Meteorite impacts on Earth are not uncommon.event. This happened even in our memory - on February 15, 2013, a meteorite burst into the atmosphere, the fragments of which fell in the vicinity of Chelyabinsk. And at the beginning of the last century, the Tunguska meteorite fell, which was 10 times larger than the Chelyabinsk meteorite. But what was the largest asteroid ever to hit Earth? In general, the largest celestial body that crashed into the Earth is Theia, but this is the planet that caused the formation of the Moon. But this is a planet, and we are talking about asteroids. For a long time it was believed that this is the space rock that killed the dinosaurs, and left the Chicxulub crater after hitting the Earth. But, as it recently turned out, this is not so - the first place in size belongs to the celestial body that left the Vredefort crater after the fall. We offer to learn more about what kind of asteroid it was.
The largest crater on earth
The largest asteroid that crashed into our planetunlike what killed the dinosaurs, did not lead to mass extinction. Fortunately, the event happened long before the appearance of vertebrates - about two billion years ago. It crashed into a patch of Earth where South Africa is now located. The Vredefort crater is located 120 km southwest of Johannesburg (the largest city in South Africa). Its diameter is about 160 km. Therefore, Vredefort is considered the largest crater on our planet.
This will surely surprise many, because the Chicxulub crater180 km in diameter. Why such strange arithmetic? The thing is that the Chicxulub crater arose 66 million years ago. That is, the difference in time between the falls of two asteroids exceeds one billion years. At the same time, it is known that craters collapse and narrow over time.
Previously, scientists assumed that the size of the craterVredefort was originally about 172 km in diameter, that is, it was still smaller than Chicxulub. According to these dimensions, scientists assumed that the asteroid itself was about 15 km in diameter. Its flight speed at the time of the collision was 53,900 km/h. However, in a recent study published in the Journal of Geophysical Research: Planets, the authors of the work concluded that the size of the asteroid was actually much larger.
According to their estimates, the diameter of the Vredefort 2 craterbillion years ago was in the range from 250 to 280 km. That is why it was called the largest impact crater on Earth, despite the fact that in fact its dimensions are not the largest.
The dimensions of the largest asteroid that fell to Earth
After recalculating the size of the asteroid, it turned out thatit was 20 to 25 km in diameter. Its speed at the moment of collision with our planet was from 72,000 to 90,000 km/h. But why do scientists need to know what the asteroid and crater was like 2 billion years ago? According to the researchers themselves, accurate size predictions will help shed light on other craters, not only on our own, but also on other planets of the solar system. But that's not all - detailed information about the meteorite will allow us to build more accurate geological models.
But why did the scientists get it wrong in the first place?misjudged the size of the crater? It has long been known that the diameter of craters decreases with time. This process can be compared to a cone whose upper part is gradually cut off. After each cut, the diameter will become smaller and smaller.
However, the diameter of the Vredefort crater is not influenced byonly erosion. Rocks formed on its tops. That is, the original structures were not preserved, they are hidden under newer rocks. Therefore, it is impossible to accurately estimate what the diameter of the crater was by simply measuring it.
However, the researchers in their studyotherwise, they focused their attention on the minerals that surround the crater. They carefully studied the deformations and impact cracks in crystals (quartz and zircon). This made it possible to estimate the diameter of the crater by indirect signs.
Obviously, if this asteroid fell later, itwould lead to even more disastrous consequences for life than the fall of the asteroid that killed the dinosaurs. Although the fall of the Chicxulub meteorite. was also a catastrophe of colossal proportions, which led to a two-year nuclear winter. But two billion years ago, only single-celled organisms existed on Earth. Therefore, neither forest fires nor the extinction of animals occurred.