The S2 impact, Barberton
A rock far bigger than the dinosaur-killer, which may have briefly fed early life.
Key facts
- When
- about 3.26 billion years ago
- Where
- Barberton Greenstone Belt, Mpumalanga, South Africa
- What hit
- an asteroid perhaps 40 to 60 km across
- Era
- Deep time
- Location
- 25.80° S, 31.00° E
Estimated at 50 to 200 times the mass of the Chicxulub impactor, so the energy was of the order of billions of megatons of TNT.
Enough to boil the top layer of the oceans worldwide and darken the sky for years.
What happened
Some of the oldest rocks on Earth, in the Barberton Mountains of north-east South Africa, hold thin layers made of tiny glassy beads called spherules. Each layer is the fallout of a giant impact: rock vaporised by the blast condensed in the sky into droplets that rained down across the planet. At least eight such layers are known from between about 3.5 and 3.2 billion years ago.
The layer called S2 is one of the best preserved. From the amount of meteoritic material it contains, scientists estimate the impactor was tens of kilometres across. Its crater has long since disappeared, destroyed by more than three billion years of geological change.
At the time, Earth had no land plants or animals. Life was microbial, and the oceans contained little oxygen.
Effects
The impact would have sent a tsunami sweeping round the world that churned the sea floor, boiled the surface layer of the ocean, and filled the air with dust and soot that shut out sunlight. Research published in 2024 found something unexpected: once the dust settled, the layers show signs of a boom in microbes. The tsunami mixed iron-rich deep water up to the surface, and the asteroid itself delivered phosphorus, a nutrient that was scarce, so iron-loving microbes flourished.
The evidence
Spherule beds traced over large areas, with high levels of iridium and chromium isotopes that match meteorites rather than Earth rock, plus layers of jumbled rock torn up by giant waves directly above them.
Did you know?
Giant impacts like S2 were probably far more common in the first billion years of Earth's history than at any time since.
Similar spherule beds of the same age are found in the Pilbara of Western Australia, and some may record the same impacts.
Related pages
How is impact energy measured? See energy explained, or try the impact calculator.