Earth’s water has been present since the planet’s earliest days
Studies of meteorite samples known to have come from the protoplanet Vesta indicate Earth’s surface had water much earlier than scientists previously believed. Oceans, which now cover 70 percent of the planet, were here as early as 14 million years after the solar system formed.
The origin of Earth’s water has long been a mystery to scientists. Many theorized the water came from icy comets and asteroids. But a new study published in the journal Science, led by Adam Sarafian of the Woods Hole Oceanographic Institution and geologist Horst Marschall, debunks that view.
Water present as ice in icy comets and asteroids could not have survived their impact with early Earth and would have either evaporated or been blown back into space, Marschall said. A different theory is that Earth’s water came from carbonaceous chondrites, ancient meteorites that formed with the Sun when the solar system first formed 4.6 billion years ago, predating the planets.
Carbonaceous chondrites contain significant amounts of water, which they could have brought to early Earth. The recent study focused on the ratio of deuterium and hydrogen, the two stable isotopes of hydrogen. These are known to be present in meteorite samples that originated from Vesta, which NASA provided. Vesta itself has been shown to have the same hydrogen isotope composition as the meteorites.