Evidence of Ancient Planetary Smash-Up in Australia
May 20, 2016
Dinosaur lovers know that a huge asteroid played a significant role in the ancient animal group’s extinction. An asteroid 65 million years ago led to the extinction of all dinosaurs except birds. But many other asteroids have struck Earth, some of them even larger than the one that ended the dinosaurs’ reign at the end of the Cretaceous. A team of researchers led by Andrew Glikson of the Australian National University has discovered evidence of an impact billions of years ago that was so colossal that it reshaped the very face of the earth. They published their findings in the journal Precambrian Research.
An asteroid is a rocky or metallic object smaller than a planet that orbits a star. Scientists think that asteroids are made up of material left over from the formation of the solar system. Such processes as erosion and volcanic activity have altered the planets and moons. But much of the material in asteroids is almost unchanged. Sometimes, these objects cross paths with Earth. The atmosphere protects the Earth from most asteroid strikes. Air friction will disintegrate an asteroid smaller than about 160 feet (50 meters) in diameter before it can reach the surface. But larger objects can reach Earth, forming impact craters and causing other damage.
Glikson and his team studied sediments in Marble Bar, Western Australia. The region has some of the oldest sediment on Earth. They analyzed small glass beads called spherules and determined that they formed from material vaporized during a huge impact event. They dated the impact to have occurred about 3.5 billion years ago. Other metals consistent with those found in asteroids were also discovered in the sediment. The team estimated that the asteroid measured 12 to 18 miles (20 to 30 kilometers) across. An impact with such an object would have caused earthquakes greater than magnitude 10 on the Richter scale and sent tsunamis hundreds of feet (or meters) high crashing to shore.
This asteroid struck an Earth that was very different from the one we know today. Although such an impact would have wrecked entire ecosystems if it occurred today (or in the time of the dinosaurs), there was very little life to disrupt 3.5 billion years ago. Life probably formed around the same time as the impact and consisted of water-dwelling, single-celled organisms. There was no life on land. Earth also looked nothing like it does today. Since the impact, the actions of plate tectonics have continuously reshaped the planet and destroyed the crater left by the asteroid. Thus, scientists will probably never learn where it struck. But the research done by Glikson and his team will help us better understand the history of the early solar system and the conditions on Earth just as life got its start.