JOIN USDebunking previous theories that water came late to Earth well after the planet had formed, researchers have significantly moved back the clock for the first evidence of water on Earth and in the inner solar system.
"The answer to one of the basic questions is that our oceans were always here. We did not get them from a late process as was previously thought," claimed lead scientist Adam Sarafian from the Woods Hole Oceanographic Institution (WHOI) in Massachusetts.
One school of thought is that planets originally formed dry due to the high-energy, high-impact process of planet formation.
Then the water came later from sources such as comets or "wet" asteroids which are largely composed of ices and gases. "With giant asteroids and meteors colliding, there is a lot of destruction," said Horst Marschall, a geologist at WHOI.
"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 and that surface water as it exists on our planet today must have come hundreds of millions of years later," he explained.
The team then turned to another potential source of Earth's water - carbonaceous chondrites.
The most primitive known meteorites, carbonaceous chondrites were formed in the same swirl of dust, grit, ice and gasses that gave rise to the sun some 4.6 billion years ago - well before the planets were formed.
To test this hypothesis, the team utilised meteorite samples provided by NASA from the asteroid 4-Vesta.
The asteroid 4-Vesta which was formed in the same region of the solar system as Earth has a surface of basaltic rock - frozen lava.
These 14-million year old basaltic meteorites are known to carry a unique signature of one of the oldest hydrogen reservoirs in the solar system.
"The study shows that Earth's water most likely accreted at the same time as the rock. The planet formed as a wet planet with water on the surface," noted WHOI geologist and co-author Sune Nielsen. The paper was published in the journal Science.