EARTH
The Bushveld Complex
~2.06 to 2.055 billion years ago
Proterozoic · Paleoproterozoic · Rhyacian
The Bushveld Complex, beneath South Africa, is the largest known body of intrusive magma, a million cubic kilometres of molten rock that entered the crust and cooled there about 2.06 billion years ago.
The Bushveld Complex is a mass of layered rock beneath present-day South Africa, seven kilometres thick and a hundred kilometres across. It formed from a million cubic kilometres of melt, meaning molten rock, that entered the crust and cooled there slowly. It is the largest known body of intrusive magma, magma that solidifies inside the crust. The melt arrived pulse after pulse rather than in a single filling. As the melt cooled, each mineral crystallised at its own temperature and then settled according to its density. This process, fractional crystallisation, built the mass of rock in layers, as sediment settles in still water. The main volume crystallised within a single million years. A few of the layers contain some of the world's richest seams of platinum, chromium and vanadium.
Why it matters
A large share of the platinum used in catalytic converters, the devices that clean car exhaust, comes from the Bushveld Complex. This platinum crystallised in a single body of rock, at the time when the atmosphere was beginning to retain oxygen.
Dating & uncertainty
Scoates and colleagues (2021) used uranium-lead dating, which measures the decay of uranium into lead. They applied it to zircon and other accessory minerals, minerals present in small amounts in the rock. The ages place the whole complex between 2,060 and 2,055 million years ago, and most of its volume within a single million years. They indicate construction by the stacking of sills, sheets of magma injected between rock layers, rather than the filling of a single chamber. Mitchell and colleagues (2021) contested the sampling behind these ages, and Scoates and colleagues replied.
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