Habitability of the early Earth: liquid water under a faint young Sun facilitated by strong tidal heating due to a closer Moon

Abstract

Geological evidence suggests liquid water near the Earth’s surface as early as 4.4 gigayears ago when the faint young Sun only radiated about 70% of its modern power output. At this point, the Earth should have been a global snowball if it possessed atmospheric properties similar to those of the modern Earth. An extreme atmospheric greenhouse effect, an initially more massive Sun, release of heat acquired during the accretion process of protoplanetary material, and radioactivity of the early Earth material have been proposed as reservoirs or traps for heat. For now, the faint-young-Sun paradox persists as an important problem in our understanding of the origin of life on Earth. Here, we use the constant-phase-lag tidal theory to explore the possibility that the new-born Moon, which formed about 69 million years (Myr) after the ignition of the Sun, generated extreme tidal friction—and therefore, heat—in the Hadean and possibly the Archean Earth. We show that the Earth–Moon system has lost $${\sim }3~{\times }~10^{31}$$ ∼ 3 × 10 31 J (99% of its initial mechanical energy budget) as tidal heat. Tidal heating of $${\sim }10\,\mathrm{W\,m}^{-2}$$ ∼ 10 W m - 2 through the surface on a time scale of 100 Myr could have accounted for a temperature increase of up to $$5\,^\circ $$ 5 ∘ C on the early Earth. This heating effect alone does not solve the faint-young-Sun paradox but it could have played a key role in combination with other effects. Future studies of the interplay of tidal heating, the evolution of the solar power output, and the atmospheric (greenhouse) effects on the early Earth could help in solving the faint-young-Sun paradox.

Toward RNA Life on Early Earth: From Atmospheric HCN to Biomolecule Production in Warm Little Ponds

“…where T eq is equilibrium temperature, A is albedo, L e is solar luminosity, σ is the Stefan-Boltzmann constant, and a is the semimajor axis of the planet. Luminosities for the Sun at 4.4 bya (0.705 L e ) and 4.0 bya (0.728 L e ) are obtained from a precomputed stellar evolution model of a Sun-like star (Heller et al 2020;Baraffe et al 2015). The Hadean Earth would have been mostly covered in water; therefore, albedo is taken to be 0.06, which is consistent with a cloudless water world (Roesch et al 2002).…”

“…We compute two habitable P-T profiles for each model by slightly adjusting the methane content and/or surface pressure. The luminosity, UV intensity, and asteroid bombardment rate at each epoch are based on stellar evolution models (Heller et al 2020;Baraffe et al 2015), observations of solar analogs (Ribas et al 2005), and the lunar cratering record (Chyba 1990), respectively.…”

Cloud Feedback on Earth's Long‐Term Climate Simulated by a Near‐Global Cloud‐Permitting Model

“…The increase of greenhouse gas contents, such as CO 2 and CH 4 , is likely responsible for the faint young Sun problem (FYSP) (e.g., Byrne & Goldblatt, 2014; Le Hir et al., 2014; Wolf & Toon, 2013; Wordsworth & Pierrehumbert, 2013). Other factors or feedbacks may have also contributed to solving this problem, such as a different atmospheric pressure, a less continent coverage, N‐H 2 collision‐induced warming, and a stronger tidal heating induced by the closer Moon (Goldblatt & Zahnle, 2011; Goldblatt et al., 2009; Heller et al., 2021; Rosing et al., 2010; Wordsworth & Pierrehumbert, 2013). A recent study of Goldblatt et al.…”

“…The increase of greenhouse gas contents, such as CO 2 and CH 4 , is likely responsible for the FYSP (e.g., Wolf and Toon (2013); Byrne and Goldblatt (2014); Le Hir et al (2014)). Other factors or feedbacks may have also contributed to solving this problem, such as a different atmospheric pressure, a less continent coverage, N 2 -H 2 collision-induced warming, and a stronger tidal heating induced by the closer Moon (Goldblatt et al, 2009;Rosing et al, 2010;Goldblatt & Zahnle, 2011;Wordsworth & Pierrehumbert, 2013;Heller et al, 2021). A recent study of Goldblatt et al (2021) suggested that a long-term cloud feedback exists and it could also be a part of the solution to the FYSP.…”

Volatile (F, Cl, OH) concentrations in lunar apatites and britholites as a measure of lunar magmatic volatile abundances

“…Earth's moon is exceptionally important to human culture and the existence of life on Earth. Heller et al (2021) suggest that the moon's tidal pull produced enough heat to keep the early Earth's surface warm while the sun was not yet at its full radiative strength, and this helped contribute to some stability of the early Earth's climate. It is larger than other moons in our solar system proportional to the size of the planet.…”