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mirror with just the right shape to collect and focus the light into a sharp image. Figure 6.9. Thirty-Six Eyes Are Better Than One. The mirror of the 10-meter Keck telescope is composed of 36 hexagonal sections. (credit: NASA Learn more about the Keck Observatory on Mauna Kea (https://openstaxcollege.org/l/ 30KeckObs... |
a larger telescope than the one at Lick. One prospective donor was Charles T. Yerkes, who, among other things, ran the trolley system in Chicago. Hale wrote to Yerkes, encouraging him to support the construction of the giant telescope by saying that “the donor could have no more enduring monument. It is certain that M... |
1926, he wrote an article in Harper’s Magazine about the scientific value of a still larger telescope. This article came to the attention of the Rockefeller Foundation, which granted $6 million for the construction of a 200-inch telescope. Hale died in 1938, but the 200-inch (5-meter) telescope on Palomar Mountain was... |
in blurred star images. Astronomers call these effects “bad seeing.” When seeing is bad, images of celestial objects are distorted by the constant twisting and bending of light rays by turbulent air. The best observatory sites are therefore high, dark, and dry. The world’s largest telescopes are found in such remote m... |
Astronomers are always eager to make out more detail in the images they study, whether they are following the weather on Jupiter or trying to peer into the violent heart of a “cannibal galaxy” that recently ate its neighbor for lunch. One factor that determines how good the resolution will be is the size of the telesc... |
the middle of an ocean. Air that has flowed long distances over water before it encounters land is especially stable. This OpenStax book is available for free at http://cnx.org/content/col11992/1.8 Chapter 6 Astronomical Instruments 205 The resolution of an image is measured in units of angle on the sky, typically in ... |
opes In the popular view (and some bad movies), an astronomer spends most nights in a cold observatory peering through a telescope, but this is not very accurate today. Most astronomers do not live at 206 Chapter 6 Astronomical Instruments observatories, but near the universities or laboratories where they work. An ast... |
ribe how a spectrometer works After a telescope collects radiation from an astronomical source, the radiation must be detected and measured. The first detector used for astronomical observations was the human eye, but it suffers from being connected to an imperfect recording and retrieving device—the human brain. Photo... |
the sky has looked like during the past 100 years. Photography represents a huge improvement over the human eye, but it still has limitations. Photographic films are inefficient: only about 1% of the light that actually falls on the film contributes to the chemical change that makes the image; the rest is wasted. Astr... |
much greater heat radiated by the telescope itself and our planet’s atmosphere. Typical temperatures on Earth’s surface are near 300 K, and the atmosphere through which observations are made is only a little cooler. According to Wien’s law (from the chapter on Radiation and Spectra), the telescope, the observatory, an... |
, the image of a source produced by the telescope) enters the instrument through a small hole or narrow slit, and is collimated (made into a beam of parallel rays) by a lens. The light then passes through a prism, producing a spectrum: different wavelengths leave the prism in different directions because each wavelengt... |
first source of cosmic radio waves. Figure 6.17. First Radio Telescope. This rotating radio antenna was used by Jansky in his serendipitous discovery of radio radiation from the Milky Way. In 1936, Grote Reber, who was an amateur astronomer interested in radio communications, used galvanized iron and wood to build the... |
on a visible-light or infrared telescope, providing information about how much radiation we receive at each wavelength or frequency. After computer processing, the radio signals are recorded on magnetic disks for further analysis. Radio waves are reflected by conducting surfaces, just as light is reflected from a shin... |
ll Telescope Canberra Deep Space Communication Complex (CDSCC) Goldstone Deep Space Communications Complex (GDSCC) Bonn, Germany 100-m steerable dish www.mpifr-bonn.mpg.de/en/ effelsberg Manchester, England Tidbinbilla, Australia 76-m steerable dish www.jb.man.ac.uk/aboutus/ lovell 70-m steerable dish www.cdscc.nasa.go... |
IRAM Granada, Spain 30-m steerable mmwave dish www.iram-institute.org James Clerk Maxwell Telescope (JCMT) Mauna Kea, HI 15-m steerable mmwave dish www.eaobservatory.org/jcmt Nobeyama Radio Observatory (NRO) Minamimaki, Japan 6-element array of 10-m wave dishes www.nro.nao.ac.jp/en Hat Creek Radio Observatory (HCRO) C... |
sky together. Computer processing of the results permits the reconstruction of a high-resolution radio image. The most extensive such instrument in the United States is the National Radio Astronomy Observatory’s Very Large Array (VLA) near Socorro, New Mexico. It consists of 27 movable radio telescopes (on railroad tr... |
the Virgin Islands to Hawaii (Figure 6.21). The VLBA, completed in 1993, can form astronomical images with a resolution of 0.0001 arcseconds, permitting features as small as 10 astronomical units (AU) to be distinguished at the center of our Galaxy. Figure 6.21. Very Long Baseline Array. This map shows the distributio... |
Mercury, Venus, Mars, and the large moons of Jupiter. Any radio dish can be used as a radar telescope if it is equipped with a powerful transmitter as well as a receiver. The most spectacular facility in the world for radar astronomy is the 1000-foot (305-meter) telescope at Arecibo in Puerto Rico (Figure 6.22). The A... |
the ground as well as for launching into space. Airborne and Space Infrared Telescopes Water vapor, the main source of atmospheric interference for making infrared observations, is concentrated in the lower part of Earth’s atmosphere. For this reason, a gain of even a few hundred meters in elevation can make an import... |
of less than 10 K. For the first time, the infrared sky could be seen as if it were night, rather than through a bright foreground of atmospheric and telescope emissions. IRAS carried out a rapid but comprehensive survey of the entire infrared sky over a 10-month period, cataloging about 350,000 sources of infrared ra... |
discuss in the chapters on Galaxies). HST is operated jointly by NASA’s Goddard Space Flight Center and the Space Telescope Science Institute in Baltimore. It was the first orbiting observatory designed to be serviced by Shuttle astronauts and, over the years since it was launched, they made several visits to improve ... |
orbit. The telescope now works as it was intended to, and further missions to it were able to install even more advanced instruments to take advantage of its capabilities. High-Energy Observatories Ultraviolet, X-ray, and direct gamma-ray (high-energy electromagnetic wave) observations can be made only from space. Suc... |
made from Earth’s surface by using the atmosphere as the primary detector. When a gamma ray hits our atmosphere, it accelerates charged particles (mostly electrons) in the atmosphere. Those energetic particles hit other particles in the atmosphere and give off their own radiation. The effect is a cascade of light and ... |
of the universe and to see them more clearly. The premier space facility planned for the next decade is the James Webb Space Telescope (Figure 6.27), which (in a departure from tradition) is named after one of the early administrators of NASA instead of a scientist. This telescope will have a mirror 6 meters in diamet... |
think what this means: 30 meters is one-third the length of a football field. It is technically impossible to build and transport a single astronomical mirror that is 30 meters or larger in diameter. The primary mirror of these giant telescopes will consist of smaller mirrors, all aligned so that they act as a very la... |
images aperture diameter of the primary lens or mirror of a telescope charge-coupled device (CCD) array of high-sensitivity electronic detectors of electromagnetic radiation, used at the focus of a telescope (or camera lens) to record an image or spectrum chromatic aberration distortion that causes an image to appear ... |
and support large mirrors because the light does not have to pass through glass. 6.2 Telescopes Today New technologies for creating and supporting lightweight mirrors have led to the construction of a number of large telescopes since 1990. The site for an astronomical observatory must be carefully chosen for clear wea... |
to measure very energetic gamma rays. Astronomers are building the LSST to observe with an unprecedented field of view and a new generation of visible-light/infrared telescopes with apertures of 24.5 to 39 meters in diameter. This OpenStax book is available for free at http://cnx.org/content/col11992/1.8 Chapter 6 Ast... |
Galaxies Viewed in Full Spectrum of Light: https://www.youtube.com/watch?v=368K0iQv8nE. Scientists with the Spitzer Observatory show how a galaxy looks different at different wavelengths (6:22) Lifting the Cosmic Veil: Highlights from a Decade of the Spitzer Space Telescope: https://www.youtube.com/ watch?v=nkrNQcwkY7... |
, who want to save some clear channels for doing astronomy, and the companies that stand to make a lot of money from expanding cellular phone use. What arguments would sway you to each side? F. When the site for the new Thirty-Meter Telescope on Hawaii’s Mauna Kea was dedicated, a group of native Hawaiians announced op... |
amount of time? 6. What is meant by “reflecting” and “refracting” telescopes? 7. Why are the largest visible-light telescopes in the world made with mirrors rather than lenses? 8. Compare the eye, photographic film, and CCDs as detectors for light. What are the advantages and disadvantages of each? 9. What is a charge... |
site? Don’t forget practical ones. Should astronomers, for example, consider building an observatory on Denali (Mount McKinley) or Mount Everest? 230 Chapter 6 Astronomical Instruments 22. Suppose you are looking for sites for a visible-light observatory, an infrared observatory, and a radio observatory. What are the ... |
how much light is lost by such an arrangement. The primary mirror (the one at the bottom in Figure 6.6) of the Gemini North telescope is 8 m in diameter. The secondary mirror at the top is about 1 m in diameter. Use the formula for the area of a circle to estimate what fraction of the light is blocked by the secondary... |
camera on the rover’s extended mast, so that the many positions of the mast (which acted like a selfie stick) are edited out. (credit: modification of work by NASA/JPL-Caltech/MSSS) Chapter Outline 7.1 Overview of Our Planetary System 7.2 Composition and Structure of Planets 7.3 Dating Planetary Surfaces 7.4 Origin of... |
and a small fraction of the material in the outer parts eventually formed the other objects. During the past 50 years, we have learned more about the solar system than anyone imagined before the space age. In addition to gathering information with powerful new telescopes, we have sent spacecraft directly to many membe... |
ball about 1.4 million kilometers in diameter, with surface layers of incandescent gas and an interior temperature of millions of degrees. The Sun will be discussed in later chapters as our first, and best-studied, example of a star. Mass of Members of the Solar System Object Percentage of Total Mass of Solar System S... |
discussed further in the chapter on Rings, Moons, and Pluto). To date, more than 1750 of these TNOs have been discovered. This OpenStax book is available for free at http://cnx.org/content/col11992/1.8 Chapter 7 Other Worlds: An Introduction to the Solar System 237 Figure 7.3. Orbits of the Planets. All eight major pl... |
name for Jupiter in mythology) or giant planets—a name they richly deserve (Figure 7.5). More than 1400 Earths could fit inside Jupiter, for example. These planets do not have solid surfaces on which future explorers might land. They are more like vast, spherical oceans with much smaller, dense cores. Figure 7.5. The ... |
(like a planet) is calculated using the equation An AU (or astronomical unit) is the distance from Earth to the Sun. 2 3 We give densities in units where the density of water is 1 g/cm3. To get densities in units of kg/m3, multiply the given value by 1000. 240 Chapter 7 Other Worlds: An Introduction to the Solar Syste... |
/l/30NASAmisspluto) and see high-resolution images of Pluto’s moon Charon. Smaller Members of the Solar System Most of the planets are accompanied by one or more moons; only Mercury and Venus move through space alone. There are more than 180 known moons orbiting planets and dwarf planets (see Appendix G for a listing T... |
for a year before landing gently on its surface. (credit: modification of work by NASA/JHUAPL) Another class of small bodies is composed mostly of ice, made of frozen gases such as water, carbon dioxide, and carbon monoxide; these objects are called comets (see Figure 7.9). Comets also are remnants from the formation ... |
An Introduction to the Solar System 243 Figure 7.10. Carl Sagan (1934–1996) and Neil deGrasse Tyson. Sagan was Tyson’s inspiration to become a scientist. (credit “Sagan”: modification of work by NASA, JPL; credit “Tyson”: modification of work by Bruce F. Press) In the early 1960s, when many scientists still thought Ve... |
the television medium. His 13-part public television series, Cosmos, was seen by an estimated 500 million people in 60 countries and has become one of the most-watched series in the 244 Chapter 7 Other Worlds: An Introduction to the Solar System history of public broadcasting. A few astronomers scoffed at a scientist ... |
more than a foot away. The Earth-Moon system fits into a standard backpack. In this model, the Sun is nearly 1.5 meters in diameter, about the average height of an adult, and our Earth is at a distance of 150 meters—about one city block—from the Sun. Jupiter is five blocks away from the Sun, and its diameter is 15 cen... |
the moons of Uranus, which have names drawn from English literature). When William Herschel, a German immigrant to England, first discovered the planet we now call Uranus, he wanted to name it Georgium Sidus (George’s star) after King George III of his adopted country. This caused such an outcry among astronomers in o... |
controversial because we have discovered many other planetary systems that don’t look very much like our own. Even within our solar system, the planets differ greatly in size and chemical properties. The biggest dispute concerns Pluto, which is much smaller than the other eight major planets. The category of dwarf pla... |
the Cassini spacecraft in 2000. (credit: modification of work by NASA/JPL/ University of Arizona) Uranus and Neptune are much smaller than Jupiter and Saturn, but each also has a core of rock, metal, and ice. Uranus and Neptune were less efficient at attracting hydrogen and helium gas, so they have much smaller atmosp... |
Worlds: An Introduction to the Solar System Moons, Asteroids, and Comets Chemically and structurally, Earth’s Moon is like the terrestrial planets, but most moons are in the outer solar system, and they have compositions similar to the cores of the giant planets around which they orbit. The three largest moons—Ganymed... |
�s temperature is less than that of Mercury by the square root of 100, or a factor of 10: from 500 K to 50 K. In addition to its distance from the Sun, the surface temperature of a planet can be influenced strongly by its atmosphere. Without our atmospheric insulation (the greenhouse effect, which keeps the heat in), t... |
where life as we know it could survive. Recent human activity may be reducing the habitability of our planet by adding pollutants to the atmosphere, especially the potent greenhouse gas carbon dioxide. Human civilization is changing our planet dramatically, and these changes are not necessarily for the better. In a so... |
a bit of an “Earth-chauvinist” term, but it is so widely used that we bow to tradition.) Among the terrestrial planets, Earth and Venus have experienced the most geological activity over their histories, although some of the moons in the outer solar system are also surprisingly active. In contrast, our own Moon is a d... |
vast outpourings of molten rock or the erosive effects of water and ice, which we call planet weathering, have erased evidence of earlier epochs and present us with only a relatively young surface for investigation. Counting the Craters One way to estimate the age of a surface is by counting the number of impact crate... |
geological chronology for the Moon. Furthermore, a few samples of material from the Moon, Mars, and the large asteroid Vesta have fallen to Earth as meteorites and can be examined directly (see the chapter on Cosmic Samples and the Origin of the Solar System). Scientists measure the age of rocks using the properties o... |
shown here for conceptual purposes only. If you had 1 gram of pure radioactive nuclei with a half-life of 100 years, then after 100 years you would have 1/2 gram; after 200 years, 1/4 gram; after 300 years, only 1/8 gram; and so forth. However, the material does not disappear. Instead, the radioactive atoms are replac... |
. For the Moon’s surface to be so young would imply active geology on our satellite. Only in 1969, when the first Apollo samples were dated, did we learn that the Moon is an ancient, geologically dead world. Using such dating techniques, we have been able to determine the ages of both Earth and the Moon: each was forme... |
the Solar System 255 these exoplanet systems. But for now, let us focus on theories of how our own particular system has formed and evolved. Looking for Patterns One way to approach our question of origin is to look for regularities among the planets. We found, for example, that all the planets lie in nearly the same ... |
system is to look outward for evidence that other systems of planets are forming elsewhere. We cannot look back in time to the formation of our own system, but many stars in space are much younger than the Sun. In these systems, the processes of planet formation might still be accessible to direct observation. We obse... |
the planets Uranus and Pluto spin on their sides? Why does Venus spin slowly and in the opposite direction from the other planets? Why does the composition of the Moon resemble Earth in many ways and yet exhibit substantial differences? The answers to such questions probably lie in enormous collisions that took place ... |
see today; the comets and some asteroids may be leftover planetesimals radioactivity process by which certain kinds of atomic nuclei decay naturally, with the spontaneous emission of subatomic particles and gamma rays solar nebula the cloud of gas and dust from which the solar system formed terrestrial planet any of t... |
-life of a radioactive element is the time it takes for half the sample to decay; we determine how many half-lives have passed by how much of a sample remains the radioactive element and how much has become the decay product. In this way, we have estimated the age of the Moon and Earth to be roughly 4.5 billion years. ... |
� Sky & Telescope. (January 1999): 36. Good overview. 260 Websites Chapter 7 Other Worlds: An Introduction to the Solar System Gazetteer of Planetary Nomenclature: http://planetarynames.wr.usgs.gov/. Outlines the rules for naming bodies and features in the solar system. Planetary Photojournal: http://photojournal.jpl.n... |
Tyson (13:02). To Scale: The Solar System: https://www.youtube.com/watch?t=84&v=zR3Igc3Rhfg. Constructing a scale model of the solar system in the Nevada desert (7:06). COLLABORATIVE GROUP ACTIVITIES A. Discuss and make a list of the reasons why we humans might want to explore the other worlds in the solar system. Doe... |
.) G. In the Carl Sagan: Solar System Advocate feature, you learned that science fiction helped spark and sustain his interest in astronomy. Did any of the members of your group get interested in astronomy as a result of a science fiction story, movie, or TV show? Did any of the stories or films you or your group membe... |
on the Moon’s surface? 10. If Earth was to be hit by an extraterrestrial object, where in the solar system could it come from and how would we know its source region? 11. List some reasons that the study of the planets has progressed more in the past few decades than any other branch of astronomy. 12. Imagine you are ... |
block from the Sun. If you were to make a model of the distances in the solar system to match your height, with the Sun at the top of your head and Pluto at your feet, which planet would be near your waist? How far down would the zone of the terrestrial planets reach? 23. Seasons are a result of the inclination of a p... |
? (Hint: Use the values in your table to help explain your categorization.) Figuring For Yourself 31. Calculate the density of Jupiter. Show your work. Is it more or less dense than Earth? Why? 264 Chapter 7 Other Worlds: An Introduction to the Solar System 32. Calculate the density of Saturn. Show your work. How does ... |
about the history of our planet? As our first step in exploring the solar system in more detail, we turn to the most familiar planet, our own Earth. The first humans to see Earth as a blue sphere floating in the blackness of space were the astronauts who made the first voyage around the Moon in 1968. For many people, ... |
s 23 h 56 m 4 s 5.1 × 108 km2 5.514 g/cm3 1.00 bar Some Properties of Earth Escape velocity Rotational period Surface area Density Atmospheric pressure Table 8.1 Earth’s Interior The interior of a planet—even our own Earth—is difficult to study, and its composition and structure must be determined indirectly. Our only ... |
% of Earth’s surface and lies mostly submerged under the oceans. It is typically about 6 kilometers thick and is composed of volcanic rocks called basalt. Produced by the cooling of volcanic lava, basalts are made primarily of the elements silicon, oxygen, iron, aluminum, and magnesium. The continental crust covers 45%... |
a very high density. The separation of Earth into layers of different densities is an example of differentiation, the process of sorting the major components of a planet by density. The fact that Earth is differentiated suggests that it was once warm enough for its interior to melt, permitting the heavier metals to si... |
the first US Earth satellite, Explorer 1, which recorded the ions (charged particles) trapped in its inner part. The regions of high-energy ions in the magnetosphere are often called the Van Allen belts in recognition of the University of Iowa professor who built the scientific instrumentation for Explorer 1. Since 19... |
when high temperature or pressure alters igneous or sedimentary rock physically or chemically (the word metamorphic means “changed in form”). Metamorphic rocks are produced on Earth because geological activity carries surface rocks down to considerable depths and then brings them back up to the surface. Without such a... |
mechanisms may differ from that on Earth as a result of chemical makeup and other constraints. Earth’s crust and upper mantle (to a depth of about 60 kilometers) are divided into about a dozen tectonic plates that fit together like the pieces of a jigsaw puzzle (Figure 8.7). In some places, such as the Atlantic Ocean,... |
the twentieth century could such a proposal be more than speculation. The scientist who made the case for continental drift in 1920 was a German meteorologist and astronomer named Alfred Wegener (Figure 8.8). This OpenStax book is available for free at http://cnx.org/content/col11992/1.8 Chapter 8 Earth as a Planet 27... |
especially for him at the University of Graz (where he was, however, ostracized by most of the geology faculty). Four years later, on his fourth expedition to his beloved Greenland, he celebrated his fiftieth birthday with colleagues and then set off on foot toward a different camp on the island. He never made it; he ... |
kilometers, enough to renew the entire oceanic crust in a little more than 100 million years. This is a very short interval in geological time—less than 3% of the age of Earth. The present ocean basins thus turn out to be among the youngest features on our planet. As new crust is added to Earth, the old crust must go ... |
al plate is sliding sideways with respect to the other. The fault is marked by the valley running up the right side of the photo. Major slippages along this fault can produce extremely destructive earthquakes. (credit: John Wiley) Unfortunately for us, the motion along fault zones does not take place smoothly. The cree... |
accumulated strain, how much slippage will occur? Answer: The difference in time from 1857 to 2047 is 190 y, or 1.9 centuries. Because only half the strain is released, this is equivalent to half the annual rate of motion. The total slippage comes to 0.5 × 5 m/century × 1.9 centuries = 4.75 m. When two continental mas... |
at least 100 million years. As Earth’s plates have moved during that time, the hot spot has generated a 3500-kilometer-long chain of volcanic islands. The tallest Hawaiian volcanoes are among the largest individual mountains on Earth, more than 100 kilometers in diameter and rising 9 kilometers above the ocean floor. ... |
and airplanes fly. Within this region—called the troposphere—warm air, heated by the surface, rises and is replaced by descending currents of cooler air; this is an example of convection. This circulation generates clouds and wind. Within This OpenStax book is available for free at http://cnx.org/content/col11992/1.8 ... |
At these elevations, individual atoms can occasionally escape completely from the gravitational field of Earth. There is a continuous, slow leaking of atmosphere—especially of lightweight atoms, which move faster than heavy ones. Earth’s atmosphere cannot, for example, hold on for long to hydrogen or helium, which 280... |
a warm Earth would be dominated by water vapor and carbon dioxide, with a surface pressure nearing 400 bars. Several lines of evidence show that the composition of Earth’s atmosphere has changed over our planet’s history. Scientists can infer the amount of atmospheric oxygen, for example, by studying the chemistry of ... |
and centuries. Changes in climate (as opposed to the random variations in weather from one year to the next) are often difficult to detect over short time periods, but as they accumulate, their effect can be devastating. One saying is that “Climate is what you expect, and weather is what you get.” Modern farming is es... |
Chapter 8 Earth as a Planet 283 8.4 LIFE, CHEMICAL EVOLUTION, AND CLIMATE CHANGE Learning Objectives By the end of this section, you will be able to: Outline the origins and subsequent diversity of life on Earth Explain the ways that life and geological activity have influenced the evolution of the atmosphere Describe... |
, and other chemical building blocks of life. Therefore, it seems likely that these chemical building blocks were available very early in Earth’s history and they would have combined to make living organisms. 284 Chapter 8 Earth as a Planet For tens of millions of years after Earth’s formation, life (perhaps little mor... |
content/col11992/1.8 Chapter 8 Earth as a Planet 285 Figure 8.16. Tree of Life. This chart shows the main subdivisions of life on Earth and how they are related. Note that the animal and plant kingdoms are just short branches on the far right, along with the fungi. The most fundamental division of Earth’s living things... |
. Before that, it was unthinkable for life to venture outside the protective oceans, so the landmasses of Earth were barren. The presence of oxygen, and hence ozone, thus allowed colonization of the land. It also made possible a tremendous proliferation of animals, which lived by taking in and using the organic materia... |
or heat radiation, which is trapped by greenhouse gases such as water vapor, methane, and CO2 in the atmosphere. The result is a higher surface temperature for our planet. This OpenStax book is available for free at http://cnx.org/content/col11992/1.8 Chapter 8 Earth as a Planet 287 The greenhouse effect in a planetar... |
isotopic signatures of this added CO2 demonstrate that it is mostly coming from burning fossil fuels. (credit: modification of work by NOAA This short PBS video (https://openstax.org/l/30pbsgreengas) explains the physics of the greenhouse effect. 288 Chapter 8 Earth as a Planet Already climate change is widely apparen... |
result of rapid climate change. In recognition of our impact on the environment, scientists have proposed giving a new name to the current epoch, the anthropocine, when human activity started to have a significant global impact. Although not an officially approved name, the concept of “anthropocine” is useful for reco... |
, over the history of Earth, these impacts have had an important influence on the evolution of life. Figure 8.19. Ouarkziz Impact Crater. Located in Algeria, this crater (the round feature in the center) is the result of a meteor impact during the Cretaceous period. Although the crater has experienced heavy erosion, th... |
exploded over New York City in 1908; history books might today record it as one of the most deadly events in human history. Tens of thousands of people witnessed directly the explosion of a smaller (20-meter) projectile over the Russian city of Chelyabinsk on an early winter morning in 2013. It exploded at a height of... |
rarer) impacts, however, can disturb the ecological balance of the entire planet and thus influence the course of evolution. The best-documented large impact took place 65 million years ago, at the end of what is now called the Cretaceous period of geological history. This time in the history of life on Earth was mark... |
work by “Carport”/Wikimedia) Such a quantity of airborne material would have blocked sunlight completely, plunging Earth into a period of cold and darkness that lasted several months. Many plants dependent on sunlight would have died, leaving plant-eating animals without a food supply. Other worldwide effects included... |
of them were probably violent enough to strip the planet of most its atmosphere and to boil away its oceans. Such events would sterilize the planet, destroying any life that had begun. Life may have formed and been wiped out several times before our own microbial ancestors took hold sometime about 4 billion years ago.... |
surveys are one of the few really life-and-death projects carried out by astronomers, with a potential to help to save our planet from future major impacts The Torino Impact Hazard Scale (https://openstax.org/l/30torhazscale) is a method for categorizing the impact hazard associated with near-Earth objects such as ast... |
largest part of Earth’s interior; lies between the crust and the core mass extinction the sudden disappearance in the fossil record of a large number of species of life, to be replaced by fossils of new species in subsequent layers; mass extinctions are indicators of catastrophic changes in the environment, such as mi... |
crustal plates move slowly in response to mantle convection. The surface expression of plate tectonics includes continental drift, recycling of the ocean floor, mountain building, rift zones, subduction zones, faults, earthquakes, and volcanic eruptions of lava from the interior. 8.3 Earth’s Atmosphere The atmosphere ... |
tell us about the source and reversals of Earth’s magnetic field. Gurnis, M. “Sculpting the Earth from Inside Out.” Scientific American (March 2001): 40. On motions that lift and lower the continents. Hartmann, W. “Piecing Together Earth’s Early History.” Astronomy (June 1989): 24. Jewitt, D., & Young, E. “Oceans from... |
views.com/eng/earth.htm. Overview of Earth. 298 Impacts Chapter 8 Earth as a Planet B612 Foundation : https://b612foundation.org/. Set up by several astronauts for research and education about the asteroid threat to Earth and to build a telescope in space to search for dangerous asteroids. Lunar and Planetary Institute... |
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