Scientists therefore assumed that newborn Earth must have formed from dry material and acquired its water through bombardment by objects from more distant, icy reaches of the solar system.
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That suggests comets or asteroids may not have been the major source of our planet’s water. Hallis says that the initial belief was that heat that was produced during this accretion process made Earth extremely hot that boiled off all the remaining water which was then replaced later by asteroid and comet impacts.
Planetary scientists at the University of Hawaii in a new study report the first ever evidence of ancient dust saturated with water collected at the heart of an infant Earth. He adds, “And it wasn’t added by comets”.
Researchers now confirm that deep inside the Earth’s mantle lies hydrogen composition from primordial water that matches the composition of the proto solar disk before any planets existed in the solar system. Evidence for this explanation can be found in a new paper published on Thursday in the journal Science. Scientists questioned whether the first water molecules were held by the ancient minerals present in the deep mantle, 1,800 miles or 2,900 kilometers deep below Earth’s surface. And lava sampled in 1985 from Baffin Island in the Canadian Arctic originated from just the right depth to provide answers.
“Only in the past few years has the technology developed enough to measure such low concentrations of water inside such small amounts of material”, said Hallis, now a research fellow at the University of Glasgow in Scotland.
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.
The team examined the ratios of two isotopes of hydrogen – ordinary hydrogen and the heavier deuterium – either of which can pair with hydrogen and oxygen to form water.
Uncovering which region supplied Earth’s water requires collecting H2O molecules left over from the planet’s deep past. “Hydrogen is everywhere on Earth!”
“Earth is a very water-rich planet both inside and on the surface”, Hallis says. However, if the planet managed to keep water from the solar nebula before it evaporated away, there’s no reason other planets couldn’t do the same thing. This eruption was fed directly from the Iceland mantle plume, and a proportion of the gas emitted is thought to be water vapor sourced from this plume. The ratio of the isotopes can serve as a signature of water’s origin.
Geologists can track where water comes from within the solar system by studying the ratio of deuterium, also known as heavy hydrogen, to normal hydrogen in the water molecules, because different sources have different ratios.
According to led author of the study, Lydia Hallis from the University of Hawaii’s NASA Astrobiology Institute and the University of Glasgow, these new measurements are suggesting that Earth apparently possessed water during the very start of the planet formation where water originally formed inside the proto solar disk.
About 4.6 billion years ago, Earth came into form as dust and rocks around the sun collided. Being spread unevenly during the formation of stellar dust, that contributed to the formation of the planets, by measuring the levels of deuterium, we can establish, with a marginal error, the place where every planed formed in our solar system.
These early rocks contained surprisingly little deuterium: a ratio almost 22 per cent less than in seawater today.
But, “We’re in the beginnings of understanding this and we’re very far from saying this is definitely what happens”, Hallis says.
Hallis said lava samples had to come from deep in the mantle because lava closer to the crust may have erupted and mixed with surface matter.
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Instead, the ratio suggests that the water must have originated in the dust cloud from which the sun and planets originally condensed.
