Why so few craters on Earth compared with the moon?
Manicouagan Crater in Quebec, Canada. Public domain NASA photo.
It’s well-known that the surface of the moon is covered with many thousands of impact craters. However, Earth appears to not have nearly as many. The reason for this is that the Earth’s weather and tectonic forces make most craters eventually disappear. Also, Earth’s surface is 71% water, and so many meteors, asteroids, or comets that have hit the Earth, have splashed into the ocean somewhere.
In total, there are 170 (approximately) known impact craters on Earth’s surface. A few of the very best ones, if you want to see one, are Meteor Crater in Arizona (in the photo below), Wolfe Creek Crater in Australia, Amguid Crater in Algeria, and Monturaqui Crater in South America – although there are many other good ones around the world.
Earth’s largest impact craters
Manicouagan Lake in Quebec, Canada (in the photo above) is a huge meteorite crater formed 214 million years ago, and measures 40 miles (70 km) in diameter. It is clearly visible from space.
In northern Russia is Kara Crater, which is 70 million years old and measures 73 miles (120 km) in diameter.
The crater which caused or at least heavily contributed to the end of the reign of the dinosaurs 65.5 million years ago, formed by an asteroid or comet estimated to be six miles (10 km) in diameter, is located on the Yucatan Peninsula in Mexico. This massive crater, called Chicxulub Crater, is 110 miles (180 km) across.
Two craters are known to exist that are larger than Chicxulub. One in South Africa is 2.0 billion years old and 300 km (185 miles) in diameter. Another in Ontario, Canada is 1.85 billion years old and 250km (155 miles) in diameter. When these impact events occurred, some simple organisms existed, but some more complex organisms such as algae and fungi had not yet evolved. The first plants and animals were still over a billion years away.
A massive asteroid strike could happen again
As far as is known, the object that struck the Earth 65.5 million years ago, causing all dinosaurs to go extinct with the exception of avian dinosaurs (birds), plus the extinction of pterosaurs, mosasaurs, plesiosaurs, ammonites, and many other species of animal and also plant life, was the largest since the event that occurred in what is now Canada 1.85 billion years ago. And it’s true – objects as large or larger can strike the Earth again someday.
NASA and other agencies and organizations around the world track the largest known asteroids and comets. At this time none are known to be on a path that will collide with Earth in the next century. But not every asteroid or comet is known, either. (For more info, see the NASA website.)
Beautiful Meteor Crater (also called Barringer Crater) in Arizona, USA
Video of the asteroid that exploded over Chelyabinsk, Russia in February 2013
This is the only asteroid known to have injured humans. The injuries occurred when this asteroid exploded over the large Russian city of Chelyabinsk, causing a massive bright fireball. Curious city-dwellers went to their windows to see what happened, and then the shockwaves arrived (sound waves travel slower than light) and shattered many thousands of windows across the city.
Prior to entering Earth’s atmosphere, this asteroid was about 59 feet (18 meters) in diameter, and weighed about 10,000 tons (9,100 tonnes). When it exploded, it released the approximate energy of a magnitude 7.0 earthquake on the Richter scale (equivalent to about 30 times as much energy released by the atomic bomb dropped on Hiroshima, Japan during World War II).
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