro challenge dose of 1.5 Gy of gamma rays was administered to the lymphocytes, which showed significantly reduced frequency for chromosome aberrations of people living in high background compared to those in normal background areas in and near Ramsar. **Specifically, inhabitants of high background radiation areas had about 56% the average number of induced chromosomal abnormalities of normal background radiation area inhabitants following this exposure.**
There are organisms that were found living inside a running nuclear reactor, extremely radioresistant and capable of using some kind of melanin-like compound to harvest energy from the radiation.
https://en.wikipedia.org/wiki/Cryptococcus_neoformans
https://en.wikipedia.org/wiki/Thermococcus_gammatolerans
>While a dose of 5 Gy is sufficient to kill a human, and a dose of 60 Gy is able to kill all cells in a colony of E. coli, Thermococcus gammatolerans can withstand doses of up to 30,000 Gy, and an instantaneous dose of up to 5,000 Gy with no loss of viability.
(on a related note there's at least one [hyperthermophile](https://en.wikipedia.org/wiki/Hyperthermophile) bacteria that can not only survive autoclave themperatures but can reproduce while the autoclave is still running. )
>able to double its population during 24 hours in an autoclave at 121 °C
Living things are awesome.
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askscience
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Oxidative stress usually refers to [Reactive Oxygen Species (ROS)](https://en.wikipedia.org/wiki/Reactive_oxygen_species). Generally, peroxides, superoxides and oxygen radicals, rather than O2.
Having more O2 in tissues may indeed have an effect on ROS generation in irradiated tissues, as you suggest. However, there are also many biochemical mechanisms for neutralizing ROS. These mechanisms can be quite different among different species. Plants are both the most susceptible (due to photosystems harvesting light radiation, as food) and the most resilient (protective biochemical adaptation). Insects, plants and mammals would have some common and some unique ROS detox biochemical pathways.
Another difference may be diet. Plants produce antioxidant molecules (eg Vitamins C and E). Differences in animal resistance to radiation may relate to food sources and quantities.
&#x200B;
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askscience
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Some of my research is in radiation dosimetry. Here is some reasoning behind effects which arise solely from the size of the organism.
1. A mean free path (mfp) is the average distance that a particle travels through some medium before interacting with an atom or molecule in that medium. If radiation passes through an organism or any medium without interacting, there is exactly no effect on that organism or medium.
2. Ionizing radiation is simply a particle with enough energy to ionize an atom or molecule. (It also must either be charged or create charged particle upon interacting, but I'm only saying this to be thorough.)
3. Higher energy generally means a longer mfp.
4. If you compare two organisms of different sizes, the smaller one is simply a smaller medium which has shorter paths for radiation to traverse.
5. Most of the ionizing radiation we care about has a mfp on the order of centimeters. The probability of some ionizing radiation interacting in the smaller organism is just lower.
Of course, this doesn't consider different biologies of organisms. That also can be a factor. To compare an organism's susceptibility to radiation damage, you have to look at its size, the type of radiation it's exposed to, it's biology, and it's stage in it's life cycle.
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askscience
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> As for the evolutionary reason why they're more efficient, we're still not quite sure.
Could it simply be quantity of cells and trying to balance risk of cancer vs risk of radiation?
> those same insect cells experience lower oxidative stress as a consequence of radiation exposure
When insects arrived in the Carboniferous period in which Oxygen levels rose [75% higher than today](http://forces.si.edu/atmosphere/02_02_06.html). Could they have evolved to better repair from the damages of oxidation and never lost the ability?
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askscience
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It's very interesting how there is a clear relationship between body mass and radiosensitivity among multicellular animals. To the best of my knowledge, no one has a proven explanation for why this is. But as a radiation oncologist, my scientific wild-ass guess is that larger animals trade radiosensitivity for cancer resistance.
Larger animals are paradoxically less prone to cancer than smaller animals. It's such a bizarre yet consistent phenomenon that it has a name, [Peto's Paradox](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3060950/).
An insect is a small-bodied and short-lived animal, which means that it is relatively insensitive to cancer risk. An insect's cells can express very high levels of DNA repair machinery. Even if those DNA repair mechanisms were highly error-prone, the insect is very unlikely to die of cancer before it naturally dies of old age. On the other hand, an insect with low levels of DNA repair would be much less likely to survive a caustic chemical or radiological (inculding sunlight) environment. So evolution favors the higher level of DNA repair.
A human is a large-bodied and long-lived animal, which means that we have to be relatively resistant to cancer or else we would never live as long as we do. A human cell with severe DNA damage is better off dying through apoptosis or immunological cell killing, so that it does not create a risk for malignancy.
If a human expressed extremely high levels of error-prone DNA repair, he/she would become more cancer-prone and his/her fitness would decrease. On the other hand, humans with low levels of DNA repair would minimize their cancer risk, in exchange for being less capable of tolerating chemical or radiological/solar injury. So evolution has given humans a low (but functional) level of DNA repair.
One of the things we know about DNA double-strand-break repair is that it can always make mistakes. Despite the classical textbook description of "error-prone NHEJ repair" and "high-fidelity HR repair", [both pathways have nonzero error rate](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4052342/) and can cause permanent genomic alteration.
In addition, any cell with a radiation-induced lethal double-strand break (DSB) would likely have a much larger number of non-DSB DNA lesions. [Clustered base damage](https://www.sciencedirect.com/science/article/pii/S0936655513002471) is an active subject of research in radiation therapy and space medicine.
Again, repairing a clustered-damage site could result in permanent genetic alteration, which could lead to cancer. A long-lived mammal may not want their cells to repair clustered damage as efficiently as possible. Our cells may prefer to sacrifice themselves in order to promote the lifespan of the individual.
-none of this is backed up by hard evidence, it's a hypothesis, but it makes sense to me-
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askscience
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Considering that the most common form of DNA-damaging radiation on Earth is ultraviolet light, and UV has very little penetration into biological tissue, it's quite plausible that a thin carapace would greatly mitigate DNA damage from the Sun.
That said, most of the strongly-ionizing radiation comes from cosmic sources or inhaled/ingested sources. Cosmic rays are very deeply penetrating and no realistic amount of biological tissue is going to block them. Inhaled and ingested sources deliver a dose from within, so skin/carapace thickness is irrelevant.
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askscience
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Could the radioresistance of insect cells have evolved in response to an atmosphere that absorbed less radiation? That is to say, the common ancestors of insects that are not the common ancestors of larger, more radiosensitive, creatures developed the trait due to different environments... My immediate thought is water. That insects started crawling on land when the sun was more of a deadly laser than when the fishies started flailing about on the hard-bit-that-leave-home.
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askscience
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> Look at experiments were a beheaded cockroach survived for days, and was even able to copulate, and reproduce.
This is because in insects the brain in the head does not control all of the nervous system, but only a handful of functions. They have various ganglia throughout their bodies that control most of their functions, including movement, sexual function, etc. I don't really think this has any affect on resistance to ionizing radiation.
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askscience
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In addition to the path length, it's also something to consider that an organism with more cells exposed to radiation simply has more chances of harmful radiation damage.
From radiation that gives an incidence of 1 mutation event per 1000 cells; an organism with 1031 cells (c. elegans) should get around 1 mutation, and an organism with 37 trillion cells (an estimate of humans) should expect 37 billion mutations. Obviously not all mutations are harmful or lethal, but by simple numbers, 37 billion chances at a deleterious mutation for the organism as a whole is a lot worse than one. And that's without adding in path length or looking at repair biology.
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askscience
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Radiation can be measured in a lot of different ways, especially when measuring its effects on things. Radioactive materials both emit some level of radiation as well as decay at some rate, living organisms have a tolerance for both a momentary dose of radiation as well as accumulating radiation over time, and there's different wavelengths to work with too.
For different reasons, but to a similar effect, electricity has a ton of units too. Because of all the ways it can affect other things and be affected, and how different properties of it will be responsible for different effects, it's impractical to measure it by just one or two units.
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askscience
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Absorption is the fundamental principle of radiation shielding. If ionizing radiation is going to pass through you, there are two possibilities. It is absorbed somewhere along the way, or it carries on through. If it just goes through you are fine. So you only have to worry about it being absorbed.
If it is going to be absorbed then you need to make sure it doesn't interact with anything important. Since all that we can control is the probability of something being absorbed, not what it is absorbed by. As such we maximize the chance that it is absorbed by something we don't care about. Say a big block of lead.
That is why radiation shielding is almost invariably a big dense block of metal since that is the cheapest and easiest way to achieve that effect. Though huge bodies of water or oil are sometimes also used.
As for making the chitin radioactive. It might, but if it did it would be only very slightly radioactive.
Chain reactions like that we see in nuclear weapons only happen because the output of one decay is enough to push other nuclei over the edge which only really happens with large nuclei like Uranium and up.
Chitin is made of carbon, nitrogen, oxygen, and hydrogen. While all of these have radioactive forms, we see in Carbon, for example, the isotope carbon-14 is only very slightly radioactive. It decays so slowly that we can use it to work out when things died from millions of years ago. And even then, these small atoms simply don't have enough energy (unless you put your poor insect into a particle accelerator) to put out anything ionizing, it's no threat.
That said, I honestly don't know how effective a radiation shield it would be. That depends on its density, and since chitin is a messy bio-polymer, and only really exists in thin layers, I can't really say.
I'd guess that it has some effect, but the effect size would be so small that useful results would be very very difficult to get. Other factors would be more important. Has anyone looked at a correlation for genomic length and radiation resistence?
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askscience
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The basic difference is between physics and biology.
And there are different standards, like between Centigrade and Fahrenheit for temperature.
Physical units:
The original unit was the roentgen, which measured ionization in air of x-rays = 2.58×10e−4 Coulombs/kg. It's now obsolete.
1 rad is physical, defined as 100 ergs deposited per gram in CGS units. In animal tissue, it's about 1.04 Roentgens
The SI (International System, more common in Europe)) preferred to measure the same thing as Joules/Kg, and called it the Gray, which is equivalent to 100 rads.
But more relevant for biology:
Different kinds and energies of radiation (eg alpha, beta, and gamma rays) can have very different effects, mainly related to density of ionization.
So they defined the rem, (roentgen equivalent man) as the dose of any kind of radiation that will give about the same biological effect as 1 rad of x or gamma rays. Each kind of radiation has a conversion factor from rads to rem called the RBE (Relative Biological Effectiveness)
And the SI unit for that is called the Sievert, which = 100 rem.
Other units are used just to describe how active radioactive isotopes are:
the curie (Ci) is 3.7×10e10 decays/second, but the SI system defined the becquerel (Bq) as 1 decay/second , so they're usually talking about Giga Bequrels (GBq)
Eventually they ran out of dead physicists to name things after, so they quit.
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askscience
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> Having more O2 in tissues may indeed have an effect on ROS generation in irradiated tissues, as you suggest.
Exactly, which is one reason why (as far as I remember) oxygenation makes a huge difference to radioresistance in tumors.
> However, there are also many biochemical mechanisms for neutralizing ROS.
Yeah, and thanks for the interesting overview. I still wonder which factor is most important (and if there is any difference between vertebrates and invertebrates in terms of typical cell oxygenation.
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askscience
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It would be possible contingent upon ionizing radiation being a major factor in natural selection - if lots of insects are dying from radiation, preventing them from reproducing. Only the resistant ones would survive and reproduce.
I personally think if they are more resistant, natural selection is selecting on something else, which just happens to confer resistance to ionizing radiation too - difference in cellular biology that happens to benefit them.
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askscience
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I'm not the best suited to give an in-depth explanation, but I would note that angiosperms as a whole are relatively recent in the evolutionary timeline of plants, which have been around for about 480 million years.
The first flowering plants diverged from gymnosperms about 200-250 mya, and angiosperms became widespread about 120 mya (so about the last quarter of the entire existence of the plant kingdom).
Poaceae (the family that contains grasses) was originally thought to be around 55 million years old, but older fossil evidence keeps turning up. Plant structures associated with grasses have been found in fossilized dinosuar feces dating back to 66 mya, and revised dating of the rice tribe and fossil evidence of mammals with apparent grass-feeding adaptations have pushed the origins of Poaceae back to around 100-120 mya, about the same time that flowering plants became widespread.
As far as the make-up and distribution of plant communities prior to the emergence of grasses/grasslands/angiosperms in general I really don't know. Nor do I know much about erosion and soil formation at the time plants first began to colonize land.
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askscience
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> Poaceae (the family that contains grasses) was originally thought to be around 55 million years old, but older fossil evidence keeps turning up. Plant structures associated with grasses have been found in fossilized dinosuar feces dating back to 66 mya, and revised dating of the rice tribe and fossil evidence of mammals with apparent grass-feeding adaptations have pushed the origins of Poaceae back to around 100-120 mya, about the same time that flowering plants became widespread.
This is correct, but I feel needs to be added to: there is an important difference between the evolution of grass and the emergence of the grassland. It took grass a while before it was truly defining it's own biome. Last I heard was around 25 mya, but that may have been since updated.
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askscience
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That’s all correct (with the caveat that others have mentioned of *grasslands* being a more recent phenomenon and a different thing than the emergence of grasses themselves).
Ground-covers in the Cretaceous and earlier appear to have largely been ferns, mosses (true mosses and club-mosses), and biocrusts (mixtures of lichens, algae, liverworts, and mosses). Given the relatively early dates of flowering plants there were undoubtedly some forbs mixed in as well, but not in significantly highe enough densities to leave a strong fossil record. It would not be surprising if there were some small, ground-cover adapts confiers or conifer relatives, but I’ve never read of those being found. In more damp areas horsetails would be common as well.
Ferns, once established, can be extremely tenacious (as are horsetails) due to their rhizomatous growth (a network of tough underground stems from which new plants can grow even if they are broken).
Picture [a landscape like this one](https://www.flickr.com/photos/7leagueboots/4918049904/in/album-72157624784344336/), but with the trees replaced with conifers instead, or the sword fern and redwood/Douglas fir forests of the Pacific Northwest (at least for wet areas).
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askscience
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I suspect it depends a lot on the type of fern, but where I took that photo (Appalachian Trail in Shenandoah NP, Virginia) and elsewhere along the East Coast the lack of apex predators and the resulting [overpopulation of white-tailed deer seems to a major driving force](https://extension.psu.edu/controlling-understory-fern-competition-for-regeneration-success).
Many types of fern (and things like hobble-bush) are not preferred forage for the deer. They selectively eat what they like, leaving the plants they don't, which gives those plants, ferns especially, enjoy a competitive advantage as a result. Hay-scented fern is one of the ones that's often considered a "problem" fern in that part of the US.
On the West Coast it's a bit different, the old-growth tall forests are dark which limits what can grow in the understory. Certain ferns tolerate the dark well and grow so densely that they effectively drown out other plants. Not all others, obviously, but enough so that they dominate.
Situations like this are why the occasional blow-down is so important in old, primary growth forests. Blow-downs open up the forest to light and promote the growth of important species that have been sort of "waiting in the wings" for the opportunity to grow.
[Allelopathy, of a more chemical nature, also plays a part, particularly in the case of bracken ferns](https://www.researchgate.net/publication/226278266_The_allelopathic_mechanisms_of_dominance_in_bracken_Pteridium_aquilinum_in_Southern_California) and studies have been done on a wide variety of other ferns, indicating that this is a trait that is widespread. Of course, it's a mix of factors that leads to suppression of other plants, in the linked paper one of the findings was that small animals sheltering in bracken fern stands foraged on seedlings and suppressed the growth of certain plants as a result.
Like a lot of things, the full answer is complex.
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askscience
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So if I have two stars, one light year apart, and this is more of a though experiment than an actual situation, and they wink into existence at the same time, It would take one year for those stars to have any type of gravitational force on each other?
And to expand, from the perspective of each of those stars, would the other one not even "exist" for the first year since their light would need a year to travel to the other one?
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askscience
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I suppose that's a variable I did not take into consideration. Perhaps I overestimated the influence the Earth has on the moon simply because it's so close to us. Makes me think of all the other variables like what if the earth vanished when the moon was in orbit away from the sun as opposed to moving toward it. Altenratively if it made a full stop before being affected by gravity again.
Thank you for your answer!
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askscience
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The earth orbits the sun with a speed of ~30km/s.
The moon orbits the earth at ~1km/s.
So if the moon is going "forwards" when earth vanishes, it has an orbital velocity of 31km/s around the sun, if it goes "backwards" in that moment, it's 29km/s. So it would only get to a slightly different orbit depending on the time earth vanishes. Movement perpendicular to its current direction (towards the sun or away) will only make the orbit more elliptical, but the average orbiting distance stays the same cause the speed stays the same.
To fall into the sun, a body needs to get rid of all the speed it's currently orbiting with.
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askscience
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Earth's orbital speed round the Sun is 30 km/s . The Moon's orbital speed round the Earth is 1 km/s. So if the Earth vanished, the Moon's orbital speed round the Sun would be between 29 and 31 km/s, not a huge difference. (I think that wouldn't be enough to make the Moon cross the orbits of Venus or Mars but I'd need to check.)
For other moons the effect could be more dramatic. Io and Europa orbit Jupiter faster than Jupiter orbits the Sun, so if Jupiter vanished then those moons could be put on an escape trajectory, or a retrograde orbit round the Sun, or if the position is just right they could impact the Sun after Jupiter's disappearance.
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askscience
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Suppose the Moon, or the Earth, or any object significantly less massive than the Sun winked into existence 1 AU from the Sun, with a heliocentric velocity of zero.
Ignoring the minor effects of the other planets, that object would immediately begin accelerating toward the Sun at puny 5.93 mm/s^2. As the object approaches the Sun, its acceleration and speed increase further, decreasing its distance even faster, in a positive feedback loop.
Q. So how much time will elapse before our magic object impacts the Sun's photosphere ?
A. TBD
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askscience
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>If the Earth vanished, the moon will simply continue orbiting the sun with minor changes to its current trajectory.
To put numbers on "minor changes": the Moon would enter an elliptical orbit whose distance from the Sun was never more than 14% different from if the Earth's orbit now. Whether it would go closer to the Sun or farther depends on where the Moon was in its orbit when the Earth disappeared, but it wouldn't get anywhere near Mars or Venus.
[https://en.wikipedia.org/wiki/Vis-viva\_equation](https://en.wikipedia.org/wiki/Vis-viva_equation)
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askscience
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The mass of the earth and/or moon is nothing compared to the mass of the sun so the mutual attraction stays roughly the same.
The escape velocity from the sun does not depend on the mass of the object orbiting it, assuming the object has no significant mass compared to the sun. Escape velocity from the sun from earths position is about 40 km/s and earth/moon orbit is 30 km/s so you need at least 10 km/s extra in the right direction.
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askscience
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A shell or ball is what you'd expect if the particles don't collide with each other. This is why you can get elliptical galaxies - stars almost never collide and don't even have close encounters very often, so once you get a ball of stars, the stars will just keep on buzzing around in a ball for a very long time. This is also supposed to be the case for dark matter. The dark matter particles don't really collide with each other, so they just stay in a big puffy "halo" around the galaxy.
However, the dust and rocks and moonlets in a planetary ring *can* collide with each other. So if you some particles in a "polar" orbit, going up over the north pole and back around the south pole, and other particles in an "equatorial orbit", going in circles around the equator, then these particles will smash into each other. Unless all the particles are orbiting in the same plane, their orbits will cross and they'll collide. These collisions transfer momentum between the particles, and also get rid of kinetic energy. Eventually, through enough collisions, everything will settle down until you get a disc or a ring. Then all the particles can have nice circular orbits without bumping into each other. (Another way to think of it is this: you can get rid of energy, but you can't get rid of momentum. A ring or disc is the lowest energy system you can get while still conserving angular momentum).
This is true for more than just planetary rings. Gas and plasma particles in space will bump into each other too. So when you get a lot of gas coming together to form a galaxy - or, on a smaller scale, a chunk of gas coming together to form a star - it will also collapse into a disc. For a galactic gas disc, this will collapse to form stars, so you get a disc of stars. For a stellar gas disc, this will collapse to form planets, so you get all the planets within the same plane. It's not that the stars or planets need to be in a disc - neither really is good at collisions - it's that the gas they formed from was in a disc.
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askscience
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>So if you some particles in a "polar" orbit, going up over the north pole and back around the south pole, and other particles in an "equatorial orbit", going in circles around the equator, then these particles will smash into each other.
Does the spin of the planet also play a role? Do any planets settle with just north-south "polar" rings, or some other angle, or does the equator always win?
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askscience
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Angular momentum without dissipation just gives you ellipsoids - it doesn't explain discs. You need a way to get rid of the kinetic energy, and that means your particles have to collide with each other. If the ring particles had a small enough cross section and a low enough density that the collision rate was extremely low, then they wouldn't be in so thin a disc, even with the same angular momentum.
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askscience
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Accidentally deleted my last post.
I asked: “Is this like, a really complicated way of explaining angular momentum? Because angular momentum is actually the reason for discs forming and planets orbiting in the orientations that they do.”
Thanks for the response. In the case of planets that we know of, are there any instances where there are clouds of dust surrounding a planet that are not moving toward disc-shapedness? I feel like angular momentum is more important than collisions. Collisions are going to happen, yes, if the density of the cloud is great enough and the particles can collide, but they wouldn’t even be hanging out in the same place if not for gravity/angular momentum.
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askscience
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We don't see this around planets, but that's because the matter is collisional. But we do see blobs of stars. Elliptical galaxies do have angular momentum - they're often ellipsoidal - but because they're not collisional they don't collapse down into a disc.
Basically, angular momentum stretches things out equatorially, but collisional dissipation flattens things vertically. If you don't have angular momentum, dissipation causes everything to collapse into a point. If you don't have dissipation, then you have a big puffy ellipsoid. So you really do need both to get a thin disc or ring.
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askscience
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The debris that formed the planet basically never have _perfectly_ equal angular momentum in all directions (a total angular momentum of zero). As the particles form the planet and ring, the "left over" angular momentum is what determines the axis of rotation. It's not that a certain axis is favored not to cancel out, it's that a certain axis tends to have a bit of surplus after all the cancellations happen.
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askscience
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Much of its mass, yes, but perhaps not most.
I'm guessing that physics models would permit an axial-spin-changing collision that could have possibly been a glancing blow.
In this case, the impactor may have shattered and mostly continued flying on, along with a good chunk of Uranus.
Sure would have been something to see from a half-million miles away or so (and with all sorts of filtering and radiation shielding up. Don't need no Terminator 2 playground scenes, nosirree).
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askscience
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This is fascinating and seems obvious now that I've read it. I feel a little silly for not knowing this previously.
I get that the ring exists because it's stable (stuff not bumping into other stuff). Why does it settle into such a narrow band? It seems like would have a wider band of stuff all going parallel and in the same direction? Maybe because any debris not parallel by even a small amount will eventually disappear due to collisions?
And based on this, would we expect the width of rings to get narrower over time?
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askscience
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Because it's not the whole story.
Very simply put, It's because when a system forms, it starts by matter spiraling inwards. An accreation disk is flat, not round.
Eventually you end up with a body (in this case Saturn) that is spinning. Some matter stayed in orbit and didnt spiral inwards, these condensed in to moons (not counting captured ones).
Some of the matter that stayed in orbit was however so close, that the gravitational pull stopped it from condensing (they were below the roche limit) and you wind up with rings. These rings *do* pull on eachother, so they will eventually be in the same plane.
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askscience
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Imagine the whole debris cloud spinning around a common axis. Everything is (on average) drawn towards the Center of the cloud.
When everything is spinning, there is a virtual force acting away from the axis in a perpendicular direction. That means that each particle exactly on the ring plane has a chance of both the virtual force and gravity cancelling each other out (or almost doing so), while every particle outside that plane experiences a net force "south" or "north", towards that plane, which has no chance of being cancelled out by anything else. Eventually, everything that is not in the ring either collects into the central planetary mass, drifts away into space, or joins the ring in some way.
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askscience
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This is not necessarily true. There is evidence to suggest that Saturn's rings are quite young. In fact, a captured asteroid could result in an orbit that brings it close to the Roche limit long after the formation of the planet, thus producing rings that are not related to the rotation of the planet. However, there are tidal effects with the rings that can slowly shift their axis to align with the rotation axis of the planet.
The key thing here is Uranus. Uranus's high axial tilt suggests that some kind of large collision resulted in an unusual rotational axis, potentially after the formation of the planet. However, the rings of Uranus are equatorial, as are the orbits of most of the moons (approximately). IF Uranus's axial tilt occurred after formation of the rings, then there needs to be some mechanism by which the rings rotated with the planet.
More information is needed. An interesting discussion on this topic is here: https://astronomy.stackexchange.com/questions/8112/how-long-do-planetary-rings-last
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askscience
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It's not "just" a ball of gas. Uranus gets thicker and thicker as you go deeper into it and you'll hit a "mantle" of ice that's the vast majority of its overall weight. There's also an iron core.
A planetoid would cause some heating and major wind if it just hit the upper atmosphere layers, but if it slaps into that mantle really hard, it'll do pretty major things to the planet.
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askscience
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The comet Shoemaker-Levy 9 didn't go through Jupiter... It most definitely impacted. [https://en.wikipedia.org/wiki/Comet\_Shoemaker%E2%80%93Levy\_9](https://en.wikipedia.org/wiki/Comet_Shoemaker%E2%80%93Levy_9)
At enough pressure, and enough speed of the impactor even hydrogen gas acts like a solid.
And even the Earth's own very thin (relative to a gas giant) atmosphere is enough to make a large-ish body stop before getting too far down, as we saw with the Chelyabinsk meteor, which exploded 18 miles above the ground. [https://en.wikipedia.org/wiki/Chelyabinsk\_meteor](https://en.wikipedia.org/wiki/Chelyabinsk_meteor)
Each of these objects hit enough "stuff" to be stopped and release a huge amount of kinetic energy... I consider that an impact, despite not touching anything that I'd consider solid.
(Though, to be even more pedantic than I have already been, I used the word 'collision' rather than 'impact'... Whichever verb we use, though, the result is the same: Uranus' atmosphere is more than thick enough to stop anything that it touches, and with explosive results.)
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askscience
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Another more condensed way to say it (perhaps less intuitive though) is:
The debris cloud stars out shell-like. Through many collisions the particles exchange momentum back and forth. When two particles collide, they preferentially cancel the parts of each other’s momentum vectors that are directly opposite of each other. The cancelled momentum never comes back into the system. All the momentum that remains in the system after many collisions is the angular momentum that lines up with the overall system aggregate. Particles with aligned momentum rarely collide because they are orbiting in exactly the same direction.
(Orbits will all circularize because of a similar mechanic, I believe. Orbits that cross other orbits due to lateral (radial) motion will bleed out of the system over time until only circular orbits are left.)
A disk-shaped cloud is the resultant shape where the particles all have aligned angular momentum.
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askscience
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well rings can either be from the early stages of planetary formation or the rings could be the result of moons colliding or breaking up. In the first case if the ring is formed during planetary formation it is likely that the angular momentum of the ring and the planet is aligned, so the ring will coalesce around the equator.
In the latter case the ring will have the same angular momentum as the moon. Moons tend to orbit in the equatorial plane so the rings also tend to coalesce in the equatorial plane. But if the moon is not orbiting the equatorial plane neither will the ring.
However I believe that tidal forces may force the rings into an equatorial orbit. But as far as I know it is also unclear how long rings can last. Saturns rings for example a thought to be quite old, but some researchers believe that rings cannot last billions of years. So it is still an open question to some degree.
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askscience
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Friction isn't the only force acting on two colliding objects in space. At high mass and low distance, gravity will also help to attract large masses. You are correct in saying that the collision will spread out the masses of both bodies. However, you have to look at the velocity of the colliding object relative to the planet's frame of motion. After the collision occurs, any debris traveling faster than the escape velocity of the new center of mass will continue away from the planet. The rest (and probably most) of the mass, will either compress together to form a new planet, or continue to orbit the new planet as a moon or a ring.
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askscience
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Nope. Most planet's and moon's gravity is strong enough to keep all its dust, rocks, ice, etc on the surface. Most large rings are caused by moons (like most of Saturn's) or planets (the Sun's asteroid belts) breaking up. There are some rings that form from stuff knocked off or ejected from moons. Usually this second type of ring is formed from volcanos/geysers (like [Saturn's E ring](https://en.wikipedia.org/wiki/Enceladus#Source_of_the_E_ring)) or meteor impacts (like [Chariklo](https://en.wikipedia.org/wiki/10199_Chariklo)) rather than the centrifugal like your spinning ball analogy.
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askscience
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That's because Saturn's rings are mostly formed by bodies that have ventured into the Roche Limit of the planet where the gravitational force from Saturn exceeds the the gravitational force that's holding the body of the smaller object together. Hence breaking said object into smaller pieces.
There's only a fixed range of distance from the planet where this can occur. Thus all of the potential orbital rings would eventually collide with each other.
And as for the Roche Divisions, it could have been possibly been made by gravitational forces from Saturn's moons. The different densities of the materials could have formed layers as a result.
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askscience
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> IF Uranus's axial tilt occurred after formation of the rings, then there needs to be some mechanism by which the rings rotated with the planet.
Let's suppose that Uranus had rings prior to impact when it still had a "normal" axial tilt/rotation direction.
I would imagine a smaller planet impacting Uranus hard enough to knock it sideways would produce a TON of debris, which would be going every which way in orbit. All this debris would collide with the existing ring, and eventually the whole mess would coalesce into a *new* ring, the one we see today.
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askscience
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Please correct me if i misunderstood your post, but that isnt how the discs are formed. Planetary disks are formed due to immense gravitational pull on an orbiting body, such that the gravity felt by the orbiting object at opposite poles and the equator are are different, and over time the orbiting object gets stretched out over the length of the orbit. It has nothing to do with planetary bodies coliding together.
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askscience
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>This is true for more than just planetary rings. Gas and plasma particles in space will bump into each other too. So when you get a lot of gas coming together to form a galaxy - or, on a smaller scale, a chunk of gas coming together to form a star - it will also collapse into a disc. For a galactic gas disc, this will collapse to form stars, so you get a disc of stars. For a stellar gas disc, this will collapse to form planets, so you get all the planets within the same plane. It's not that the stars or planets need to be in a disc - neither really is good at collisions - it's that the gas they formed from was in a disc.
could it follow that the universe is also disc shaped?
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askscience
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As others have said, yes. The Solar System formed from a cloud of gas. One day, some part of that gas became so dense that its gravity caused more gas to fall into it. This was a chain reaction, making more and more gas fall into the dense area. This dense area became the sun.
But some parts of the cloud didn't fall into the proto-sun, and instead began to orbit it, in the same direction that the proto-sun rotated. After many, many years, the gas cloud was compressed into a disk around the proto-sun. This is called the proto-planetary disk. All of the objects in the Solar System - the planets, asteroids, and comets - were derived from this disk. They began similarly to the sun, as dense areas in the gas that attracted more and more gas. But they couldn't get as big as the sun, since the majority of the material had been eaten by it.
This is why the sun, planets, and most asteroids rotate in the same direction. The disk spun in the same direction as the proto-sun, and most of the objects from the disk inherited their spin and orbital direction from it.
In fact, most of those objects still orbit the sun on a single plane - the ecliptic. The ecliptic was defined by the direction the proto-planetary disk spun 4 billion years ago.
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askscience
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This remains the prevalent theory, but at the last Uranus meeting I attended, there were several other very 'interesting' ideas, including that there were two moons, one of which was captured and one which escaped (explaining the lack of a large moon at Uranus), and more than one large collision (the theory argued that one impact would only have tilted the planet so far over, so you need more of them). As ever, Uranus drives controversy!
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askscience
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To add to this, when an object is traveling slowly through the atmosphere the air has plenty of time to get out of the way. Speed that object up enough and the air has more trouble getting out of the way of a moving object and compresses. Once this pressure builds up enough it can very much be like running into a solid. Much like the difference between running your hand under running tap water vs running your hand under a pressure washer.
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askscience
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That impact is both improbable and unlikely, and if you have ever played with a top, the impact kinetic energy has to go somewhere, so Uranus would oscillate wildly on a constantly changing rotation axis, also it would have absolutely no effect on the orbiting ring, which would then no longer be in the same rotational axis as Uranus itself, if, as you state the 'accepted theory', Uranus was collided with. That's the Tower of Babylon which is modern Science. Anything they can't explain, they come up with theories that don't match observed phenomenon, which is supposed to be the basis of all rational knowledge, then those 'Oh look, a squirrel' theories become the 'Given Wisdom' issued from the Holy Ivory Tower Pulpit.
A more accurate theory is that an extra-solar system agglomeration of rocks and ice flew too close to Uranus on that ecliptic, then gravitational forces ripped it apart, then captured the fragments in orbit as they dissipated kinetic energy in collisions, with the remainder fragments ripping back off into the original extra-solar system orbit where it came from. The rings are a cosmic 'skid mark' if you will.
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askscience
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That doesn't fully explain it though. With your hand moving through the air, the air just gets pushed out of the way. With the speed of an impactor on a gas giant, it is going so fast that the air can not get out of the way fast enough and so it compresses in front of the object. This compression is actually what causes the vast majority of the heat when a spacecraft reenters the atmosphere.
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askscience
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The slowest that something could hit a planet is from orbit around that planet... which is still VERY fast.
The closest that a moon can orbit is the Roche limit: "The distance in which a celestial body, held together by its own gravity, will disintegrate due to tidal forces exceeding its gravitational self attraction" (Wikipedia).
For Saturn, that's 60,267km. (Depending on the moon itself, of course. A dense moon will survive closer than a loosely packed one.)
The orbital period for such a body would be 4.19 hours. That means that the slowest a moon can orbit Saturn is about 14,376km/h, or 3.99km/s. This is in contrast to the speed that most objects strike Saturn, going at least at its escape velocity of 35.5km/s.
Once a moon gets closer than its Roche limit, it breaks up, with about half the mass raining down on the planet, and the other half being boosted to a much higher orbit. This happens to be one of the older and most widely taught ideas about how Saturn's rings were formed. (And we get the term Roche limit specifically from Edouard Roche proposing this idea.)
As for how it would look... Probably not as dramatic as the Shoemaker-Levy 9 comet, but would last much longer in duration. When objects hit the atmosphere, the compression of gasses in front of them will heat everything up until it either explodes or slows down to its terminal velocity and drops below the cloud layers, never to see the light of the sun again.
Edit to add:
Note that the 4km/s speed is the speed to stay in orbit at the Roche limit. Once the moon starts breaking up, parts of the moon will go into eccentric orbits, dipping down to the planet's cloud top and back again. At 60,000km away from that cloud top, chunks will be accelerating up to 20km/s when hitting the atmosphere... keeping in mind that the US Space Shuttle Orbiter's safe deorbit speed was 7.8km/s and needed special heat shields to keep from disintegrating.
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askscience
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The larger rings are often formed from the same cloud that formed the planet, so they start out with the same - or at least a very similar - angular momentum, which means that they share the rotational axis of the planet.
Theoretically, a ring can also be accumulated over time from material foreign to the planet itself, and might not necessarily be aligned to the axis, but given that most of the material that could realistically form a ring (instead of orbiting asteroids or small moons) originated in the solar system, it is likely that all rings that can exist already exist, and share the solar system plane.
[edit] Except for Planet "It's not a phase mom!" Uranus.
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askscience
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Another thing others haven't mentioned is conservation of angular momentum. Imagine you have two identical rocks spinning in opposite directions at same speeds. If they were to collide and merge they will form a bigger rock with exactly zero spin. In general, whenever two objects collide the "amount they spin" (called angular momentum - which depends on their mass, shape, speed and directron of rotation) always stays the same.
So if you have a giant cloud of rocks orbiting a planet that keep colliding and tending towards rings, the total (sum) angular momentum of the final rings will equal the sum of the angular momentums in the original cloud. So if the cloud is rotating along the same axis as the planet (which they usually do, as the planet and the rings-to-be are usually created from a single, bigger pile of stuff), the rings will to.
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askscience
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Fun fact: collisions are the go to answer for most wonky things in the universe.
Why does Uranus have a weird tilt? It was hit with a big rock.
Why does venus rotate backwards? It was hit with a big rock.
Why are there rings around gas giants inside of and orb of debris? A bunch of small rocks hitting each other.
Why is the solar system flat? A bunch of big rocks smashing into each other.
Why does the earth have a large moon relative to its size? It was hit with a large rock.
Why is Mars lopsided? You guessed it... big rock.
Granted, this is a little over simplified, but whenever something new is discovered, it's almost a knee jerk reaction to ask if it can be explain by a collision, by a bunch of collisions or by an even bigger collision.
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askscience
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No, those would not be dynamically stable and therefore decay until only the net angular momentum was left, ie. in just one direction of rotation.
What would cause the dynamic instability to decay? The same kinds of events that cause the ring in the first place and continue to happen in our own solar system still. Nearby planets and their passes and alignments, solar wind and radiation intensities, and tidal forces from whatever major bodies the rings are orbiting will decay the momentum of the ring bodies, at different rates. Any body that loses energy more than others spirals inwards toward the parent mass. That would make bodies pass through counter-revolving belts and rapidly destroy them until only net angular momentum was left.
There's actually bunch of other interesting mechanism that would bleed out that imbalance, but the bigger picture that probably helps understand better is that a system with total component angular momentum much larger than net momentum is inherently dynamically unstable (eqv to not being in lowest energy state), and a whole host of secondary and tertiary mechanisms that are available to it to decay energy states will ALSO end up decaying its total angular momentum till its closer to its lowest state.
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