CLIMATE × EARTH

The First Global Glaciations

~2.45 to 2.22 billion years ago

Proterozoic · Paleoproterozoic · Siderian

The oxygen pouring out of cyanobacteria is thought to have 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, and in the last of those episodes they may have joined at the equator, closing over the whole planet.

Why it matters

A waste product of photosynthesis may have come close to freezing the planet solid: the first climate catastrophe with a living cause.

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 so is the correlation between the Canadian and South African glacial beds: the order they came in decides which of them the rise of oxygen could have caused.

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