The solubility of heat-producing elements in Earth’s core

Abstract

The long term thermal and dynamic evolution of Earth's core depends on its energy budget, and models have shown that radioactive decay due to K and U disintegration can contribute significantly to core dynamics and thermal evolution if substantial amounts of heat-producing elements are dissolved in the core during differentiation. Here we performed laser-heated diamond anvil cell experiments and measured K and U solubility in molten iron alloy at core formation conditions. Pyrolitic and basaltic silicate melts were equilibrated with metallic S-Si-O-bearing iron alloys at pressures of 49 to 81 GPa and temperatures of 3500 to 4100 K. We found that the metal-silicate partitioning of K is independent of silicate or metal composition and increases with pressure. Conversely, U partitioning is independent of pressure and silicate composition but it strongly increases with temperature and oxygen concentration in the metal. We subsequently modelled U and K concentration in the core during core formation, and found a maximum of 26 ppm K and 3.5 ppb U dissolved in the core, producing up to 7.5 TW of heat 4.5 Gyr ago. While higher than previous estimates, this is insufficient to power an early geodynamo, appreciably reduce initial core temperature, or significantly alter its thermal evolution and the (apparently young) age of the inner core.

Ab Initio Prediction of Potassium Partitioning Into Earth's Core

“…Gessmann and Wood () suggested that temperature enhances potassium incorporation into iron alloys. This was supported experimentally by Murthy et al () and Watanabe et al (), although no obvious temperature dependence was observed in other studies (Blanchard et al, ; Corgne et al, ). In this study, the temperature influence on the potassium partitioning is investigated by conducting calculations at 3,000 and 5,000 K at the constant pressure of 20 GPa, where the compositions of silicate and metallic systems are set to (MgSiO 3 ) 16 and Fe 50 , respectively.…”

“…The amount of potassium that can be incorporated into the core is determined by its partitioning between silicate and metallic systems. A number of laboratory experiments have therefore been performed to measure the metal/silicate partitioning coefficient of potassium (e. g., Blanchard et al, ; Bouhifd et al, ; Chabot & Drake, ; Corgne et al, ; Gessmann & Wood, ; Murthy et al, ; Watanabe et al, ). However, the results scatter significantly (by four orders of magnitude) potentially due to wide variations of the potassium partitioning depending on temperature, pressure, composition, and/or oxygen fugacity.…”

Ab Initio Molecular Dynamics Investigation of Molten Fe–Si–O in Earth's Core

“…But those same experiments (e.g., Badro et al, 2016Badro et al, , 2018Blanchard et al, 2017;Bouhifd & Jephcoat, 2011;Chidester et al, 2017;Du et al, 2017;Fischer et al, 2015;Huang & Badro, 2018;Jackson et al, 2018;Ricolleau et al, 2011;Siebert et al, 2012Siebert et al, , 2013Tsuno et al, 2013) have not observed any SiO 2 exsolution and even support that the present-day core could be undersaturated in Si and O (Brodholt & Badro, 2017). But those same experiments (e.g., Badro et al, 2016Badro et al, , 2018Blanchard et al, 2017;Bouhifd & Jephcoat, 2011;Chidester et al, 2017;Du et al, 2017;Fischer et al, 2015;Huang & Badro, 2018;Jackson et al, 2018;Ricolleau et al, 2011;Siebert et al, 2012Siebert et al, , 2013Tsuno et al, 2013) have not observed any SiO 2 exsolution and even support that the present-day core could be undersaturated in Si and O (Brodholt & Badro, 2017).…”

Magnesium Partitioning Between Earth's Mantle and Core and its Potential to Drive an Early Exsolution Geodynamo

“…It is noteworthy that the uncertainties (error bars plotted only for the present data + data from Badro et al, ) are on the same order as the scatter in the data, which is statistically self‐consistent. The orange data points labeled as “This study (*)” are reanalyses of previous experiments (Blanchard et al, ).…”