New Evidence May Show Where Earth’s Water Came From

A study published this week offers evidence regarding how water originated on Earth, and the clues come from some of the oldest rocks in the solar system. Earth’s abundance of water makes it unique in the solar system, but scientists have never been sure how it got here. Some believed the water – or chemical compounds that make up water – was here all along, embedded in the original rock that formed the Earth about 4.5 billion years ago.  A piece of an enstatite chondrite meteorite, which contains about 0.5 weight percent of water, is seen in this undated handout obtained Aug. 27, 2020, courtesy of Laurette Piani and Christine Fieni from the Museum of Natural History in Paris.But other scientists studying models of where Earth exists in the solar system think it should have formed as a dry planet, suggesting the water came from somewhere else. A study, published Thursday in the journal Science, looks at the composition of samples of enstatite chondrite meteorites — a rare, ancient form of meteorite believed to have been formed very early in the life of the solar system.Scientists had previously dismissed these space rocks as the source of Earth’s water because they were exposed to the heat and radiation of the young sun early in their formation, making them, the scientists thought, too dry to carry water. Instead, astronomers theorize water came to Earth later in its formation, through carbonaceous chondrite meteorites, which came from the outer solar system, where water was more abundant. In the new study, researchers measured the amount of hydrogen, the primary element in water, in 13 samples of enstatite chondrite meteorites. Their analysis revealed these meteorites carry a lot more hydrogen than previously believed. So much hydrogen, that the study’s authors say they believe the ancient meteorites can account for least three times the amount of water in Earth’s present-day oceans. Therefore, they maintain, Earth’s water may have come from the very space rocks that formed the planet. 
 


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