1. 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.
2. Free oxygen in Earth's atmosphere originated from the
oxygen released by
green plants during the process of photosynthesis.
3. (a) late Paleozoic; (b) Precambrian; (c) Cenozoic; (d)
Precambrian; (e) Mesozoic; (f) late Paleozoic; (g) Cenozoic; (h) early
Paleozoic; (i) Mesozoic; (j) late Paleozoic; (k)
Cenozoic; (l) Precambrian; (m) Mesozoic; (n) late Paleozoic; (o) early
Paleozoic; (p) Mesozoic; (q) Cenozoic; (r) early Paleozoic; (s) Mesozoic; (t)
Cenozoic; (u) Precambrian; (v) early Paleozoic;
(w) Cenozoic
4. One proposal suggests that hard parts evolved for
survival; however, the fact that predators were not abundant until after hard
parts had evolved suggests other possible explanations. Perhaps the evolution
of hard parts occurred to give organisms the ability to grow larger or more
erect, or to allow their body organs to have a more controlled environment.
More than likely the evolution of hard parts was in response to a variety of
conditions.
5. Unlike amphibians, reptiles have shell-covered eggs
that can be laid on land. Furthermore, reptiles readily adapted to the drier
Mesozoic climates and were the first true terrestrial animals. Mammals are
distinct from reptiles because mammalian young are born live, and mammals
maintain a steady body temperature. Other mammalian adaptations included the
development of insulating body hair and a more efficient heart and lungs.
6. One hypothesis for the extinction of the dinosaurs is
that a large asteroid or comet collided with Earth, producing a dust cloud that
reduced the amount of sunlight that reached the surface. The collapse of food
chains and other associated environmental events caused mass extinction. Other
scientists disagree, claiming that what appears to be a mass extinction over a
short period of time actually occurred over a much broader time span, and the
decline of the dinosaurs was gradual.
7. During the Cenozoic the eastern continental margin of
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 was oxidized, substantial quantities of free
oxygen accumulated in the atmosphere.
One hypothesis for the extinction of the dinosaurs is
that about 65 million years ago a large meteorite collided with Earth. The huge
quantities of dust blasted into the atmosphere by the impact reduced the amount of
sunlight reaching Earth’s surface. Reduced sunlight and cooler temperatures
caused delicate food chains to collapse, eventually triggering the mass
extinction that marked the end of the dinosaurs.
2. Carboniferous coal swamps were
characterized by lush tropical-like vegetation such as large trees with scales,
seed ferns, and scouring rushes, as well as large insects. During this time,