12 Chapter Instructor's Manual
Answers to Review Questions
1. The metallic core of Earth is important to humans today because it supports our magnetic field, which prevents cosmic rays (solar winds) from reaching the surface. 2. Hydrogen and helium most likely made up much of the early universe. 3. Supernova. 4. The theory for the origin of the solar system, called the nebular hypothesis, states that approximately 5 billion years ago the bodies of the solar system condensed from an enormous cloud. As the cloud contracted and began to rotate, the protosun began forming. The protoplanets (planets in the making) formed from material that had condensed and accreted inside the cloud. The inner planets, Mercury, Venus, Earth, and Mars were unable to retain appreciable amounts of the lighter components of the primordial cloud while the outer planets (Jupiter, Saturn, Uranus, and Neptune) accumulated large amounts of hydrogen and other light materials because of their much colder temperatures. 5. Outgassing refers to the process by which Earth's early atmosphere was formed by gases, trapped in the planet's interior, erupted from volcanoes over millions of years. Outgassing continues today from hundreds of active volcanoes worldwide. 6. Earth's early atmosphere was composed mainly of water vapor and carbon dioxide. 7. The free oxygen in Earth's atmosphere today originated from green plants releasing oxygen during the process of photosynthesis. 8. Water in the first oceans came from the water vapor erupted from volcanoes via outgassing. 9. Carbon dioxide is highly soluble in water and it is removed from our atmosphere by the precipitation of calcium carbonate to form the chemical sedimentary rock, limestone. Marine organisms, such as foraminifera, remove calcium carbonate from seawater to make their shells and other hard parts. 10. Precambrian history is more difficult to decipher because of the lack of fossils, which hinders correlation of rocks. Also, rocks of this great age are metamorphosed and deformed, extensively eroded, and obscured by younger overlying strata. 11. Cratons are thoughts to form from the collision and accretion of various types of terranes. Such collisional tectonics deforms and metamorphoses the sediments caught between the converging crustal fragments, which shortens and thickens the developing crust. Partial melting in the deepest regions of these collision zones generates silica-rich magmas that intrude the crustal rocks above. 12. Supercontinents are large landmasses that contain all, or nearly all, of the existing continents on Earth at any given time. The supercontinent cycle is the idea that rifting and dispersal of one supercontinent is followed by a long period during which the fragments are gradually reassembled into a new supercontinent having a different configuration. 13. The movement of continents can produce global climate change because they change the patterns of ocean currents and global wind patterns. As a result of such changes, the distribution of temperatures and precipitation worldwide changed as well.
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Earth's Evolution through Geologic Time
14. (a) Paleozoic; (b) Precambrian; (c) Cenozoic; (d) Precambrian; (e) Mesozoic; (f) Cenozoic; (g) (h) Paleozoic; Paleozoic; (i) Mesozoic; (j) Precambrian; (k) Mesozoic; (l) Paleozoic; (m) Paleozoic; (n) Cenozoic; (o) Paleozoic; (p) Mesozoic; (q) Precambrian; (r) Cenozoic 15. During the Cenozoic the eastern continental margin of North America was tectonically stable and the site of abundant marine sedimentation. The western margin, on the other hand, was the leading edge of the North American plate. As a result, plate interactions during the Cenozoic gave rise to many events of mountain building, volcanism, and earthquakes in the West. 16. In order to move onto the land from the oceans plants had to develop a mechanism for obtaining water and also a structure that allowed them to stay upright, despite gravity and wind. 17. The lobe-finned fish are thought to have developed the ability to stay out of water for longer periods of time and eventually became the first amphibians. 18. Amphibians are not considered to be true land animals because they are born in the water and originally they have gills and tails. Over time these features disappear as the amphibians become air-breathing organisms with legs. 19. Unlike amphibians, reptiles have shell-covered eggs that can be laid on land. The appearance of shellcovered eggs in the Mesozoic eliminated a water-dwelling stage and it was an important evolutionary step in the development of reptiles. 20. The extinction of the dinosaurs is thought to have been caused by a large meteorite impacting Earth. This hypothesis is supported by a thin layer of sediment that contains high levels of iridium, an element rare in Earth's crust but found in high proportions in stony meteorites.
Answers to Earth System Questions
1. Earth's original atmosphere was made up of the gases water vapor, carbon dioxide, nitrogen, and several trace gases that were released by outgassing from molten rock from the interior (solid Earth). Eventually, carbon dioxide became mixed in the primitive oceans (hydrosphere) as they formed on the cooling surface. Plants (biosphere), through the process of photosynthesis, began releasing oxygen. Once the available iron wa...