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Lecture II.4. Answers to the Questions.
1. (2 pts) Animals colonized the land during the Devonian period. This was during the _________ era and the
__________ eon.
Paleozoic; Phanerozoic
2. (2 pts) The mother of all mass extinctions occurred at the end of the _______ period and the ________ era.
Permian; Paleozoic.
3. (4 pts) The lack of Precambrian fossils reflects which of the following factors? (There may be more than one correct answer.) a. Lack of Precambrian organisms.
b. Lack of readily fossilized hard parts – shells, skeletons, teeth, etc.
c. Lack of fossil-bearing rock.
d. Lack of scientific interest in studying Precambrian strata. e. None of the above. There are lots of Precambrian fossils. b., c.
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4. (2 pts) Which two mass extinction events were coincident with massive volcanic eruptions that left enormous deposits of lava called traps?
Permo-Triassic (end-Permian) and Cretaceous-
Tertiary (end-Cretaceous).
5. (6 pts) You invent a time machine and travel back in time seven million years (early Miocene) to South America.
You observe large, cat-like creatures stalking a herd of hoofed mammals. Are the predators marsupials or placentals? Explain your answer. Hint. When did the
Panamanian land bridge form between North and South
America?
Marsupials. The Panamanian land bridge wouldn’t form for another 4 million years (Pliocene), at which time placental carnivores invaded South
America and indigenous marsupial predators went extinct.
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6. (2 pts) Why were stromatolites important in the evolution of the earth’s atmosphere?
Photosynthetic bacteria living in stromatolites oxygenated atmosphere.
7. (4 pts) Regarding the origin of life, why is it important whether the primitive atmosphere was reducing or mildly oxidizing? Amino acids and other building blocks of life are more readily produced in a reducing environment.
8. (6 pts) In 2011, NASA biologists announced the detection of adenine and guanine in carbonaceous chondrites
(meteorites with a high organic fraction). What evidence did the scientists give to support their claim that these nucleobases are truly of extraterrestrial origin, i.e., as opposed to having resulted from contamination?
1. The meteorites contained nucleobase-related compounds not found in terrestrial organisms.
2. The concentration of the nucleobases in the surrounding ice and soil was on the order of thousand times less than in the meteorites themselves. 4
3. The nucleobases (biological and nonbiological) detected in the meteorites can be synthesized abiotically by reacting hydrogen cyanide, ammonia and water.
9. (8 pts) Why could the removal of methane from the earth’s atmosphere by accumulating concentrations of molecular oxygen have caused the climate to cool?
Methane removal increased the rate at which energy from the sun was radiated back into space as heat. In greater detail: Earth’s temperature is determined by a balance between incoming and outgoing energy, the former as shortwave radiation; the latter re-radiated as heat (long wave radiation).
Greenhouse gases such as methane, water and carbon dioxide, retard re-radiation and thus warm the earth and its atmosphere. As noted in lecture, oxygen reacts with methane to yield water and carbon