Scientists have known for a long time that the first several billion years of Earth’s existence was a harsh and turbulent time for our planet. Now, Stanford University’s Donald Lowe has released research showing that bad times lasted longer than we previously realized:
Lowe and his colleagues have spent 40 years studying a patch of ancient rocks in eastern South Africa called the Barberton Belt. Over 25 years ago they found four layers of spherical particles, which seemed to have condensed from clouds of vaporised rock. Lowe says they are the traces of four major meteorite impacts, and date from between 3.5 and 3.2 billion years ago.
Now Lowe’s team have described another four layers of spherules from the same period. That means there were eight major impacts within about 250 million years, bolstering the case that the bombardment was still going on.
For its first 1.5 billion years, asteroids exponentially bigger than the one that killed the dinosaurs were regularly hitting the Earth’s surface. Based on the layers of sediment created by these explosions, scientists estimate that the asteroids could have been up to 44 miles wide. The impacts would have caused “earthquake[s] that went on for many minutes and tsunamis that could have circled the entire planet.” Gnarly.
Life already existed on Earth at the time of these upheavals, but because it was microscopic, it’s unlikely that the space rocks caused mass extinctions. They could, however, have killed photosynthetic bacteria living near the ocean’s surface, which could explain why it took so long for the planet to create an oxygen-based atmosphere, a byproduct of photosynthesis. (Photo: Wikipedia)