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Oxygen Concentrations in Earth's Core Higher Than Previously Thought, Researchers Say

Sep 23, 2015 11:18 AM EDT
This model shows planetesimals accumulating to form Earth 4.56 billion years ago.
(Photo : Antoine Pitrou/Globe University )

There is more oxygen in Earth's core than previously thought, say researchers from Lawrence Livermore National Laboratory, who add that this discovery may shed new light on Earth's formation.

Earth formed roughly 4.56 billion years ago from a cloud of dust, gases, and smaller planetesimals that combined. Earth's rocky metallic core formed first, with the densest material sinking to the center and lighter pieces creating the mantle and crust. Earth's mantle is composed of silicon oxide, or silicate. When this formation occurred, geophysical and geochemical signatures were left behind and remain today.

Researchers discovered a higher oxygen concentration in the Earth's core by examining these geophysical and geochemical signatures of Earth's core and mantle together, according to a news release. This higher oxygen concentration signifies that Earth has accumulated materials that are more oxidized than the present-day mantle, the researchers noted. Materials become oxidized when they combine chemically with oxygen, whereas when they lose oxygen, they undergo reduction. This is also known as a redox reaction.

While previous studies have tried to explain core formation using the geochemical and geophysical signatures separately, this new study examines them jointly. In doing so, they found that instead the Earth's core formed in a hot, deep, liquid magma ocean, under higher oxidized conditions than present day Earth.

"This new model is at odds with the current belief that core formation occurred under reduction conditions," Rick Ryerson, a Lawrence Livermore geologist, explained in a statement. "Instead we found that Earth's magma ocean started out oxidized and has become reduced through time by oxygen incorporation into the core."

Another way to understand the oxidation and reduction reactions is to think of oxidation as the losing of electrons and reduction as the gaining of electrons. So over time, oxygen has been released into the core through these processes.

Their findings were recently published in the journal Proceedings of the National Academy of Sciences.

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