The faint young Sun problem

Abstract

[1] For more than four decades, scientists have been trying to find an answer to one of the most fundamental questions in paleoclimatology, the "faint young Sun problem." For the early Earth, models of stellar evolution predict a solar energy input to the climate system that is about 25% lower than today. This would result in a completely frozen world over the first 2 billion years in the history of our planet if all other parameters controlling Earth's climate had been the same. Yet there is ample evidence for the presence of liquid surface water and even life in the Archean (3.8 to 2.5 billion years before present), so some effect (or effects) must have been compensating for the faint young Sun. A wide range of possible solutions have been suggested and explored during the last four decades, with most studies focusing on higher concentrations of atmospheric greenhouse gases like carbon dioxide, methane, or ammonia. All of these solutions present considerable difficulties, however, so the faint young Sun problem cannot be regarded as solved. Here I review research on the subject, including the latest suggestions for solutions of the faint young Sun problem and recent geochemical constraints on the composition of Earth's early atmosphere. Furthermore, I will outline the most promising directions for future research. In particular I would argue that both improved geochemical constraints on the state of the Archean climate system and numerical experiments with state-of-the-art climate models are required to finally assess what kept the oceans on the Archean Earth from freezing over completely.

Mass-loss Rates from Coronal Mass Ejections: A Predictive Theoretical Model for Solar-type Stars

“…Drake et al (2013) also suggested that CME mass loss may help explain the so-called "faint young Sun problem," in which the young Earth appears to have had liquid water even though the Sun's luminosity would have implied global temperatures below the freezing point (Sagan & Mullen 1972;Feulner 2012). One possible solution to the problem is that the young Sun may have been more massive (and thus more luminous) than standard solar models predict.…”

Organic Aerosols in the Presence of CO2 in the Early Earth and Exoplanets: UV–Vis Refractive Indices of Oxidized Tholins

“…On Earth, substantial evidence points that life came into existence either near the end of the Hadean Eon (4.6 -4 Myr) or early in the Archean Eon (4 -2.5 Myr) releasing oxygen into the atmosphere (Kasting 1993). The atmosphere of the early Earth was N 2 dominated and models show that it could have included up to 3 -10 % of CO 2 as well as CH 4 (Feulner 2012;von Paris et al 2008). CO 2 is considered to be the dominant greenhouse gas offsetting the early Sun that could have kept the early Earth unfrozen, but it could also be removed from the atmosphere by the flow of carbon into the mantle (Sleep & Zahnle 2001).…”

Hydrogen-Nitrogen Greenhouse Warming in Earth's Early Atmosphere

“…Increased atmospheric carbon dioxide is one plausible solution because of the climate buffer provided by the crustal carbonate-silicate cycle (8), but efficient mantle CO 2 cycling in the Hadean and Archean probably reduced the strength of this feedback (9). Interpretation of the geological record is difficult, but analyses of mid to late Archean paleosols suggest between around 10 and 50 times the present atmospheric pressure (PAL) of CO 2 (7,10). Even lower values (around 3 × PAL) have been derived from analysis of magnetite and siderite equilibria in Archean banded iron formations, although the underlying assumptions behind these limits have been questioned (5, 7).…”

“…However, all of these mechanisms have subsequently been shown to suffer important defects (6,7). Increased atmospheric carbon dioxide is one plausible solution because of the climate buffer provided by the crustal carbonate-silicate cycle (8), but efficient mantle CO 2 cycling in the Hadean and Archean probably reduced the strength of this feedback (9).…”