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 yet recognised on Earth, and push the record of impacts back by more than two hundred million years. The blow fell as the Palaeoproterozoic ice ages were ending, and if it landed on ice, the steam it blasted into the atmosphere could have hastened the thaw.

Why it matters

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

Dating & uncertainty

Shock-recrystallised monazite gives 2229 ± 5 Ma, and shock-reset zircon agrees. The date falls within uncertainty of the youngest Palaeoproterozoic glacial deposits, which is what makes the climate argument tempting. What has actually been calculated is the water vapour such an impact would release; that it ended a global glaciation has never been shown.

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