Text 1 The origin of Earth's water remains a debate. A popular hypothesis suggests that water was delivered by icy comets during the "Late Heavy Bombardment" period, roughly 4 billion years ago. Proponents of this view point to computer simulations of solar system evolution, which show that the gravitational pull of giant planets would have flung vast numbers of water-rich comets from the outer solar system directly toward Earth.
Text 2 Cosmochemist Dr. Lewis and his team argue that the "comet delivery" hypothesis is contradicted by chemical evidence. They analyzed the isotopic ratio of deuterium to hydrogen in comet water and found it is significantly heavier than the water found in Earth’s oceans. Conversely, water found in rocky asteroids from the inner solar system matches Earth’s isotopic signature perfectly. Lewis concludes that asteroids, not comets, were the primary source of Earth's oceans.
Based on the texts, how would Dr. Lewis (Text 2) most likely respond to the hypothesis supported by the computer simulations in Text 1?
By asserting that the simulations are incorrect because they fail to account for the gravitational pull of the moon
By arguing that while comets may have hit Earth, isotopic evidence suggests they were not the primary source of the planet's water
By suggesting that the water on Earth has changed its chemical composition over 4 billion years, making comparisons impossible
By agreeing that comets delivered the water but disputing the timing of the Late Heavy Bombardment
Correct Answer: B
Choice B is the best answer. Text 1 relies on computer simulations to suggest comets brought water. Text 2 relies on chemical evidence (isotopic ratios) to show that comet water doesn't match Earth water, while asteroid water does. Thus, Lewis would argue that despite the simulations, the hard chemical evidence suggests comets were not the primary source.
Choice A is incorrect because Text 2 does not mention the moon. Choice C is incorrect because Text 2 relies on the comparison being valid to make its point about asteroids. Choice D is incorrect because Text 2 disagrees with the source (comets), not necessarily the timing.