Earth is known as the Blue Planet because of its oceans, which cover more than 70 per cent of the planets surface and are home to the worlds greatest diversity of life.
While some hypothesise that water came late to Earth, well after the planet had formed, findings from a new study led by scientists at the Woods Hole Oceanographic Institution (WHOI) significantly move 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 didnt get them from a late process, as was previously thought, said Adam Sarafian, the lead author of the paper.
The studys authors turned to a potential source of Earths 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.
These primitive meteorites resemble the bulk solar system composition, said WHOI geologist and coauthor Sune Nielsen.
They have quite a lot of water in them, and have been thought of before as candidates for the origin of Earths water, Nielsen said.
In order to determine the source of water in planetary bodies, scientists measure the ratio between the two stable isotopes of hydrogen: deuterium and hydrogen.
The research team, which also includes Francis McCubbin from the Institute of Meteoritics at the University of New Mexico and Brian Monteleone of WHOI, utilised meteorite samples provided by NASA from the asteroid 4-Vesta.
The asteroid 4-Vesta, which formed in the same region of the solar system as Earth, has a surface of basaltic rock frozen lava.
These basaltic meteorites from 4-Vesta are known as eucrites and carry a unique signature of one of the oldest hydrogen reservoirs in the solar system.
Their age approximately 14 million years after the solar system formed makes them ideal for determining the source of water in the inner solar system at a time when Earth was in its main building phase.
The researchers analysed five different samples, the first time hydrogen isotopes have been measured in eucrite meteorites.
The measurements show that 4-Vesta contains the same hydrogen isotopic composition as carbonaceous chondrites, which is also that of Earth. That, combined with nitrogen isotope data, points to carbonaceous chondrites as the most likely common source of water.
The study shows that Earths water most likely accreted at the same time as the rock. The planet formed as a wet planet with water on the surface, Marschall said.
The study was published in the journal Science.