Xenon isotope constraints on the thermal evolution of the early Earth

The thermal regime of the Earth's interior during the Hadean (the first 700 My after the birth of the solar system) is subject to debate. Evidence for a hotter mantle stems from the abundance of magnesian lavas (komatiites) in the Archean, although their generation might have also resulted from different (hydrous) melting conditions. In this contribution, the present-day mantle abundances of xenon isotopes contributed by extinct and extant radioactivities are used to constrain thermal and magmatic evolution models of the early Earth. Results show that, in the Hadean, heat could escape at a rate much faster than Today. Heat loss from the mantle was driven by magmatism rather than by conduction through the lithospheric lid, precluding modern style plate tectonics. Around the Hadean–Archean transition, a drastic change in the thermal regime led to a secular cooling rate comparable to the modern one, in probable relation to the onset of plate tectonics. Our model also suggests that solid-state convection started later than 50 My after the formation of the solar system, a view consistent with proposed ages for the Moon-forming impact.