Solar System Ice: Source Of Earth’s Water

Scientists have long believed that comets and a type of very primitive meteorite called carbonaceous chondrites were the sources of early Earth’s volatile elements — which include hydrogen, nitrogen, and carbon — and possibly organic material, too. Understanding where these volatiles came from is crucial for determining the origins of both water and life on the planet. New research led by Carnegie’s Conel Alexander focuses on frozen water that was distributed throughout much of the early solar system, but probably not in the materials that aggregated to initially form Earth.
The evidence for this ice is now preserved in objects like comets and water-bearing carbonaceous chondrites. The team’s findings contradict prevailing theories about the relationship between these two types of bodies and suggest that meteorites, and their parent asteroids, are the most-likely sources of the Earth’s water. Their work is published July 12 by Science Express.
Looking at the ratio of hydrogen to its heavy isotope deuterium in frozen water (H2O), scientists can get an idea of the relative distance from the Sun at which objects containing the water were formed. Objects that formed farther out should generally have higher deuterium content in their ice than objects that formed closer to the Sun, and objects that formed in the same regions should have similar hydrogen isotopic compositions. Therefore, by comparing the deuterium content of water in carbonaceous chondrites to the deuterium content of comets, it is possible to tell if they formed in similar reaches of the solar system.

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