EARTH

The Gold Came Late

~4.4 billion years ago

Hadean

Gold and platinum dissolve eagerly in molten iron. So when the iron drained to the centre to form the core, it should have taken every last gram down with it, leaving the rock above stripped bare. That rock holds far too much. The usual explanation is a late delivery: a final rain of asteroids, a fraction of one per cent of the planet's mass, falling after the core had closed for good.

Why it matters

Every gram of gold ever mined came out of rock that ought to hold none. It reached the Earth late, possibly in the same final rain that, some argue, delivered the water.

Dating & uncertaintyDisputed

The accounting has lately grown harder, not easier. New modelling finds that the metal of any impactor bigger than about a kilometre sinks through to the core, leaving no trace in the mantle, which is precisely where the excess is measured. For the books to balance, either the incoming metal shattered into dust fine enough to stay suspended in the rock, or the late rain was made of oxidised, metal-poor bodies. The simple version of the story no longer adds up on its own.

Sources

1. Li (2022), Acta Geochimica · Late veneer and the origins of volatiles of Earth
2. Anslow et al. (2026), Journal of Geophysical Research: Planets · The efficient delivery of highly siderophile elements to the core creates a mass accretion catastrophe for the Earth
3. Halliday & Canup (2022), Nature Reviews Earth & Environment · The accretion of planet Earth

Earth history as one day

00:44:2423 h 16 min before midnight

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