Where did Earth's water come from? Scientists say it wasn't melted meteorites

Water makes up about 71 per cent of the Earth's surface, but how it came to the planet continues to stump scientists after a new study ruled the leading possibility out.

Scientists are nevertheless one step closer to understanding how water ended up on Earth, according to a study published in the journal “Nature” on March 15.

Previous studies suggested melted meteorites "floating around" in space since the formation of the solar system four and a half billion years ago could be a reason.

But new research says these meteorites had an "extremely low water content". In fact, they were one of driest extraterrestrial materials ever measured, the study says.

"These results, which let researchers rule them out as the primary source of Earth’s water, could have important implications for the search for water—and life—on other planets," the study reads.

A team of researchers led by the University of Maryland, analyzed seven melted, stony meteorites that crashed into Earth billions of years ago. The team was able to pull fragments that showed these meteorites were pieces of planetesimals, which are objects that collided to form the planets in our solar system.

When planetesimals were heated up by radioactive elements in the early history of the solar system, more pieces separated.

Researchers said the meteorites that were tested fell to Earth recently, making the new study "the first time anyone had ever measured their water contents."

Earth’s water did not come from melted meteorites, according to a new study that analyzed melted meteorites that had been floating around in space since the solar system’s formation four and a half billion years ago. (Illustration by Jack Cook, ©Woods Hole Oceanographic Institution)

Scientists left some samples under a high-powered vacuum for over a month in order to suck out enough water to be tested.

When the testing was complete, the meteorites failed to offer the solution of where Earth's water originated.

"We knew that plenty of outer solar system objects were differentiated, but it was sort of implicitly assumed that because they were from the outer solar system they must also contain a lot of water," Sune Nielsen, associate scientist, Geology & Geophysics at the Woods Hole Oceanographic Institution, said in a press release. "Our paper shows this is definitely not the case. As soon as meteorites melt, there is essentially no remaining water."

Some of the samples used were from the inner solar system (where Earth is located) and other "rarer" samples came from the colder, icier outer regions of the solar system.

"While it was generally thought that water came to Earth from the outer solar system, it has yet to be determined what types of objects could have carried that water across the solar system," the study says.