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Friday 25 November 2011

Earth’s outer core ‘poor in oxygen’

Earth’s outer core ‘poor in oxygen’

London: Oxygen is the most abundant element in the planet, so it is not unreasonable to expect that it might be one of the dominant “light elements” in the core.

The composition of the Earth's core remains a mystery. Scientists know that the liquid outer core consists mainly of iron, but it is believed that small amounts of some other elements are present as well.

Now, a new research from a team including Yingwei Fei from Carnegie’s Geophysical Laboratory has revealed that oxygen does not have a major presence in the outer core.

This has major implications for our understanding of the period when the Earth formed through the accretion of dust and clumps of matter.

According to current models, in addition to large amounts of iron, the Earth's liquid outer core contains small amounts of so-called light elements, possibly sulfur, oxygen, silicon, carbon, or hydrogen.

The team provides new experimental data that narrow down the identity of the light elements present in Earth's outer core.

High-speed impacts can generate shock waves that raise the temperature and pressure of materials simultaneously, leading to melting of materials at pressures corresponding to those in the outer core.

The team carried out shock-wave experiments on core materials, mixtures of iron, sulfur, and oxygen. They shocked these materials to the liquid state and measured their density and speed of sound travelling through them under conditions directly comparable to those of the liquid outer core.

By comparing their data with observations, they conclude that oxygen cannot be a major light element component of the Earth’s outer core, because experiments on oxygen-rich materials do not align with geophysical observations.

This supports recent models of core differentiation in early Earth under more “reduced” (less oxidized) environments, leading to a core that is poor in oxygen.

Their work has been published Nov. 24 in Nature.


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