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Mantle neon illuminates the formation of the earth

The artist's impression of a young star surrounded by a protoplanetic disk where planets are formed. Based on actions by…



The artist’s impression of a young star surrounded by a protoplanetic disk where planets are formed. Based on actions by neonisotopes, UC Davis researchers conclude that the earth was formed relatively quickly from this cloud of dust and gas, collecting water, carbon and nitrogen into the deep soil. Credit: European Southern Observatory

The Earth was formed relatively quickly from the cloud of dust and gas around the sun, catch water and gases in the planet’s cloak, according to research published December 5th in the journal Nature . In addition to settling the origins of the earth, work can help identify extrasolar systems that can support habitable planets.

Writing data from the depths of the earth into deep space, University of California Davis Professor Sujoy Mukhopadhyay and Postdoctoral Researcher Curtis Williams used neonisotopes to show how the planet was formed.

“We try to understand where and how the neon in the earth’s mantle was acquired, which tells how quickly the planet was formed and under what conditions,” Williams said.

Neon is actually a place for gases like water, carbon dioxide and nitrogen come from, Said Williams. Unlike these compounds necessary for life, the neon is an inert noble gas, and it is not affected by chemical and biological processes.

“So neon remembers where it came from after four and a half billion years , Says Mukhopadhyay.

There are three competing ideas about how the earth was formed from a protoplanetic disk of dust and gas over four billion years ago and how water and other gases were delivered to the growing earth. In the first, the planet grew relatively quickly over two to five million years and caught gas from the nebula, the whirling cloud of dust and gas surrounding the young sun. The second theory suggests that dust particles are formed and irradiated by the sun for a time before they are condensed in miniature objects called planetesimals, which were later delivered to the growing planet. In the third option, the soil formed relatively slowly and gases were supplied by carbonaceous condensate metrics rich in water, carbon and nitrogen.

These different models have consequences for how early the Earth was, Mukhopadhyay said. If the earth was formed quickly out of the sole of the sun, it would have had a lot of hydrogen at or near the surface. But if the earth was formed by carbonaceous condoms, its hydrogen had come in more oxidized form, water.

Deep Sea Neon Neon

To find out which of the three competing ideas on planetary formation and delivery of gases were accurate, Williams and Mukhopadhyay carefully determined the conditions of neonisotopes captured in the Earth’s mantel when the planet was formed. Neon has three isotopes, neon-20, 21

and 22. All three are stable and non-radioactive, but neon-21 is formed by radioactive decomposition of uranium. So the amounts of neon-20 and 22 in the earth have been stable since the planet was formed and will remain so forever, but the neon-21 slowly accumulates over time. The three scenarios of earth formation are predicted to have different relationships between neon-20 and neon-22.

The closest they could come to the mantle was to look at rocks called pillow base salts on the seabed. These stained-glass stones are the remains of deep-ground floods that smashed and cooled in the ocean, later collected by a drill run led by the University of Rhode Island, making its collection available to other researchers.

Gases are found in small bubbles in the basalt. With a press, Williams cracked basalt chips in a sealed chamber, allowing the gases to flow into a sensitive mass spectrometer.

Now for space. Earlier researchers determined the neonisotope ratio of the “solnebel” model (early fast-paced model) with data from the Genesis mission, which captured particles of solar wind. Data for the “irradiated particles” model came from analyzes of lunar soil and meteorites. Finally, carbonaceous chondrite meteorites gave data for the late accretion model.

Minimal size for a habitable planet

The isotopic ratios they found were way beyond those for the “irradiated particles” or “late accretion” models, Williams said and supported early formation.

“This is a clear indication that there is nebulary neon in the deep jacket,” Williams said.

No, remember, is a marker for the other volatile compounds. Hydrogen, water, carbon dioxide and nitrogen would have been condensed in the soil at the same time – all ingredients as far as we know go on creating a habitable planet.

The results involve absorbing these vital compounds, a planet must reach a certain size – Mars size or slightly larger – before the solar network disappears. Observations of other solar systems show that it takes about two to three million years, says Williams.

Is the same process about other stars happening? Observations from Atacama Large Millimeter Array or ALMA, the observatory in Chile suggest that it does, the researchers said.

ALMA uses a series of 66 radio telescopes that act as a single instrument for the use of dust and gas in the universe. It can see the planet-forming discs of dust and gas around some nearby stars. In some cases there are dark bands in the disks where dust has been emptied.

“There are a couple of ways that dust can be emptied from the disc, and one of them is that they form planets,” Williams says.

“We can observe planetary formation in a gas disk in other solar systems, and there is a similar description of our own solar system preserved in the earth’s interior,” said Mukhopadhyay. “This can be a common way for planets to form elsewhere.”


Explore further:
Plate tics may have been active on earth since the beginning

More information:
Curtis D. Williams et al. Capture of nebular gases during soil accretion is preserved in deep-shell neon, Nature (2018). DOI: 10,1038 / s41586-018-0771-1

Journal Reference:
Nature

Provided by:
UC Davis

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