Some of the oldest known meteorites can simply explain how water came to Earth. Gizmodo scientists are reported to have found evidence that carbon chondrites, a group of meteorites from the formation of the solar system (about 4.5 billion years ago), held liquid water until “only” a few hundred thousand years ago. Then they may have flooded the Earth with water when it was still very young.
The researchers dated the water flow in the rocks using a uranium-thorium combination. Because uranium is highly mobile in liquid, while thorium is relatively static, scientists could tell when water last flowed through meteorites. As this signature disappears over time, its presence makes it clear that the water has been active relatively recently.