Roughly 3.3 billion years ago, Earth's early life forms were plunged into an unimaginable hell, when a series of massive asteroids smashed into the young planet, vaporising the oceans and scorching the skies.
Image: Johan Swanepoel/Shutterstock
We've heard about one of these asteroids before — a 58 kilometre-across object that, upon impact 3.26 billion years ago, shook the entire planet for a half hour. Now, geologist Don Lowe of Stanford University presents us with two other 50 to 100 kilometer-across impactors from the same time period. Each of these asteroid collisions would have boiled Earth's oceans, reducing global sea levels by up to 100 metres. As Lowe told Science News, the cataclysmic events probably had a dramatic impact on the early evolution of life:
"These impacts would have a profound influence on any life trying to evolve into more complex, low-temperature organisms. They'd keep getting whacked by these giant impactors and driven to extinction or near extinction."
The new findings come from studying a geologic formation in South Africa known as the Barberton greenstone belt. Within this belt are 8 distinct layers that chronicle asteroid impacts occurring some 3.5 to 3.2 billion years ago. The two layers discussed in the current study are filled with tiny silica pellets, which the geologists interpret as indicators of molten rock rainstorms that took place after asteroids fried the Earth's surface.
Exactly how much of the world's ocean volume evaporated can only be roughly estimated from the geologic record, but based on earlier modelling work, the surface oceans probably boiled for over a year. It's amazing that anything at all managed to survive, but then, microbes always do seem to miraculously find a way. [Science News]