THE 187RE - 187OS AGE OF THE EARTH’S INNER CORE – GRAVITATIONAL CORE COLLAPSE AND R-PROCESS?

The age of the earth’s inner core is still heavily debated in the academic literature [1]. It depends mainly on the assumptions concerning the thermochemical parameters used in the calculations. Estimates vary from 0.6 Gyr [1] to 2.7 Gyr [2], with 1 Gyr [3] being still the currently most accepted value. Here I propose a model to constrain the age of the inner core independent from thermochemical parameters. For this, the concept of sudden nucleosynthesis [4, 5] is applied to explain peculiar terrestrial ¹⁸⁷Re - ¹⁸⁷Os isotopic signatures. Sudden nucleosynthesis has been suggested by nuclear theory as a possible mechanism for the creation of heavy elements such as Rhenium and Osmium. Hence, this concept might generally be used to identify rapid neutron-capture process (r-process) events in the past and thus become an additional promising approach in constraining the formation and / or activity of the earth’s inner core in the light of what is called “particle geophysics” [6]. For example, nuclear geochronometric Rhenium-Osmium model age calculations for published Pyroxenite and Komatiite data constrain one or more r-process event(s) between 2.5 Gyr and 3 Gyr ago. Since an r-process requires high neutron densities and temperatures within seconds, a gravitational core collapse around 3 Gyr forming at least a large part of the inner core is preliminarily proposed as a possible triggering event. Although this result is in contrast to the most accepted value of 1 Gyr [3] for the age of the inner core, it is in line with the proposed value of 2.7 Gyr, pronounced changes in the magnitude of the geomagnetic field and geological evidence like the onset of extensive plutonism and continental crust formation starting around the Archean-Proterozoic transition [2]. What triggered the proposed core collapse itself remains an open question, which one might be able to answer in future by constraining the analysis and interpretation of geochemical data with nuclear geochronometry and particle geophysics.

[1] Deuss (2014) Annu. Rev. Earth Planet Sci. 42, 103-126. [2] Hale (1987) Nature 329, 233 -237. [3] Labrosse et al. (2001) Earth Planet Sci. Lett. 190, 111 – 123. [4] Burbidge et al. (1957) Revs. Mod. Phys. 29, 547 – 650. [5] Hoyle & Fowler (1960) ApJ 132, 565 – 590. [6] Tanaka (2014) Annu. Rev. Earth Planet Sci. 42, 535 – 549.