Water covers about 70 percent of our planet’s surface. Initially, scientists believed that Earth formed dry, with a molten surface created by the impacts of other objects from space. Collisions with asteroids and wet comets supposedly brought water to our planet much later. “Some people have argued that any water molecules that were present as the planets were forming would have evaporated or been blown off into space,” said geologist Horst Marschall. “[Scientists thought that] surface water as it exists on our planet today must have come much later—hundreds of millions of years later.”
But a new study shows that Earth had water on its surface when it formed, enough for life to have evolved earlier than originally believed. The same may be true for other planets in our inner solar system before their environments turned hostile.
To determine when water arrived on Earth, researchers compared two sets of meteorites. The first set, carbonaceous chondrites, are the most ancient meteorites ever identified. They came into existence about the same time as our sun, before any planets developed. The second set of meteorites are believed to have come from Vesta, a big asteroid that formed in the same general area as Earth about 14 million years after our solar system was born.The two types of meteorites share the same chemistry and contain a lot of water. For that reason, the researchers believe that Earth formed with water on its surface from the carbonaceous chondrites about 4.6 billion years ago.
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