Scientists from the Woods Hole Oceanographic Institution in Massachusetts found in a study that the water on Earth arrived earlier than previously thought.

"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," said Adam Sarafian, the lead author of the paper and a MIT/WHOI Joint Program student in the Geology and Geophysics Department.

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One school of thought was that planets were formed without moisture, because of the high-impact, high-energy process of the birth of planets, and that the water would arrive later from sources such as "wet" asteroids, which were mostly comprised of gases and ice, or comets.

"With giant asteroids and meteors colliding, there's a lot of destruction," said Horst Marschall, a geologist at WHOI and coauthor of the paper. "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 much, much later --hundreds of millions of years later."

The researchers turned carbonaceous chondrites, the most ancient known meteorites, as another possible source for the water on Earth.  The carbonaceous chondrites, which were formed in the same swirl of grit, ice, gases and dust that produced the Sun approximately 4.6 billion years ago, came into existence well before the earliest planets were born.

Sune Nielsen, coauthor of the paper and WHOI geologist, said that the primitive meteorites resemble the majority of the composition of the solar system.

"They have quite a lot of water in them, and have been thought of before as candidates for the origin of Earth's water."

To be able to learn the origin of the water in planetary bodies, researchers measure the ratio between hydrogen's two stable isotopes: hydrogen and deuterium. Various areas of the solar system are attributed with highly different ratios of the isotopes. With the knowledge of the ratio of carbonaceous chondrites, the study's authors reasoned that if they are able to compare it to an object that was known to crystallize during the time that Earth was still being formed, they could estimate when water sprung up on Earth.

The scientists tested the hypothesis, using meteorite samples given by NASA from the 4-Vesta asteroid, which was born in the same area of the solar system as Earth. The surface of 4-Vesta is composed of frozen lava, or basaltic rock, and the meteorites of the material known as eucrites carry a special signature of the oldest hydrogen pools in the solar system.

The ratio of the isotopes on the asteroid are identical to that of the composition of the carbonaceous chondrites, which is similar to that of Earth. The finding, combined with the isotope data of nitrogen, suggest that the carbonaceous chondrites are most likely the source of water.

Tagswater, Origin of water, Earth, Ocean, solar system, Sun, Carbonaceous chondrite