CLIMATE × EARTH
Pongola: the First Ice Age
~2.9 billion years ago
The Pongola glaciation, about 2.9 billion years ago, is the oldest ice age recorded on Earth, known from beds of boulders in South Africa whose stones were scratched by moving ice.
The Pongola glaciation is an ice age known from deposits in South Africa, and the oldest glaciation recorded on Earth. Beds of boulders there, called tillites, contain stones that moving ice scratched and cut into facets. The fine layered mud nearby contains dropstones, single stones released from floating ice. Each dropstone punched through the soft layers of mud as it fell, and no current can imitate this structure. The deposits formed half a billion years before the first global glaciations.
Why it matters
Under a Sun a fifth less luminous than today's, ice is expected, and what is surprising is that ice was so rare. Some mechanism kept the planet temperate. The Pongola deposit is the exception, and researchers can use it to measure that mechanism.
Dating & uncertainty
The evidence is a disordered bed of boulders in the Pongola Supergroup, a series of rock layers. The bed contains stones scratched and planed flat by ice, and stones that fell from floating ice into finely layered mud. Its chemistry shows a weathering, an alteration of the rock, characteristic of glacial debris. All of it comes from a single basin, the depression where the layers accumulated, which is a narrow basis for claiming a global ice age. The extent of the ice remains unknown.
Earth history as one day
08:40:1015 h 20 min before midnight
if Earth’s 4.54 billion years were compressed into a single day