Earth's first ice age

The Pongola glaciation, recorded in the Mozaan Group of South Africa, is the oldest known glacial episode. Diamictites, dropstones and triple oxygen isotope data together show genuine ice at low latitude rather than merely cool conditions. That a planet warmed by a thick carbon dioxide greenhouse, under a Sun 25% dimmer than today's, could still glaciate suggests the early climate was less stable than the faint young Sun problem implies — and possibly that rising oxygen was already eating away the methane keeping it warm.