Alternatives
A minority view, propounded by the Israeli-American physicist Nir Shaviv, uses climatological influences of solar wind, combined with a hypothesis of Danish physicist Henrik Svensmark for a cooling effect of cosmic rays, to explain the paradox. According to Shaviv, the early Sun had emitted a stronger solar wind that produced a protective effect against cosmic rays. In that early age, a moderate greenhouse effect comparable to today's would have been sufficient to explain an ice-free Earth. Evidence for a more active early Sun has been found in meteorites.
The temperature minimum around 2.4 billion years goes along with a cosmic ray flux modulation by a variable star formation rate in the Milky Way Galaxy. The reduced solar impact later results into a stronger impact of cosmic ray flux (CRF), which is hypothesized to lead to a relationship with climatological variations.
An alternative model of solar evolution may explain the faint young Sun paradox. In this model, the early Sun underwent an extended period of higher solar wind output. This caused a mass loss from the Sun on the order of 5−10% over its lifetime, resulting in a more consistent level of solar luminosity (as the early Sun had more mass, resulting in more energy output than was predicted). In order to explain the warm conditions in the Archean era, this mass loss must have occurred over an interval of about one billion years. However, records of ion implantation from meteorites and lunar samples show that the elevated rate of solar wind flux only lasted for a period of 0.1 billion years. Observations of the young Sun-like star π1 Ursae Majoris matches this rate of decline in the stellar wind output, suggesting that a higher mass loss rate can not by itself resolve the paradox.
Examination of Archaean sediments appears inconsistent with the hypothesis of high greenhouse concentrations. Instead, the moderate temperature range may be explained by a lower surface albedo brought about by less continental area and the "lack of biologically induced cloud condensation nuclei". This would have led to increased absorption of solar energy, thereby compensating for the lower solar output.
Read more about this topic: Faint Young Sun Paradox
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