Explanation
Correct answer: A.
Choice A is the best answer because it most accurately describes what Stern and Gerya most likely believe about the development of complex life on exoplanets. The text indicates that the search for extraterrestrial life already focuses on atmosphere-bearing planets in the habitable zone because their conditions are best suited for complex organisms. Stern and Gerya claim that plate tectonics on Earth accelerated the emergence of complex organisms, and they therefore hold that tectonics could “help further narrow the search.” This phrase implies that plate tectonics should be added to the existing criteria. In other words, the text implies that among habitable zone planets with atmospheres, those that also have plate tectonics would be more likely to enable the development of complex life than otherwise similar planets lacking plate tectonics.
Why the other choices are wrong
Choice B
Choice B is incorrect because the text doesn’t address whether the timing of the transition to plate tectonics—early versus late in a planet’s history—affects the likelihood of complex life. Although the text mentions that plate tectonics emerged on Earth after a “long transition” and that this process accelerated the development of complex life, it presents these details as context for why plate tectonics matter, not as a claim about when the transition would have needed to occur within the planet’s history.
Choice C
Choice C is incorrect because the text doesn’t discuss the timing of the acquisition of an atmosphere in relation to that of the transition to plate tectonics or explain why this would be relevant to the development of complex life. Rather, the text presents these as independent factors relevant to the search for extraterrestrial life.
Choice D
Choice D is incorrect because the text presents plate tectonics as an additional factor to consider alongside orbital distance from a host star and atmosphere, not as a more important one. Stern and Gerya propose that tectonics could “help further narrow the search,” which implies supplementing, rather than superseding, the existing criteria.