Abstract
The Earth has been releasing vast amounts of heat from deep Earth's interior to the surface since its formation, which primarily drives mantle convection and a number of tectonic activities. In this heat transport process the core-mantle boundary where hot molten core is in direct contact with solid-state mantle minerals has played an essential role to transfer thermal energies of the core to the overlying mantle. Although the dominant heat transfer mechanisms at the lowermost mantle is believed to be both conduction and radiation of the primary lowermost mantle mineral, bridgmanite, the radiative thermal conductivity of bridgmanite has so far been poorly constrained. Here we revealed the radiative thermal conductivity of bridgmanite at core-mantle boundary is substantially high approaching to ∼5.3±1.2 W/mK based on newly established optical absorption measurement of single-crystal bridgmanite performed in-situ under corresponding deep lower mantle conditions. We found the bulk thermal conductivity at core-mantle boundary becomes ∼1.5 times higher than the conventionally assumed value, which supports higher heat flow from core, hence more vigorous mantle convection than expected. Results suggest the mantle is much more efficiently cooled, which would ultimately weaken many tectonic activities driven by the mantle convection more rapidly than expected from conventionally believed thermal conduction behavior.
Highlights
The evolution of the planet Earth can be paraphrased as the history of cooling over the past 4.5 billion years since the Earth’s surface was fully covered with a deep magma ocean under extremely high-temperature conditions
Results suggest the mantle is much more efficiently cooled, which would weaken many tectonic activities driven by the mantle convection more rapidly than expected from conventionally believed thermal conduction behavior
A higher contribution of krad of Brg to the heat flow would support the view on core-mantle boundary (CMB) that is much more thermally and dynamically active than we have so far expected, which should likely stabilize the mantle upwelling rooted in the CMB and help to enhance more vigorous mantle convection. This newly obtained perspective implies that the Earth’s mantle is ∼1.5 times more efficiently cooled, which would weaken many tectonic activities driven by the mantle convection more rapidly than expected from the conventionally believed thermal conduction value (Lay et al, 2008)
Summary
The evolution of the planet Earth can be paraphrased as the history of cooling over the past 4.5 billion years since the Earth’s surface was fully covered with a deep magma ocean under extremely high-temperature conditions. A number of global dynamics in the Earth including mantle convection, plate tectonics and igneous activities have been driven by huge thermal energies released from deep Earth’s interior in the course of this cooling history. This perspective raises the question as to how fast the Earth has been losing heat throughout the Earth’s history, which directly links to the fundamental question on how long the Earth will remain dynamically active. Temperature condition just above CMB where the sharp rise in geothermal profile at mantle side is expected has been previously estimated to be ∼4100 K (Steinle-Neumann et al, 2001; Deschamps and Trampert, 2004; Manthilake et al, 2011).
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