### The Origin of Earth's Water
Scientists debate the origin of Earth’s water and volatile elements. Two main hypotheses have been proposed:
Hypothesis 1
Earth formed in a hot, dry region of the inner solar nebula, inside the "snow line," where water ice could not condense. Consequently, the proto-Earth was completely dry. Earth's water was delivered later during the "Late Veneer" phase, approximately 100 to 300 million years after formation, via impacts of water-rich carbonaceous chondrites and comets from the outer solar system.
Hypothesis 2
Earth's water is endogenous (originating in-situ). During accretion, hydrogen from the solar nebula gas adsorbed directly onto iron-rich silicate dust grains. As these grains clumped to form the early Earth, the hydrogen was trapped inside the mantle. Over time, internal heat and volcanic activity outgassed this water to the surface, forming the oceans.
Suppose researchers discover that primitive, undisturbed rocks from Baffin Island (representing Earth's early mantle before major geological mixing) contain water with a deuterium-to-hydrogen () ratio that is 25\% lower than the average ratio of carbonaceous chondrites, but closely matches the estimated ratio of the solar nebula gas. Which of the following statements best describes how this new evidence affects the two hypotheses?
- AIt supports Hypothesis 1 and weakens Hypothesis 2, because the low ratio matches the solar nebula gas and differs from that of carbonaceous chondrites.
- BIt weakens both Hypothesis 1 and Hypothesis 2, because Baffin Island rocks should show a mixture of both isotopic signatures to support either hypothesis.
- It supports Hypothesis 2 and weakens Hypothesis 1, because the low ratio matches the solar nebula gas and differs from that of carbonaceous chondrites.Answer
- DIt has no effect on either hypothesis, because Baffin Island rocks represent the mantle after core formation, which is unrelated to the source of water.