ALBUQUERQUE, N.M. — That water you use to make your morning coffee appears to have been on Earth for a very long time – longer than previously believed, new research suggests.
The research, by a team based in part at the University of New Mexico’s Institute of Meteoritics, tackles a mystery about one of our most ordinary yet essential substances. “Earth has all this water,” said UNM researcher Francis McCubbin, co-author of a paper published today “but no one knows where it came from.”
The most common scientific explanation was that Earth formed as a dry planet, which later got a delivery of life-giving water via a bombardment of icy comets. But the research team, led by Woods Hole Oceanographic Institution graduate student Adam Sarafian and including McCubbin, thinks it has found evidence that the water was here from very near the beginning.
Water in rocks left over from the earliest formation of Earth’s solar system neighborhood, studied at UNM and Woods Hole in Massachusetts, bears the same chemical fingerprint as the water that dominates Earth’s surface today, according to the new research.
Our solar system formed more than 4 billion years ago when a cloud of dust and gas coalesced, with a star – our sun – in the center. Smaller bits clumped together under the growing tug of their own gravitational attraction to form the orbiting planets.
Scientists had long suspected that the inner part of the solar system, nearer to the sun, was too hot for water during this early part of formation – like the lower slopes of a mountain where it is too warm for snow to stick. “The idea that a lot of people had was that there’s this thing called the ‘snow line,'” McCubbin said.
Under that theory, the inner solar system was dry. Water lurked in the outer reaches of the solar system, locked up in icy comets. Only later, once Earth had finished forming, that theory went, was the water added through cometary bombardment.
The new work by Sarafian, McCubbin and their colleagues could upend that theory.
They studied water trapped in minerals in some of the inner solar system’s earliest meteorites, some of them in the permanent research collection of UNM’s Institute of Meteoritics. Far from being dry, the scientists realized, the region of the solar system where Earth formed had water from the beginning.
“Water was mixing all through the inner solar system,” McCubbin said. As Earth was coalescing from the initial rocky debris of the early solar system, rocks with water in them were being added the whole time, the scientists argue.
That is consistent with earlier research by McCubbin on meteorites from Mars, one of the rocky planets that also formed in the inner part of the solar system not far – in solar system terms – from Earth.
But perhaps more important, the scientists used a technique called “isotopic analysis” to conclude that the composition of the atoms in the water molecules matched the water currently found all around us here on Earth.
That does not mean that comets did not add to Earth’s water supply later, according to the scientists. But by matching the water on Earth to the water in the meteorites, they say they have demonstrated that much of the water now on our planet likely has been here since the earliest days of Earth’s formation.