![]() A new theory emerged: Comets could have carried water to early Earth. When the European Giotto spacecraft visited Halley’s Comet in 1986, researchers noticed its heavy water content was higher than the gas in Earth’s part of the early solar system. That idea, along with the planet’s high D/H ratio, led many to believe that Earth’s water must have arrived after Earth had cooled. Because the nebula was short-lived, most scientists suspect that Earth didn’t have enough time to collect these gases before they escaped into space. Around Earth, hydrogen and other elements could stick around only as a gas. The region near the star was too warm for some material to coalesce as ices, which instead formed in the outer part of the solar system. This material, known as the solar nebula, contained all the elements that built the planets, and the compositions varied with distance from the Sun. “At that point, I got very excited.”Įarth and the rest of the planets formed inside a nest of gas left over from the birth of the Sun. ![]() “I thought, wow, here’s a way we can actually measure the original fingerprints,” Meech says. But the University of Hawaii, where Meech is based, had just purchased a new ion microprobe that might be able to do the job. No one had investigated the D/H ratio in those samples because the technology to do so was new. That material may never have mixed with the stuff on the surface and could represent Earth’s early water. However, the geologist revealed that some rocky material brought up from Earth’s mantle does contain small traces of water. But after chatting with a geologist, she learned that the plumes actually came from more recent activity - they weren’t primordial after all. ![]() When Meech heard that primordial water could be spouting from the surface in Iceland, she grew excited at the chance to study the earliest flavor of water. All of these processes would give the modern Earth a higher D/H ratio compared with when the planet was newly formed. Geological processes, such as the evaporation of water from reservoirs such as lakes and oceans, can also change the ratio, as can biological reactions, because lighter isotopes are used differently than heavier ones in metabolic processes. Like most planets, Earth probably lost some of its atmosphere to space, and the lighter hydrogen would be easier to strip from the planet than its heavier counterpart. Reservoirs with a high quantity of heavy water have a high D/H ratio, while deuterium-poor reservoirs show a lower ratio.īut Earth’s ratio should have changed over time. Meech was suspicious of this idea because measurements of Earth’s deuterium-to-hydrogen (D/H) ratio, which is connected to the ratio of heavy water to normal, is generally based on the composition of today’s oceans. Today, most scientists believe asteroids carried water to the young, dry Earth. On Earth, the observed ratio is higher than it would have been in the young solar system, leading many astronomers to suspect that the water was imported because the ratio should remain constant over time. Normal hydrogen lacks a neutron, so water with deuterium weighs more than ordinary water.īy simulating conditions in the early solar system, researchers can calculate the ratio of heavy water to ordinary water when the planets were forming. One of those “flavors” is heavy water, a form of water that incorporates deuterium, an isotope of hydrogen whose nucleus contains one proton and one neutron. Most of that search has focused on sorting out the various isotopes of hydrogen that go into making the water - or “the flavor of water,” as Lydia Hallis of the University of Glasgow calls it. The source of Earth’s water has been a long-standing mystery Meech herself has been trying to solve it for at least 20 years. “Then she said, ‘This is probably primordial water,’ and it set a lightbulb off,” Meech says. The guide told the group not to worry - it was only water. On that fateful Icelandic tour, Meech saw geothermal areas with gas billowing out of the ground. But a field trip to Iceland in 2004 ultimately sent her scrambling through the craters of Hawaii nearly a decade later in search of clues about the liquid that helped birth life on this planet. An astronomer by trade, she is usually behind the telescope, investigating comets and looking for hints about how Earth got its water. Karen Meech doesn’t spend a lot of time digging through Earth’s rocks.
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