Innermost inner core
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Earth is proposed to have an innermost inner core, distinct from its inner core. It is surrounded by the inner core, and is composed of solid iron in a different, but unknown structure from the inner core.
The existence of an inner core was proposed by Adam Dziewonski and Miaki Ishii to explain the discrepancies in certain fits to travel-time wave models of the inner core.[1] It is contested whether the innermost inner core is a distinct entity, and it is claimed that the data can be explained in other ways.[2]
Proposed models[edit]
The innermost inner core model proposes a distinct laterally homogeneous anisotropic sphere within the inner core.[1]
Estimates differ on the size of the innermost core. Dziewonski and Ishii think a radius of 300 km.[1] Trampert et al. propose a different model, with a radius of 400 km.[3]
Implications[edit]
The existence of distinct anisotropic spheres within the inner core would represent evidence of two distinct periods of inner-core formation.[1][3] It has also been theorized that the anisotropy observed represents an unknown phase change in iron.[1] Understanding the anisotropic structure of the innermost inner core would be an important constraint on the inner core's composition.
Other explanations[edit]
In 2012, Lythgoe et al. proposed the existence of anisotropic hemispheres within the inner core as an alternative to the innermost inner core theories.[2] 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[edit]
- ^ 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. Bibcode:2002JGRB..107.2379I. doi:10.1029/2001JB000712. ISSN 2156-2202.
- ^ a b 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. Bibcode:2014E&PSL.385..181L. doi:10.1016/j.epsl.2013.10.049. ISSN 0012-821X.
- ^ 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. Bibcode:2003Sci...299..552B. doi:10.1126/science.1078159. ISSN 0036-8075. PMID 12543971. S2CID 7327843.