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Stratified by a sunken impactor

Nature Geoscience volume 9, pages 734–735 (2016)Cite this article

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There is potential evidence for a stratified layer at the top of the Earth's core, but its origin is not well understood. Laboratory experiments suggest that the stratified layer could be a sunken remnant of the giant impact that formed the Moon.

The core of the Earth is divided into a solid inner core and a liquid outer core. Changes in the Earth's magnetic field over short timescales1 and thermal properties of an iron alloy2 suggest the presence of a stratified layer at the top of the outer core. Recent seismic observations indicate that the layer may be less dense than the rest of the liquid core, and around 300 km thick3. Although controversial4, this seismological model could have implications for the Earth's formation and evolution, but there is no general consensus as to how a stratified layer could have formed. Such a layer has previously been attributed either to the transport of light elements to the core from the mantle by chemical interactions5, or to the accumulation of light elements at the top of the core associated with the crystallization of the solid inner core6. But both models struggle to generate a thick enough layer. Writing in Nature Geoscience, Landeau et al.7 instead hypothesize, on the basis of laboratory experiments, that the stratified layer is a remnant of the impactor that struck the Earth to form the Moon approximately 4.5 billion years ago.

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Figure 1: Formation of a stratified layer at the top of the Earth's core following the Moon-forming impact.

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Authors and Affiliations

  1. Miki Nakajima is in the Department of Terrestrial Magnetism, Carnegie Institution for Science, 5241 Broad Branch Road NW, Washington DC 20015, USA,

    Miki Nakajima

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  1. Miki Nakajima
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Correspondence to Miki Nakajima.

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Nakajima, M. Stratified by a sunken impactor. Nature Geosci 9, 734–735 (2016). https://doi.org/10.1038/ngeo2815

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