The ocean, a massive expanse of water that today covers 70 percent of the planet, flooded ancient Earth earlier than thought, scientists reported Thursday - just 14 million years after the start of the solar system.
It seems as far back as we can tell, Earth was known as the Blue Planet. While we have always known that water is essential to all life, when and where our water came from has long eluded scientists, until now.
"The answer to one of the basic questions is that our oceans were always here. We didn't get them from a late process, as was previously thought," study lead author Adam Sarafian, with the Woods Hole Oceanographic Institution, said in a press release.
One initial theory was that an early "dry" Earth quenched its thirst for water after "wet" comets and asteroids, composed largely of ice and gases, brought it to the planet. However, according to geologist Horst Marschall, a co-author of the study, such collisions would have made it nearly impossible for water to survive, as it would have evaporated or been blown into space from the blast.
"Surface water as it exists on our planet today, must have come much, much later - hundreds of millions of years later," he explained.
Another theory came from carbonaceous chondrites, the most primitive kinds of meteorites, which formed from the same grit and grime that created the Sun some 4.6 billion years ago - well before the planets came into existence. And because they contained a lot of water, they were seen as potential candidates for the origin of early Earth's oceans.
So to get to the bottom of the mystery, researchers measured the ratio between the two stable isotopes of hydrogen: deuterium and hydrogen. These elements match what has been found in carbonaceous chrondrites, and so are good indicators of when water first appeared on Earth. They used meteorite samples provided by NASA from the asteroid 4-Vesta, which dates back to 14 million years after the start of the solar system.
Astonishingly, the results show that 4-Vesta contains the same hydrogen isotopic composition as carbonaceous chondrites, which is also that of Earth - meaning, these ancient, unaltered meteorites are most likely the source of Earth's water.
"All the planets could have gotten their water very early, which means the planets could have been habitable immediately after they formed. They weren't just sitting there and looking at their watch, waiting for water to come," Sarafian told Discovery News.
The scientists next plan to study an even rarer group of meteorites called angrites that date back to just two million years after the formation of the solar system. So even though this latest study shows that Earth was inundated with water earlier than previously thought, the age of our oceans could possibly be pushed back even further.
The research appears in the journal Science.