CLIMATE × EARTH

The First Global Glaciations

~2.45 to 2.22 billion years ago

Proterozoic · Paleoproterozoic · Siderian

The oxygen pouring out of cyanobacteria destroyed the methane greenhouse that had kept the young Earth warm under a fainter Sun: methane cannot survive in air that contains oxygen, and as it vanished, the planet lost its blanket. Four times in two hundred million years the ice sheets spread; in the last of these episodes they may have joined at the equator, closing over the whole planet.

Why it matters

This was the first great climate catastrophe caused by life itself: a waste product of photosynthesis nearly froze the planet solid.

Dating & uncertainty

Four glacial episodes are dated between 2.45 and 2.22 Ga. Whether the last of them, the Makganyene event, froze the planet to the equator is still argued, and the link to rising oxygen depends on which glaciation came first.

Sources

1. Kopp et al. (2005), PNAS · The Paleoproterozoic snowball Earth: a climate disaster triggered by the evolution of oxygenic photosynthesis
2. Warke et al. (2020), PNAS · The Great Oxidation Event preceded a Paleoproterozoic snowball Earth
3. Rasmussen et al. (2013), Earth and Planetary Science Letters · Correlation of Paleoproterozoic glaciations based on U-Pb zircon ages for tuff beds in the Transvaal and Huronian Supergroups

Earth history as one day

11:18:4512 h 41 min before midnight

if Earth’s 4.54 billion years were compressed into a single day