concept

Faint young sun paradox

A deep clash between astronomy and geology. Stellar models show the early Sun was about 30% dimmer than today. With that feeble a star, the young Earth should have frozen solid into a snowball - yet the geological record is unambiguous that there was liquid water, and life, almost as far back as the rocks go. A weaker sun, and no ice. The widely accepted resolution is the carbonate-silicate thermostat: a cold planet accumulates unconsumed volcanic CO₂ until the greenhouse thickens enough to compensate for the faint sun - the thermostat simply runs hot to cover the weak star, then turns itself down as the Sun brightens.