Not every space rock that enters Earth’s atmosphere makes it to the ground, and most of the rocks that do penetrate our planet’s atmosphere aren’t colossal. According to NASA, they’re quite small, measuring about 1 meter in width. This is fortunate for Earth because any space rock with a diameter below 25 meters usually won’t make it through the atmosphere. The high speed of space rocks heats up the gases in the atmosphere, causing the rock to burn up (technically, it becomes a meteor when it encounters the atmosphere). In most cases, any space rock debris that does make it through the atmosphere causes little to no damage upon impact with the ground.
For instance, a 17-meter-wide asteroid exploded over Chelyabinsk, Russia, in 2013, creating a shockwave that shattered windows and caused injuries. However, it didn’t create an impact crater, as the asteroid didn’t actually touch the ground, as reported by Live Science previously. Gerhard Drolshagen, a physicist specializing in near-Earth objects at the University of Oldenburg (Germany), noted that most of it vaporized into dust and smaller meteoroids during its flight. A 1.5-meter-wide asteroid at the bottom of a nearby lake, along with some smaller fragments, was all that remained, according to a report from the 45th Lunar and Planetary Science Conference in 2014.
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Image: AFP
However, the 190 known impact craters on Earth demonstrate that a few larger asteroids did manage to penetrate, although they remain relatively few. Among these craters, 44 have diameters of 20 kilometers or larger. Here’s what we know about the three largest impact craters:
Firstly, the Vredefort crater in South Africa is the largest known impact crater on Earth. The original crater was estimated to be around 300 kilometers in diameter but has eroded and is thought to have formed about 2 billion years ago, according to NASA’s Earth Observatory. Based on the remaining rim, scientists estimate the impacting asteroid to have been 10-15 kilometers in diameter.
An object larger than 1 kilometer in size could cause global effects. Therefore, the asteroid that created the Vredefort crater delivered a catastrophic blow, potentially equivalent to the event that wiped out the dinosaurs. The impact may have caused worldwide wildfires and a substantial amount of debris launched into the atmosphere, altering the climate for many months to years.
Secondly, the Chicxulub crater on Mexico’s Yucatan Peninsula is 180 kilometers wide and much younger than Vredefort. An asteroid about 12 kilometers in diameter created it 66 million years ago. Although the volcano now partially sits on land, Yucatan was under shallow seas during the impact. The collision resulted in the extinction of 75% of species, including non-avian dinosaurs.
The impact may have propelled debris into space. Upon reentry to Earth, the flaming debris would have set ablaze much of the planet’s surface. The impact also produced a dust cloud that covered the Earth for years, blocking sunlight and disrupting the food chain. The non-avian dinosaurs that survived the initial impact may have ultimately succumbed to starvation.
Thirdly, the Sudbury Basin in Ontario, Canada, ranks as the third-largest crater in terms of size and, like Vredefort, is one of Earth’s oldest known impact craters. A 2014 study in the journal Terra Nova suggests it might not have been an asteroid but a massive comet or a rock formed from fragments of an asteroid and ice. With diameters ranging from 9.6 to 14.5 kilometers, the cosmic object struck Earth around 1.8 billion years ago. Due to erosion, identifying this impact crater is currently challenging.
Of the 44 largest impact craters formed by space rock collisions on Earth, 39 were created over 10 million years ago. The Kara-Kul crater in Tajikistan formed less than 5 million years ago.
Without oceans and erosion, Earth’s surface would resemble that of the Moon, dominated by volcanic features. This suggests that more asteroid impacts and possibly larger impacts could have occurred, beyond our current knowledge.