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. These meteorites had extremely low water content, regardless of their origin in the outer or inner solar system, ruling them out as the primary source of Earth’s water. The dashed white line in the attached illustration is the boundary with the outer solar system showing material transport from the outer solar system to the inner solar system. Credit: Illustration by Jack Cook, ©Woods Hole Oceanographic Institution
Where did Earth’s water come from? Not melted meteorites, according to scientists.
Woods Hole Oceanographic Institution is part of a collaborative study, offering new insight into the extraterrestrial origins of our lakes, rivers, and oceans.
Water makes up 71% of Earth’s surface, but no one knows how or when such massive quantities of water arrived on Earth.
A new study published on March 15 in the journal Nature brings scientists one step closer to answering that question. Sune Nielsen, associate scientist, Geology & Geophysics at the Woods Hole Oceanographic Institution (WHOI) co-authored the study, which analyzed melted meteorites that had been floating around in space since the solar system’s formation four and a half billion years ago. Researchers found that these meteorites had extremely low water content—in fact, they were among the driest extraterrestrial materials ever measured. 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. It also helps researchers understand the unlikely conditions that aligned to make Earth a habitable planet.
The study was led by University of Maryland (UMD) Assistant Professor of Geology Megan Newcombe, with additional co-authors from the Carnegie Institution of Science.
“We wanted to understand how our planet managed to get water because it’s not completely obvious,” Newcombe said. “Getting water and having surface oceans on a planet that is small and relatively near the sun is a challenge”
The team of researchers analyzed seven melted, or achondrite, meteorites that crashed into Earth billions of years after splintering from at least five planetesimals—objects that collided to form the planets in our solar system. In a process known as melting, many of these planetesimals were heated up by the decay of radioactive elements in the early solar system’s history, causing them to separate into layers with a crust, mantle, and core.
Because these meteorites fell to Earth only recently, this experiment was the first time anyone had ever measured their water contents. UMD geology graduate student Liam Peterson used an electron microprobe to measure their levels of magnesium, iron, calcium, and silicon, then joined Newcombe at the Carnegie Instution for Science’s Earth and Planets Laboratory to measure their water contents with a secondary ion mass spectrometry instrument.
“The challenge of analyzing water in extremely dry materials is that any terrestrial water on the sample’s surface or inside the measuring instrument can easily be detected, tainting the results,” said co-author Conel Alexander, a scientist at the
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