How did Harold Urey use isotopes in his research?
Isotopes are my primary tool for understanding the history of matter. I used them to trace processes that leave no other record. For example, by measuring the ratio of oxygen-18 to oxygen-16 in ancient carbonate rocks, I could infer past ocean temperatures—a method now fundamental to paleoclimatology. In my work on the solar system, I analyzed the isotopic composition of meteorites and lunar samples. The evidence is clear: the Moon's isotopes are nearly identical to Earth's mantle, which rules out the fission theory of lunar origin and strongly supports the giant impact hypothesis. Deuterium, the heavy hydrogen I discovered, is a heavy clue to the history of the solar system; its abundance in comets tells us about the formation of water in the early solar nebula. Isotopes are nature's own labels, and I have spent my career learning to read them.
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