An analysis of meteorites from the inner solar system hints that water may have arrived along with the rocks that formed Earth.
According to some models of planet formation, early Earth should have been completely dry, because the young sun was too hot to allow much ice or liquid water to stick to the rocks that eventually formed Earth and the other inner planets.
There is a type of modern meteorite – called an enstatite chondrite – that is similar to those pre-Earth rocks. Because these meteorites were thought to be dry, many researchers thought that Earth’s water was delivered well after its formation by wetter meteorites born further from the sun.
Laurette Piani at the University of Lorraine in France and her colleagues analysed 13 enstatite chondrites and measured their hydrogen content as a proxy for water. They found that the rocks were far wetter than expected, with the equivalent of 0.08 to 0.54 per cent water by weight.
“These meteorites are one of the best analogues we have for Earth’s building blocks, and they are not as dry as we though,” says Piani. “This water was probably in the building blocks over the whole formation process of Earth.”
If Earth was built from enstatite chondrites, they could have provided about three times as much water as fills the planet’s oceans now. “If this material provided water to the Earth, it could have also been present in the building blocks of Mercury, Venus and Mars,” says Piani. The planets of the inner solar system could have been wet from the very beginning.