EARTH

The Largest Body of Magma

~2.06 to 2.055 billion years ago

Proterozoic · Paleoproterozoic · Rhyacian

Beneath present-day South Africa, a million cubic kilometres of magma pushed into the crust, pulse after pulse rather than in a single filling, and cooled there slowly. As it cooled, its minerals settled out in order of density, layer upon layer, like sediment in still water, building a stack seven kilometres thick and a hundred across; the main volume crystallised inside a single million years. A few of those layers hold some of the world's richest seams of platinum, chromium and vanadium.

Why it matters

Much of the platinum in the world's catalytic converters crystallised in this one body of rock, while the air was still learning to hold oxygen.

Dating & uncertainty

Uranium-lead dating of zircon and other accessory minerals puts the whole complex between 2060 and 2055 million years, with the main volume inside a single million-year interval. Those dates argue that it grew as a stack of sills rather than filling as one great tank, though the sampling behind them has been challenged in print, comment and reply.

Sources

1. Scoates et al. (2021), Journal of Petrology · Dating the Bushveld Complex: timing of crystallization, duration of magmatism, and cooling
2. Mitchell et al. (2021), Journal of Petrology · Comment on Dating the Bushveld Complex
3. Scoates et al. (2021), Journal of Petrology · Reply to comment on Dating the Bushveld Complex

Earth history as one day

13:06:3610 h 53 min before midnight

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