Innermost inner core

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. 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. 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. 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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