Onset of habitable conditions on the Hadean Earth set by feedback between tides and greenhouse forcing

TL;DR

This work investigates whether tidal heating from Earth–Moon interactions, coupled to atmospheric greenhouse forcing and mantle redox, can extend the Hadean magma ocean and produce periods of global radiative equilibrium. Using the PROTEUS framework to couple interior convection (SPIDER) with an atmospheric radiative–convective model (AGNI) and a tunable tidal heat source, the authors map how varying $H_{\text{tide}}$, $f\mathrm{O}_2$, and volatile inventories alter solidification timescales and atmospheric composition. They find that GRE epochs can persist from ~1.5 to >300 Myr across a broad parameter space, with oxidizing atmospheres delaying cooling through late $H_2O$ outgassing and reducing atmospheres fostering $H_2$- and $CH_4$-rich envelopes; tidal efficiency itself becomes a strong function of atmospheric state, challenging fixed-$Q$ assumptions. The results imply tidal–greenhouse feedbacks could have extended habitable conditions and prebiotic chemistry windows on the early Earth, tying planetary interior dynamics to the emergence of life-supporting environments.

Abstract

In the aftermath of the Moon-forming giant impact, the Hadean Earth's mantle and surface crystallized from a global magma ocean blanketed by a dense volatile-rich atmosphere. While prior studies have explored the thermal evolution of such early Earth scenarios under idealized, oxidizing conditions, the potential feedback between tidal heating driven by Earth--Moon orbital forcing and variable redox scenarios have not yet been explored in detail. We investigate whether tidal heating could have prolonged this early magma ocean phase and supported quasi-steady state epochs of global radiative equilibrium: periods of thermal balance between outgoing radiation and interior heat flux. Using the $\texttt{PROTEUS}$ simulation framework, we simulate Earth's early evolution under a range of plausible tidal power densities, oxygen fugacities, and volatile inventories. Our results suggest that feedback between tidal heating and atmospheric forcing can induce substantial variation in magma ocean lifetimes, from $\sim$30 Myr up to $\sim$500 Myr, sensitive to interior redox conditions. Global radiative equilibrium epochs commonly arise across this range, lasting from $\sim$2 to $\sim$320 Myr, and typically occur from 24 Myr after the Moon-forming impact. Under oxidizing conditions, late-stage H$_2$O degassing promotes melt retention and sustained heating due to its significant contribution to greenhouse forcing. Weak tides increase the atmospheric abundance of H$_2$S and NH$_3$ and deplete CO. Therefore, the feedback between tides and atmospheric forcing induces a disequilibrium signature in the magma ocean atmosphere.

Figures (9)

• Figure 1: Simulation results for nominal abundance and $f$O$_2 = \Delta \mathrm{IW} + 0$ across all tidal power densities (see Section \ref{['sec:cases']}). The horizontal axis shows time [yr] since the Moon-forming impact on a logarithmic scale. Panel A: evolution of the rheological front (vertical axis: mantle depth fraction). Panel B: extracted timelines for each case (vertical axis: case label). Dotted lines trace cumulative tidal energy dissipation; marker size scales with total dissipated energy. Solid lines indicate tidal heat-supported GRE; black markers ($\pmb |$) denote volume mixing ratio extraction times ('VMR time'). Crosses ($\times$) mark mantle solidification ($\phi < 0.005$).
• Figure 2: Simulated atmospheric compositions (expressed as normalized volume mixing ratio, VMR) for cases with nominal elemental abundances and $f$O$_2 = \Delta \mathrm{IW} + 0$, across all considered tidal power densities (see Section \ref{['sec:cases']}). The horizontal axis denotes the time after model initialization. The horizontal axis represents four axis stitched together, each leading up to their corresponding VMR time (Figure \ref{['fig:Rheo_tide_timeline']}B). Cases transition smoothly across this plot because they all attain similar compositions in their evolution, only deviating from the case without tidal heating when tides maintain different non-zero melt fractions. Weaker tides become active later, and so these cases reach similar compositions as their stronger tidally heated counterparts, but sooner. The dotted vertical lines in the shaded region represent the start of GRE epochs, demonstrating that the atmosphere composition remains unchanged in the absence of escape processes.
• Figure 3: Global melt fraction $\phi$ during global radiative equilibrium (at $t_\mathrm{VMR}$) as a function of $\log_{10}(f\mathrm{O}2/\Delta$IW) for a range of tidal power densities $H_\text{tide}$ (marker color) [W.kg^-1] and critical melt fraction $\phi_\text{crit}$ (marker shape).
• Figure 4: Evolution of nominal-composition cases across the full range of $f$O$_2$ and tidal power densities simulated (see Section \ref{['sec:cases']}). Panel A (left): stages in planet's lifetime after model initialization. Dotted lines trace cumulative tidal heat dissipation; marker size increases with total dissipated energy. Solid lines indicate tidally-supported GRE states; black vertical bars ($\pmb |$) mark $t_\mathrm{VMR}$. Crosses ($\times$) denote solidification, defined at $\phi < 0.005$. Panel B (right): volume mixing ratios of volatiles at $t_\mathrm{VMR}$.
• Figure 5: Net atmospheric energy flux, by which the planet loses heat to space balanced against tides during GRE. Plotted at time $t_\mathrm{VMR}$ as a function of $\log_{10}(f\mathrm{O}2/\Delta$IW) for different tidal power densities $H_\text{tide}$ and $\phi_\text{crit}$.