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Are comets the origin of Earth’s oceans?

From The Daily Beast:

Water, water everywhere, but where did it come from? One common explanation is that the water in Earth’s oceans was brought by comets, which bombarded the planet during its earliest period. It’s a simple, logical, and testable story.

But that doesn’t mean it’s right. A new study published last week in Science revealed that the water on Comet 67P/Churyumov-Gerasimenko doesn’t match that found on Earth. Specifically, instruments aboard the Rosetta probe measured the relative amount of deuterium in the comet’s water and found it was roughly three times higher than the amount in Earth’s oceans. Comets are chemically pristine, mostly unchanged over the Solar System’s 4.5 billion year history, so a mismatch in the deuterium content complicates the story of Earth’s water. [Read more at The Daily Beast….]