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Palaeomagnetic field intensity variations suggest Mesoproterozoic inner-core nucleation
A J Biggin1, E J Piispa2, L J Pesonen3
1Department of Earth, Ocean and Ecological Sciences, University of Liverpool, Liverpool L69 7ZE, UK.
Nature
|October 10, 2015
Summary
The Earth's inner core began growing about 1 to 1.5 billion years ago, marking a key moment in planetary evolution. This finding, based on paleomagnetic data, supports a simple model of Earth's thermal history.
Area of Science:
- Geophysics
- Planetary Science
- Paleomagnetism
Background:
- The Earth's inner core grows via the solidification of liquid iron.
- Estimates for the timing of inner core nucleation vary widely (0.5 to 2 billion years ago) due to differing thermal conductivity values.
- Inner core nucleation significantly impacts planetary thermal evolution and the geodynamo.
Purpose of the Study:
- To refine the timing of Earth's inner core nucleation.
- To investigate long-term variations in geomagnetic field strength.
- To provide evidence supporting specific models of Earth's thermal evolution.
Main Methods:
- Analysis of an expanded Precambrian paleomagnetic intensity database.
- Application of new reliability criteria for selecting paleomagnetic data.
- Examination of geomagnetic field strength and variability over geological timescales.
Main Results:
- The study provides intensity-based support for the Precambrian field's dipolarity.
- Firm evidence for very long-term variations in geomagnetic strength was found.
- A significant increase in average field strength and variability occurred between 1 and 1.5 billion years ago.
Conclusions:
- The observed transition in geomagnetic field strength strongly suggests inner core nucleation occurred between 1 and 1.5 billion years ago.
- This timing supports a modest core thermal conductivity value.
- The findings are consistent with a simple thermal evolution model for Earth.
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