The primordial water was fortuitously sealed in tiny glass pockets trapped inside the mineral olivine, bits of which were later incorporated into volcanic rocks found on Padloping Island, northwest of Canada’s Baffin Island, and in Iceland.
The glass itself is microscopic, roughly 0.0008 inches, or 20 micrometers, in diameter and it contains just a trace amount of water.
“The measurements are extremely difficult to make. Only in the past few years has the technology developed enough to measure such low concentrations of water inside such small amounts of material,” Lydia Hallis, a cosmochemist at the University of Hawaii, told Discovery News.
Using the school’s newly purchased ion microprobe, Hallis and colleagues were able to ferret out a telltale ratio of deuterium-to-hydrogen isotopes in the water. A deuterium atom, also known as “heavy hydrogen” has an extra neutron, while the far more common hydrogen atom has just a proton and an electron.
The ratio of deuterium to hydrogen, abbreviated as D/H, is considered a key diagnostic -- but not the only one -- of where in the solar system a body was made. That is because deuterium, which was created in the Big Bang explosion, was not spread evenly throughout the disk of gas and dust that surrounded the young sun and from which the planets and other bodies were were formed.
The D/H ratio also is an indication of chemical processes over time. For example, lighter-weight hydrogen atoms in the atmosphere can more easily escape to space than slightly beefier deuterium isotopes. A range of D/H ratios are found on Earth due to hydrological cycles.
The source of Earth’s water has been a long-standing debate.
“It’s a very complex story,” University of Hawaii astronomer Karen Meech told Discovery News. “It’s going to take a whole bunch of measurements before we can make any conclusions.”
Some scientists believe that whatever water existed in dust grains which eventually came together to form Earth would have been vaporized and released into space during the massive impact that led to the creation of the moon. Those theories rely on water-rich comets and/or asteroids later smashing into the planet to create the oceans.
Other computer models show Earth’s original water may have remained in the atmosphere after the moon-forming impact and then returned to the surface as the planet cooled.
“I think our data points towards most of Earth’s water being present from its formation, but we can’t rule out that later addition of material also added some water to Earth’s surface and upper mantle reservoirs,” Hallis wrote in an email.
“What we can say is that the deep mantle water measured in our samples would have been isolated from this addition, as none of the later impacts would have been large enough to penetrate down to that level in the Earth,” she added.
The work has implications for all the rocky bodies in the solar system, as well as planetary systems beyond.
“If we accept that water is retained from the accretion process, rather than all being boiled away and having to be added again later, then it implies this would happen during the formation of other rocky bodies, so water should be present (and abundant) in these other bodies,” Hallis said.
“The recent measurements and images from Mars support this, showing that despite the loss of most of its atmosphere (thus a huge amount of water) sub-surface ice is still present on Mars, and even liquid water still exists,” she wrote.
Read more at Discovery News
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