Lunar Heating: How Tides Prolonged Earth's Magma Ocean express
After the Moon's birth, Earth resembled a sizzling lump of dough: a continuous liquid magma and a dense shroud of gases. The Moon acted like a giant spoon, constantly kneading this lump with its gravity. Friction generated heat, delaying cooling. Scientists calculated: depending on tidal strength and oxygen content inside, the ocean of molten rock lasted from 30 to 500 million years. When oxygen was scarce, carbon turned into carbon monoxide. With an excess, water vapor enveloped the planet like a kitchen towel, holding in the heat. Weak tides added gases rich in hydrogen — ammonia and hydrogen sulfide. Eventually, Earth, like dough on a table, reached equilibrium: as much energy came in as went out. Such periods lasted up to 320 million years. If tidal friction had been weaker, the ocean would have solidified in 30 million years, and solid crust would have appeared half a billion years earlier: this could have changed the planet's entire history.
Original abstract
as written by the authors arXiv:2511.00952
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.
Earth's magma ocean existed longer than the time from the first dinosaurs to today — nearly half a billion years.