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And we're going to go into a lot more detail. Synthesis. And as the word implies, photo, it's photosynthesis, it's making things out of light. And one thing I like to ask people when they are first exposed to photosynthesis, I was like, okay, we could see this grass growing, or we could see this wheat growing, or we co... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
And one thing I like to ask people when they are first exposed to photosynthesis, I was like, okay, we could see this grass growing, or we could see this wheat growing, or we could see a tree growing, but where is that material coming from? And the most common answer is, oh, somehow it's coming from the ground, and the... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
But you have carbon dioxide primarily in the air. So you have carbon, you have, I'll just write it this way. So you have carbon dioxide in the air. And what photosynthesis allows these plants to do is take the carbon and that carbon dioxide and form bonds with it, turn it from its gas form into solid forms, into glucos... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
And what photosynthesis allows these plants to do is take the carbon and that carbon dioxide and form bonds with it, turn it from its gas form into solid forms, into glucose molecules, and then use that glucose to build up cellulose and to build out other forms of starch and whatever else it might be. So it's taking th... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
Now, from there, other living organisms, and this is a huge oversimplification, it can involve bacteria, it can involve all sorts of things. And just a reminder, even on that photosynthesis, it isn't just light and it isn't just the carbon dioxide, it also involves the water, and we talk about that. So you also have wa... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
You also have the water involved. So you have the carbon dioxide, so CO2, light from the sun, and water. These things are able to grow, and nutrients from the earth. And then from that, you're able to construct things like, well, you can directly go to these plants that are taking energy from the sun and construct thin... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
And then from that, you're able to construct things like, well, you can directly go to these plants that are taking energy from the sun and construct things like bread. Or you have other animals that will eat things like the grass and then break them down in their own way, and they'll be assisted by bacteria, and then ... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
It's able to break it down, it's able to catabolize the various molecules in the grass and break them down into building blocks that can then be used to build up the cow, to build up milk, and whatever else. And you might be saying, what are these types of molecules that we keep breaking down and then building back up?... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
Carbohydrates. And you're going to see most of the molecules that I'm about to talk about, frankly, all of them on the back of a nutritional package, because it tells you what's inside of it. What is your body going to metabolize when it eats that whatever's inside of the package? So carbohydrates, these are either sim... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
So carbohydrates, these are either simple sugars like glucose or fructose, or it could be polymers of the sugars, polysaccharides. It could be starches made up of many, many elements, or many, many multiples of these simple sugars. We could be talking about lipids. So fatty acids, we could be talking about cholesterols... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
So fatty acids, we could be talking about cholesterols. These are essential structures, and they're also essential for various metabolic pathways inside of all of life. Or it could be proteins. It could be proteins made up of amino acids. Sometimes people say, the reason why you want the proteins is because it's made u... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
It could be proteins made up of amino acids. Sometimes people say, the reason why you want the proteins is because it's made up of these amino acids. So you could break down these proteins and get the amino acids, and then build it up into new proteins. Proteins and amino acids. And all of these things, they are found ... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
Proteins and amino acids. And all of these things, they are found in things like in the foods we eat, which we will then consume. We will then metabolize. We will first catabolize them and break them down, and then we will use those building blocks to build it back up. And at the end of the day, these provide the struc... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
We will first catabolize them and break them down, and then we will use those building blocks to build it back up. And at the end of the day, these provide the structures that make our bodies what they are. They allow us to interact with our environment, and they provide energy. And that energy, at the end of the day, ... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
And that energy, at the end of the day, the true molecular currency for that energy is a molecule called ATP. That's a molecule of ATP right over there. Adenosine triphosphate. And the key for ATP, why it is the molecular currency for energy, are the three phosphate groups. So it has these three phosphate groups, and w... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
And the key for ATP, why it is the molecular currency for energy, are the three phosphate groups. So it has these three phosphate groups, and we have a whole video on it, or a whole series of videos on it, really. But the main key is that there's a lot of energy, especially between the, I guess on the last phosphate gr... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
And this energy in that bond, as the phosphate group breaks off, it can release it to provide all sorts of life mechanisms, including being able to metabolize things. So ATP right over here, this is the currency of energy in life as we know it. And it's actually an interesting molecule because it's essentially, it's a ... | Introduction to metabolism anabolism and catabolism Khan Academy.mp3 |
What I want to do in this video is think a little bit more about how populations can be regulated. And broadly speaking, we can think of the regulation of populations in two different categories. There's the regulation dependent on density, so density dependent regulation, density dependent, and then there's the type o... | Population regulation Ecology Khan Academy.mp3 |
Independent, independent regulation. So first let's think about density dependent regulation. And let me draw a little chart here to help us visualize that. So let's say that that axis is the population. I'll say P for population. And let's say this axis is time, so T for time. In previous videos, we talked about a pop... | Population regulation Ecology Khan Academy.mp3 |
So let's say that that axis is the population. I'll say P for population. And let's say this axis is time, so T for time. In previous videos, we talked about a population, I like to use the example of rabbits, how it could grow exponentially. So if it's just growing a certain percent every month, that population will g... | Population regulation Ecology Khan Academy.mp3 |
In previous videos, we talked about a population, I like to use the example of rabbits, how it could grow exponentially. So if it's just growing a certain percent every month, that population will grow exponentially. But we can't expect that that will just happen forever. If rabbits just kept growing exponentially, it ... | Population regulation Ecology Khan Academy.mp3 |
If rabbits just kept growing exponentially, it wouldn't take long for them to cover the surface of the Earth and then fill the universe, if in some ways they weren't limited by anything. But we know that they are limited by things. And so the environment only has a certain amount of carrying capacity. And we'll think a... | Population regulation Ecology Khan Academy.mp3 |
And we'll think a little bit about this carrying capacity in a second. And what's determining the carrying capacity. And so as the density of the rabbits in a certain area get higher and higher and higher, well then the density dependent, let me use a different color, the density dependent factors start to play. The de... | Population regulation Ecology Khan Academy.mp3 |
The density dependent limiting factors. And what could be some of these density dependent limiting factors that keep the population from going dramatically above the carrying capacity? Well, the most obvious one could be competition for resources competition for resources. And the one that might come to mind most clear... | Population regulation Ecology Khan Academy.mp3 |
And the one that might come to mind most clearly is food resources. So this is actually a picture of Australia in the mid 1800s. And they had a bunny population problem. That rabbits were first introduced in order to have a little bit of hunting. But then they reproduced like rabbits. And it was estimated that at some ... | Population regulation Ecology Khan Academy.mp3 |
That rabbits were first introduced in order to have a little bit of hunting. But then they reproduced like rabbits. And it was estimated that at some point you had over a billion rabbits that had populated the country. And that was, you might say, oh how cute. But it was a huge problem. They were eating all of the, the... | Population regulation Ecology Khan Academy.mp3 |
And that was, you might say, oh how cute. But it was a huge problem. They were eating all of the, they were eating the farmable, they were eating crops, they were eating the grass that other types of livestock would graze on. So it was a huge infestation of rabbits. And so you can imagine one competition for resources ... | Population regulation Ecology Khan Academy.mp3 |
So it was a huge infestation of rabbits. And so you can imagine one competition for resources is just the grass itself. In this picture you can see that the land is barren. Maybe this happened because the rabbits ate all of the vegetation here. So competition for resources. One type of resource could be food. Another t... | Population regulation Ecology Khan Academy.mp3 |
Maybe this happened because the rabbits ate all of the vegetation here. So competition for resources. One type of resource could be food. Another type of resource could be water. There might only be so much water to support organisms of a certain kind. And we're only, here we often talk about animals, but it could be p... | Population regulation Ecology Khan Academy.mp3 |
Another type of resource could be water. There might only be so much water to support organisms of a certain kind. And we're only, here we often talk about animals, but it could be plants, or it could be bacteria. It could be all sorts of organisms that we're talking about. And if we're talking about plants, we could t... | Population regulation Ecology Khan Academy.mp3 |
It could be all sorts of organisms that we're talking about. And if we're talking about plants, we could think about light. You could say, well what limits having an infinite number of plants in a certain area? Well, water will limit. The nutrients in the soil will limit. But also access to light. You've seen pictures ... | Population regulation Ecology Khan Academy.mp3 |
Well, water will limit. The nutrients in the soil will limit. But also access to light. You've seen pictures of a dense canopy in a rainforest. And the plants are trying to seek out whatever gap in the canopy they can find so that they can get some access to that light. Now there's other examples, and this wouldn't app... | Population regulation Ecology Khan Academy.mp3 |
You've seen pictures of a dense canopy in a rainforest. And the plants are trying to seek out whatever gap in the canopy they can find so that they can get some access to that light. Now there's other examples, and this wouldn't apply as much to, say, plants, but the idea of shelter. This might apply to humans, or to o... | Population regulation Ecology Khan Academy.mp3 |
This might apply to humans, or to other types of animals that maybe need shelter in order to hide, or a place to reproduce, or whatever else. So at some point, if the population density gets too high in a certain region, then these things are going to limit how dense the population can get, or frankly, just what the po... | Population regulation Ecology Khan Academy.mp3 |
And it is possible that you could even go above the carrying capacity, and then you're kind of this very unstable situation, and then something happens, you go below it, then you go above it, and then below it, and then something like that. But what are other density-dependent factors that we could think about? Well, a... | Population regulation Ecology Khan Academy.mp3 |
And so predatory factors, or we could say predation. Predation. Once a population gets large enough and dense enough, it might be the predators who could say, hey, we can start, it's way easier for us to get our lunch. Now, the other thing, that it might be a little less obvious, but when you have a high-density popula... | Population regulation Ecology Khan Academy.mp3 |
Now, the other thing, that it might be a little less obvious, but when you have a high-density population, and there's examples of this in medieval times in Europe, and even in modern times today with human populations, but this happens with all organisms, is that when you become a dense population, there's more intera... | Population regulation Ecology Khan Academy.mp3 |
The thing that always comes to my mind is the plague in medieval times, where it was very easy to spread from one human to the next, or frankly, from rats to humans, and whatever else. Now, the other thing, and this is maybe somewhat related to everything else we've talked about, is waste accumulation. So let me write ... | Population regulation Ecology Khan Academy.mp3 |
Waste. If you have a really high-density population, and the waste is just everywhere, it could poison the water, it might poison sources of food, it might help the spread of disease and parasites. And once again, all of these things help define what the carrying capacity, how dense can a population get in a certain re... | Population regulation Ecology Khan Academy.mp3 |
Now, you might say, well, maybe they don't have to stay in a region, maybe they can go and explore other places, and that's possible, and that's been the story for many different types of species. Lemmings are famous for when their population gets dense in a certain area, groups of them start just running to start expl... | Population regulation Ecology Khan Academy.mp3 |
They're related to other living things around. The density-independent factors tend to be abiotic, they tend to not be related to living things. So the most common density-independent factor is natural disasters. So natural, natural disaster. We have a picture here of a forest fire. The deer population here might not b... | Population regulation Ecology Khan Academy.mp3 |
So natural, natural disaster. We have a picture here of a forest fire. The deer population here might not be in any way close to their carrying capacity, but despite that, the forest fire maybe might kill off a lot of the deer. Other natural disasters, you could have a flood, you could have a tsunami, you could have a ... | Population regulation Ecology Khan Academy.mp3 |
Other natural disasters, you could have a flood, you could have a tsunami, you could have a meteorite coming from outer space, that happened to the dinosaurs, to just knock out huge populations. And so density-independent factors, you could have the population growing, and at just some random point, there's some densit... | Population regulation Ecology Khan Academy.mp3 |
Who knows? But the density-independent factors, once again, it's not related to where we are on this curve. It could happen at any time, and to some degree, they feel a little bit more random. Now, with all of this talk about carrying capacities and the different density-dependent factors, you might be thinking, well, ... | Population regulation Ecology Khan Academy.mp3 |
In this video, we're going to explore membrane proteins. Did you know that the cell membrane can be composed up to 75% protein? So most cell membranes have about 50% or less protein. And proteins are there because the cell membrane uses proteins for pretty much everything that it does, all of these cell membrane proces... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
And proteins are there because the cell membrane uses proteins for pretty much everything that it does, all of these cell membrane processes that it performs. So just to remind us what a cell membrane actually is, a cell membrane is made up of little things that look like this, which are called phospholipids. And they ... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
So over here, I've pre-drawn a lipid bilayer. And it'll look something like this. It'll be made up of a lot of these small phospholipids that we've drawn above. And it'll make up our bilayer. So you can see that there are two layers of these phospholipids. Now, there's two major types of proteins in the cell membrane. ... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
And it'll make up our bilayer. So you can see that there are two layers of these phospholipids. Now, there's two major types of proteins in the cell membrane. The first can look something like this. And this can appear anywhere in the cell membrane. And there are usually quite a few of these throughout the entire cell.... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
The first can look something like this. And this can appear anywhere in the cell membrane. And there are usually quite a few of these throughout the entire cell. So this is what we call an integral protein. You'll notice that it's called an integral protein because you can think of it like it's integrated throughout th... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
So this is what we call an integral protein. You'll notice that it's called an integral protein because you can think of it like it's integrated throughout the entire membrane. Another type of protein that we might encounter might appear on top of the membrane. Occasionally, it might be slightly into the membrane. And ... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
Occasionally, it might be slightly into the membrane. And it can also rest on top of integral proteins. And this we call peripheral proteins. And the reason why we call it a peripheral protein is because it's on the peripheral, or the outside, of the cell membrane. The difference between peripheral and integral protein... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
And the reason why we call it a peripheral protein is because it's on the peripheral, or the outside, of the cell membrane. The difference between peripheral and integral proteins is that integral proteins are really stuck inside the cell membrane. As you can see in this picture, the integral protein is really inside t... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
And as a result, it'll be very difficult to remove. Peripheral proteins kind of attach and remove themselves from the cell membrane or from other proteins. They generally are there for different cell processes. So for example, a hormone might be a peripheral protein. And it might attach to the cell, make the cell do so... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
So for example, a hormone might be a peripheral protein. And it might attach to the cell, make the cell do something, and then leave. Peripheral proteins can also exist inside the cell on the cell membrane. Another type of protein is extremely rare. And it can appear inside the cell membrane like that. And we call this... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
Another type of protein is extremely rare. And it can appear inside the cell membrane like that. And we call this a lipid-bound protein. Why might you think a lipid-bound protein is so difficult to find, so rare? Well, the reason why is because proteins are there to interact with the outside environment. And lipid-boun... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
Why might you think a lipid-bound protein is so difficult to find, so rare? Well, the reason why is because proteins are there to interact with the outside environment. And lipid-bound proteins are stuck on the interior of the cell membrane itself. So it can't really interact with the outside of the cell or the inside ... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
So it can't really interact with the outside of the cell or the inside of the cell. So it doesn't really serve a big function in terms of the cell membrane performing its duties. We're going to spend a little bit of time talking about two types of integral proteins that are extremely important, because these two protei... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
And they help the cell maintain homeostasis, or balance. The first type can look something like this. Again, this is an integral protein. What do you think this protein might be used for? This isn't two proteins. It's actually one protein with a hole through it. Well, this protein is actually used to allow things to pa... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
What do you think this protein might be used for? This isn't two proteins. It's actually one protein with a hole through it. Well, this protein is actually used to allow things to pass through the cell. We call this a channel protein. And like the name implies, there's a channel or hole inside the protein that lets thi... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
Well, this protein is actually used to allow things to pass through the cell. We call this a channel protein. And like the name implies, there's a channel or hole inside the protein that lets things pass through. So for example, if there is some sort of ion, let's say this is an Na plus ion, a sodium ion, this is outsi... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
So for example, if there is some sort of ion, let's say this is an Na plus ion, a sodium ion, this is outside the cell. And the cell at this point really needs these sodium ions to perform a really important process. So what the channel proteins do is they'll allow these outside extracellular ions into the cell. And no... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
And normally, these sodium ions wouldn't be able to pass through the cell membrane just by themselves. These channel proteins allow our bodies to take in different materials from the outside environment into our cells. What they can also do is they can also do the reverse. So let's say your cell has way too much sodium... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
So let's say your cell has way too much sodium, and it needs to get rid of it. So channel proteins can start pumping these out. Channel proteins generally don't require energy. So there's no energy needed. Sometimes we call energy ATP. And another thing that's special about channel proteins is you'll notice that it'll ... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
So there's no energy needed. Sometimes we call energy ATP. And another thing that's special about channel proteins is you'll notice that it'll go with the concentration gradient. So out here, there's a lot. And inside, there's very little. So it'll pump from where there's a lot of sodium into where there's very little.... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
So out here, there's a lot. And inside, there's very little. So it'll pump from where there's a lot of sodium into where there's very little. So it'll go what we call down a concentration gradient. Concentration gradient. The second type of very important integral protein is called a carrier protein. And like the name ... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
So it'll go what we call down a concentration gradient. Concentration gradient. The second type of very important integral protein is called a carrier protein. And like the name implies, it carries substances into the cell. I kind of picture it like a baseball glove, like this. So if there's a molecule that's outside t... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
And like the name implies, it carries substances into the cell. I kind of picture it like a baseball glove, like this. So if there's a molecule that's outside the cell, and the cell actually needs this molecule, so what the carrier protein will do is it'll actually protect this substance so that it can enter the cell s... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
It can also do this in reverse. It can take something inside the cell and pump it outside the cell. And this type of protein is really important because unlike channel proteins, carrier proteins can go against the concentration gradient. And this is really important because say your cell has a lot of chloride ions. And... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
And this is really important because say your cell has a lot of chloride ions. And your body needs more to perform a certain process. So what your body can do is it can bring more chloride ions into your cell, even though your cell already has a lot of chloride ions. So carrier proteins can sometimes use energy or ATP.... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
So carrier proteins can sometimes use energy or ATP. Finally, there's a type of protein that can exist on any of these that we've drawn here. And this is what we call a glycoprotein. So what a glycoprotein would look like is there will be a chain of sugars attached to a protein. And it can be on integral proteins, peri... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
So what a glycoprotein would look like is there will be a chain of sugars attached to a protein. And it can be on integral proteins, peripheral proteins, channel proteins. Glycoproteins, you'll notice, have the prefix glyco, which means sugar. And basically, it's just sugar plus protein. And the purpose of glycoprotein... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
And basically, it's just sugar plus protein. And the purpose of glycoproteins is that it's used in signaling. So it allows a cell to recognize another cell. So in summary, in this picture that we have drawn out of a cell membrane and several different proteins, we have two main classes of proteins. We have peripheral p... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
So in summary, in this picture that we have drawn out of a cell membrane and several different proteins, we have two main classes of proteins. We have peripheral proteins, which are on the outside of the cell. And they're really easy to remove. We have our integral proteins, which are stuck inside the cell and really t... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
We have our integral proteins, which are stuck inside the cell and really tough to remove. We have our lipid-bound proteins. We have channel proteins, which allow things to move through the cell by its concentration gradient. And it doesn't require energy. And it doesn't require ATP. We have our carrier proteins, which... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
And it doesn't require energy. And it doesn't require ATP. We have our carrier proteins, which are kind of like a baseball glove. It can take in a particular molecule and let it out inside the cell. Or it can do it in reverse. And these can sometimes use ATP. And what's special is they can go against the concentration ... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
It can take in a particular molecule and let it out inside the cell. Or it can do it in reverse. And these can sometimes use ATP. And what's special is they can go against the concentration gradient. And finally, we have glycoproteins, which really can be any of the proteins that we've drawn out. It's a sugar plus a pr... | Cell membrane proteins Cells MCAT Khan Academy.mp3 |
Species go extinct for a variety of natural reasons like meteor strikes, volcanic eruptions, natural climate shifts, movements of continents over geological eons, things that occur all the time without the involvement of humans. Therefore, scientists know there's a natural background rate of extinction that's estimated... | Biodiversity and extinction, then and now.mp3 |
Some can deal with it, others can't. A major change has the potential result of an extinction. Even without a direct natural phenomenon that could kill individuals directly, a species could go extinct due to its inability to keep up with the competitors, predators, or parasites that are always influencing its local env... | Biodiversity and extinction, then and now.mp3 |
It's now estimated that the present extinction rate is somewhere between 1,000 to 10,000 times the background rate. And we also know the main reason for this. The reason is us. What I'd like to do here is frame this within nothing less than the entire history of life on Earth. Have extinctions of this magnitude happene... | Biodiversity and extinction, then and now.mp3 |
What I'd like to do here is frame this within nothing less than the entire history of life on Earth. Have extinctions of this magnitude happened before? And what can we learn from that? The answer is yes. There have been massive extinctions in the past, and we're now experiencing the highest rate of extinction since th... | Biodiversity and extinction, then and now.mp3 |
The answer is yes. There have been massive extinctions in the past, and we're now experiencing the highest rate of extinction since the last major mass extinction that occurred at the end of the Cretaceous, some 65 million years ago. This is the one that a lot of people, especially seven-year-olds, are familiar with be... | Biodiversity and extinction, then and now.mp3 |
This extinction was likely caused by effects that occurred after the impact of a large asteroid, which scientists like to call a bolide. So when you see the term bolide impact, you can tell your friends that that means basically kablooey. Some suggest that the smoking gun of this bolide impact is a huge crater 15 to 20... | Biodiversity and extinction, then and now.mp3 |
This crater was made by a bolide about 10 kilometers across. Events like this leave a physical, detectable mark in Earth's crust. Geologists use markers like this, along with other changes in the rocks, to give special names to specific periods, intervals of geologic time and history bounded by these markers. Names lik... | Biodiversity and extinction, then and now.mp3 |
Names like Paleozoic, Cambrian, Carboniferous, Cenozoic, these are names of epochs, eras, periods, etc. in the history of the planet. Scientists ask if we are, right now, making an event that will be detectable millions of years from now in the geologic record. Some claim that we are, and that we should be calling this... | Biodiversity and extinction, then and now.mp3 |
Some claim that we are, and that we should be calling this present epoch the Anthropocene. Anthro for human, with cene being the suffix that we use to designate these epochs. So these scientists suggest that we signify a special epoch in the history of the Earth, an epoch marked by a new type of fossil evidence, such a... | Biodiversity and extinction, then and now.mp3 |
Right now, what can we learn from the past by looking at this big picture history of extinction on Earth? We know that biodiversity is governed by a balancing act between speciation and extinction. Does biodiversity increase steadily with time? Has it reached an equilibrium limit? Speciation is caused by one species sp... | Biodiversity and extinction, then and now.mp3 |
Has it reached an equilibrium limit? Speciation is caused by one species splitting to give rise to two new species, each of those giving rise to two more, and so on. You'd expect the number of species to increase over time. However, that multiplication is offset by extinction. If you look at a graph of biodiversity ove... | Biodiversity and extinction, then and now.mp3 |
However, that multiplication is offset by extinction. If you look at a graph of biodiversity over the history of our planet, you get something that looks like this. You can see that there is indeed an overall trend towards an increase in biodiversity, but you can also mark certain spots on this curve here, here, here, ... | Biodiversity and extinction, then and now.mp3 |
These are known as major mass extinction events, times during which extraordinarily high numbers of species disappeared, times when the extinction rate was well above the background rate. It's worth looking at these because they suggest some interesting and, I think, relevant reasons for why these extinctions happen. S... | Biodiversity and extinction, then and now.mp3 |
The first one, here, occurs at the Ordovician-Selurian boundary 440 to 450 million years ago. What on Earth can we learn from something that happened so long ago? Well, for one thing, during this time, 60% of marine invertebrate species died out. These extinctions seem to be the result of effects caused by movement of ... | Biodiversity and extinction, then and now.mp3 |
These extinctions seem to be the result of effects caused by movement of the huge supercontinent that existed at that time, Gondwana. Sounds like a pretty interesting place, except that it moves slowly into the south polar region, with a consequent sea level fall as significant amounts of the planet's precipitation bec... | Biodiversity and extinction, then and now.mp3 |
The second major extinction, here, occurred during the late Devonian period, about 374 million years ago. I'm amazed that scientists can get that precise, but they can. We now know that 50% of all the genera on Earth went extinct at this time. Think about that for a moment. We're not talking about species, we're talkin... | Biodiversity and extinction, then and now.mp3 |
Think about that for a moment. We're not talking about species, we're talking about entire genera. And that means a lot of species. There's some thought that this was due to a bolide impact that occurred long before the one that wiped out the dinosaurs. But maybe not. Others think maybe it was oceanic volcanism, or som... | Biodiversity and extinction, then and now.mp3 |
There's some thought that this was due to a bolide impact that occurred long before the one that wiped out the dinosaurs. But maybe not. Others think maybe it was oceanic volcanism, or some global cooling mechanism that we don't fully understand. Some suggest that it was due to a drop in speciation rate, rather than an... | Biodiversity and extinction, then and now.mp3 |
Some suggest that it was due to a drop in speciation rate, rather than an increase in extinction rate. And clearly, more research is needed here. The third of the big five extinction events, here, is something that occurred at the end of the Permian, between the Permian and Triassic periods, about 252 million years ago... | Biodiversity and extinction, then and now.mp3 |
This is sometimes known as the Great Dying, the biggest known extinction event, during which 96% of all marine and 70% of all terrestrial vertebrates died out. It also appears that it's one of the few mass extinctions in which insects took a big hit. I guess it takes a lot to kill all those cockroaches. In total, 83% o... | Biodiversity and extinction, then and now.mp3 |
In total, 83% of all the genera on Earth disappeared. The suggested reasons behind this mass extinction range all over the map, some people think it might have been one or more bolide impacts, or volcanism on a huge scale, possibly from a place called the Siberian Traps, where there were huge outpourings of lava, big f... | Biodiversity and extinction, then and now.mp3 |
Methane can be stored by the activities of bacteria as something called methane clathrates in sediments of the ocean floor. Geologic disturbance might be able to release these stores of clathrates, releasing huge amounts of the potent greenhouse gas, methane. Other people think that there might have been major sea leve... | Biodiversity and extinction, then and now.mp3 |
Increasing anoxic conditions, or lack of oxygen in the deep sea, or perhaps shifts in oceanic circulation patterns could be results of those climate changes. Or maybe a hellish convergence of all these things. I can easily imagine the volcanism causing earthquakes that would release methane clathrates and cause oceanic... | Biodiversity and extinction, then and now.mp3 |
A cascade of disasters. The fourth major extinction occurred at the Triassic-Jurassic boundary, 201 million years ago. 34% of all marine genera died out, along with a whole bunch of terrestrial vertebrate groups, clearing the stage for the rise of the dinosaurs. Hooray! Where would all of our 5-10 year olds be if it we... | Biodiversity and extinction, then and now.mp3 |
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