Innermost inner core

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For broader coverage of this topic, see Inner core

The Earth has a solid inner core, distinct from its liquid outer core.[1]

Existence of an Innermost Inner Core was proposed by Adam Dziewonski and Miaki Ishii to explain the discrepancies in certain fit to travel-time wave models of the Inner Core.[2] The status of the Innermost Inner Core as a distinct entity is contested.[3] Detractors argue that anomalous data can be explained with other methods.[3]

Proposed models[]

The Innermost Inner Core model proposes a distinct laterally homogeneous anisotropic sphere within the Inner Core.[2]

Earth's solid Inner Core.

Estimates differ on the size of the Innermost sphere. Dziewonski and Ishii call for a radius of 300 km.[2] Trampert et. al. put forth a different model, with a radius of 400 km.[4]

Implications[]

The existence of distinct anisotropic spheres within the Inner Core would represent evidence of two distinct periods of Inner Core formation.[2][4] It has also been theorized that the anisotropy observed represents an unknown phase change in iron.[2] Understanding the anisotropic structure of the innermost inner core would be an important constraint on inner core composition.

Other explanations[]

In 2012, Lythgoe et. al. proposed the existence of anisotropic hemispheres within the Inner Core as an alternative to the Innermost Inner Core theories.[3] The study suggests that Ishii et. al.'s conclusions were due to faulty statistical analysis, and claims the data are best described by hemispheric anisotropy.

References[]

  1. ^ Brush, Stephen G. (September 1980). "Discovery of the Earth's core". American Journal of Physics. 48 (9): 705–724. doi:10.1119/1.12026. ISSN 0002-9505.
  2. ^ a b c d e Ishii, Miaki; Tromp, Jeroen; Dziewoński, Adam M.; Ekström, Göran (2002). "Joint inversion of normal mode and body wave data for inner core anisotropy 1. Laterally homogeneous anisotropy". Journal of Geophysical Research: Solid Earth. 107 (B12): ESE 20–1–ESE 20-16. doi:10.1029/2001JB000712. ISSN 2156-2202.
  3. ^ a b c Lythgoe, K. H.; Deuss, A.; Rudge, J. F.; Neufeld, J. A. (2014-01-01). "Earthʼs inner core: Innermost inner core or hemispherical variations?". Earth and Planetary Science Letters. 385: 181–189. doi:10.1016/j.epsl.2013.10.049. ISSN 0012-821X.
  4. ^ a b Trampert, Jeannot; Beghein, Caroline (2003-01-24). "Robust Normal Mode Constraints on Inner-Core Anisotropy from Model Space Search". Science. 299 (5606): 552–555. doi:10.1126/science.1078159. ISSN 0036-8075. PMID 12543971.
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