Other
Scientific paper
May 2008
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2008agusmgp33a..02t&link_type=abstract
American Geophysical Union, Spring Meeting 2008, abstract #GP33A-02
Other
1507 Core Processes (1213, 8115), 1521 Paleointensity, 1595 Planetary Magnetism: All Frequencies And Wavelengths, 8124 Earth'S Interior: Composition And State (1212, 7207, 7208, 8105)
Scientific paper
The strength of Earth's early magnetic field is important for understanding the evolution of the core, surface environment, atmosphere and life. Paleointensity analyses of single silicate crystals indicate that the strength of the geomagnetic field 3.2 billion years ago was within 50% of the modern value (Tarduno et al., 2007), but for even earlier times it is unknown. Two ideas have been offered: (1) the geomagnetic field started shortly after core formation, and the subsequent field strength has been within a factor of 2-3 of the modern value since its initiation; (2) the field was at null values ~3.9 billion years ago and commenced thereafter. The latter scenario relies on a hypothesis to explain the amount and isotopic composition of nitrogen found in soils of the Moon; this lunar nitrogen may have been derived from Earth's atmosphere via the solar wind (Ozima et al., 2005) in the absence of geomagnetic field that would otherwise shield atmospheric erosion. The possibility of a delayed dynamo onset (Labrosse et al., 2007) will be discussed, as will our efforts to address the presence/absence of the geomagnetic field between 3.2 and 3.9 billion years ago using the terrestrial rock record. The available constraints on ancient magnetic shielding will be reviewed in light of the radiation and particle flux associated with the active young Sun. (References: Labrosse et al., A crystallizing dense magma ocean at the base of the Earth's mantle, Nature, 450, 866-868, 2007; Ozima, M., et al., Terrestrial nitrogen and noble gases in lunar soils, Nature, 436, 655-659, 2005; Tarduno, J.A. et al., Geomagnetic field strength 3.2 billion years ago recorded by single silicate crystals, Nature, 446, 657-660, 2007.)
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