Exam 25: The History of Life on Earth

The following questions refer to the description and figure below. The figure represents a cross section of the sea floor through a mid-ocean rift valley, with alternating patches of black and white indicating sea floor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley), the igneous rock of the sea floor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about 1 million years old, and potassium-40 dating is typically used to date such rocks. NOTE: the dashed horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley. Figure 25.1 -Let's say that a hypothetical submersible robot was used to collect samples of sedimentary rock from the sea floor along the section illustrated. The robot moved back and forth along the transect, collecting first from site A, then site III, then site B, then site II, and lastly site D. Assuming that sedimentation has occurred at a constant rate along the transect over the past million years, rearrange the sites mentioned above on the basis of the thickness of the sediments overlying the igneous rock, from thickest to thinnest.

The following questions are based on the observation that several dozen different proteins comprise the prokaryotic flagellum and its attachment to the prokaryotic cell, producing a highly complex structure. -In certain motile prokaryotes, dozens of different proteins comprise the motor that powers the prokaryotic flagellum. The motor has a complicated structure, and its various proteins interact to carry out its function. Based on Darwin's explanation for the existence of human eyes, how would he probably have explained the existence of such motors?

The following questions refer to this hypothetical situation: A female fly, full of fertilized eggs, is swept by high winds to an island far out to sea. She is the first fly to arrive on this island, and the only fly to arrive in this way. Thousands of years later, her numerous offspring occupy the island, but none of them resembles her. There are, instead, several species each of which eats only a certain type of food. None of the species can fly, for their flight wings are absent, and their balancing organs (i.e., halteres) are now used in courtship displays. The male members of each species bear modified halteres that are unique in appearance to their species. Females bear vestigial halteres. The ranges of all of the daughter species overlap. -In each fly species, the entire body segment that gave rise to the original flight wings is missing. The mutation(s)that led to the flightless condition could have

The following questions refer to the description and figure below. The figure represents a cross section of the sea floor through a mid-ocean rift valley, with alternating patches of black and white indicating sea floor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley), the igneous rock of the sea floor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about 1 million years old, and potassium-40 dating is typically used to date such rocks. NOTE: the dashed horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley. Figure 25.1 -If it were possible to conduct sophisticated microscopic and chemical analyses of microfossils found in 3.2-billion-year-old stromatolites, then within such microfossils, one should be surprised to observe evidence of: I. double-stranded DNA II. a nuclear envelope III. a nucleoid IV. a nucleolus V. nucleic acids

The following questions refer to the description and figure below. The figure represents a cross section of the sea floor through a mid-ocean rift valley, with alternating patches of black and white indicating sea floor with reversed magnetic polarities. At the arrow labeled "I" (the rift valley), the igneous rock of the sea floor is so young that it can be accurately dated using carbon-14 dating. At the arrow labeled "III," however, the igneous rock is about 1 million years old, and potassium-40 dating is typically used to date such rocks. NOTE: the dashed horizontal arrows indicate the direction of sea-floor spreading, away from the rift valley. Figure 25.1 -A major evolutionary episode that corresponds in time most closely with the formation of Pangaea was the