EARTH

The Oldest Crater

~2.229 billion years ago

Proterozoic · Paleoproterozoic · Rhyacian

A crater seventy kilometres wide once opened in what is now Western Australia; erosion has planed it almost flat, and only the shocked crystals in its floor still tell the story. They make it the oldest impact structure that can still be dated. The blow landed on a glaciated continent, and the steam it threw into the stratosphere may have helped melt the ice.

Why it matters

Impacts are usually cast as killers. This one may have ended an ice age instead.

Dating & uncertainty

Shock-recrystallised monazite and zircon give 2229 ± 5 Ma. The date falls within uncertainty of the youngest Palaeoproterozoic glacial deposits, which is what makes the climate argument tempting; that an impact into an ice sheet could have ended a global glaciation has been simulated, never demonstrated.

Sources

1. Erickson et al. (2020), Nature Communications · Precise radiometric age establishes Yarrabubba as Earth's oldest recognised meteorite impact structure
2. Osinski et al. (2022), Earth-Science Reviews · Impact Earth: a review of the terrestrial impact record
3. Allen et al. (2022), Journal of Geophysical Research: Planets · A revision of the formation conditions of the Vredefort crater

Earth history as one day

12:13:0011 h 47 min before midnight

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