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The thermal state of the early Earth's interior and its way of cooling are crucial for its subsequent evolution. Earth is initially hot as it acquired enormous heat in response to violent processes during its formation, e.g., the Moon-forming giant impact, the segregation and formation of its metallic core, the tidal interaction with the early Moon, and the decay of radioactive elements, etc. In the meantime, the cooling mechanisms of early Earth's mantle remain elusive despite their importance, and the previously proposed cooling models of the mantle are controversial. In this paper, we first reviewed several prevalent parameterized thermal evolution models of the early mantle. The models give unrealistic predictions since they were established solely based on a single tectonic regime, such as the stagnant-lid regime, or relied on the disputable existence of the plate tectonics prior to ~ 3.5 Ga. Then we argue that the mantle should have started to cool down from a very hot state after the solidification of the ferocious magma ocean. Instead of using one single scaling law to describe a single-stage model, we suggest that an episodic multi-stage cooling model (EMCM) of the early mantle could be more plausible to account for the mantle's early cooling process. The model reconciles with the fact that the mantle cools down from a hot state prior to ~ 3.5 Ga and can also explain the well-constrained post-3.5 Ga thermal history of the mantle. [ABSTRACT FROM AUTHOR]

The Earth's core is composed of iron, nickel, and a small amount of light elements (e.g., Si, S, O, C, N, H and P). The thermal conductivities of these components dominate the adiabatic heat flow in the core, which is highly correlated to geodynamo. Here we review a large number of studies on the electrical and thermal conductivity of iron and iron alloys and discuss their implications on the thermal evolution of the Earth's core. In summary, we suggest that the Wiedemann–Franz law, commonly used to convert the electrical resistivity to thermal conductivity for metals and alloys, should be cautiously applied under extremely high pressure–temperature (P–T) conditions (e.g., Earth's core) because the Lorentz number may be P–T dependent. To date, the discrepancy in the thermal conductivity of iron and iron alloys remains between those from the resistivity measurements and the thermal diffusivity modeling, where the former is systematically larger. Recent studies reconcile the electrical resistivity by first-principles calculation and direct measurements, and this is a good start in resolving this discrepancy. Due to an overall higher thermal conductivity than previously thought, the inner core age is presently constrained at ~1.0 Ga. However, light elements in the core would likely lower the thermal conductivity and prolong the crystallization of the inner core. Meanwhile, whether thermal convection can power the dynamo before the inner core formation depends on the amounts of the proper light elements in the core. More works are needed to establish the thermal evolution model of the core. [ABSTRACT FROM AUTHOR]

The lunar ferroan anorthosites, formed by plagioclase flotation from the crystallization of the lunar magma ocean, have an age span of over ~ 200 Ma. However, previous thermal models predicted a much shorter time range. We propose that a much smaller thermal conductivity of anorthositic crust due to its high porosity may have delayed the solidification of the lunar magma ocean. Our thermal simulation results, using the thermal conductivity of porous lunar crust, show that crystallization of a 1000 km deep magma ocean could be prolonged to tens of millions of years, and up to 180 Ma under some extreme conditions. The porous crust alone can't explain the large crustal age span, however. Other circumstances must be taken into consideration, such as a thick lunar soil. [ABSTRACT FROM AUTHOR]