These days we freak out whenever some dinky bollide explodes in the sky over Russia. But scientists have now reconstructed the effects of an enormous 3.26-billion-year-old asteroid impact on Earth that boiled the oceans, turned the sky red hot, and generated a half-hour-long earthquake that shook the planet.
Though we have heard about ancient impacts such as the dinosaur-killing asteroid that hit our planet 65 million years ago, the image above really gives a sense of perspective for these events. To have looked up in the sky and seen a space rock that dwarfed any mountain on Earth would have been chilling. The gigantic object was about 30 miles wide, roughly the width of Rhode Island. It struck an area of what is now South Africa, generating a crater that would have stretched halfway across that country. The energy it released boiled the top layer of the ocean and sent tsunamis hundreds of feet high through the remaining waters.
Researchers know all this from studying fractures in a rock layer in South Africa known as the Barberton greenstone belt, one of the oldest rock formations on Earth. These fissures were created when the asteroid slammed into the ground at more than 42,000 miles per hour. Tectonic processes have since erased most of the scars left behind by this impact but scientists have found sand-sized spherules in the fractures that condensed from a cloud of vaporized created after the asteroid hit. They have also discovered concentrations of iridium, an element that is relatively rare on Earth but more abundant in asteroids.
Using data gleaned from the rock bed, researchers modeled the impact. They conclude that the massive asteroid would have struck an ocean basin thousands of miles from the Barberton greenstone belt, deforming the seafloor, generating seismic waves and tsunamis, and releasing a huge amount of energy. Even as tsunamis continued to rock the area, a rain of spherules would have condensed from the rock vapor of the impact. The event may have even permanently altered the tectonic plates of the early Earth, leading to the modern plates we have today. The findings will appear in the journal Geochemistry, Geophysics, Geosystems.
The impact is a testament to a period in the solar system's history known as the Late Heavy Bombardment, when giant space rocks still roamed around the sun, slamming into the early planets. It is likely that a few dozen asteroids similar in size to the 3.26-billion-year-old one studied here also struck the Earth at the time.
