Few scars can be found on Earth’s “face” to match Vredefort’s. A good handful of years ago —2 billion, to be precise— a huge asteroid between five and ten kilometers in diameter fell on the southwest of what we now know as Johannesburg, in South Africa, at a devilish speed. The collision was so brutal that displaced a large amount of rock. The result: a huge dent that, once the structure finished collapsing and settled, experts estimate that it reached a width of between 180 and 300 km.
Its tremendous dimensions make Vredefort the largest impact crater on Earth known to date; but it is not, far from it, the only sinkhole that a meteorite has opened when colliding with our planet. Throughout the globe, the Planetary and Space Sciences Center (PASSC), of the University of New Brunswick, in Canada, has detected a good handful. In its online database, [Earth Impact Database](http://www.passc.net/EarthImpactDatabase/New website_05-2018/Index.html) (EID), cita 190 confirmed.
A growing catalog
Researchers continue to hunt for data to understand them better and locate new holes. A decade ago European geologists located in Greenland a crater about a hundred kilometers in diameter caused by an asteroid 3,000 million years ago and in 2019 another team from Oxford shared evidence of a similar finding – 20 kilometers – in the United Kingdom.
The question is, What are impact craters or astroblems? NASA defines them as the result of the impact of an object —asteroid or meteorite, for example— against the surface of another larger solid, such as a planet or a moon. The phenomenon, of course, is by no means exclusive to Earth. What’s more, after decades of space exploration, astronomers now know that they played a key role in the geological processes of the early solar system.
The oldest lunar surface, for example, is full of sinkholes resulting from the intense “bombing” it suffered for billions of years—from 4.6 to about 3.9 years ago, to be precise. Moreover, even the very birth of our satellite could be the result of the brutal impact of Thea, a stellar object, the size of Mars, against the proto-Earth.
Here on Earth, meteorites also played a fundamental role in the primordial atmosphere and hydrosphere and determined life itself on the planet. The episode of mass extinction recorded 65 million years ago, the one that swept away the dinosaurs, is related without going any further with the effects of a huge impact on what we know today as Mexico. As a reminder we have the Chicxulub crater, 180 km in diameter and almost 20 deep, located mainly underwater off the Yucatan Peninsula.
Neither asteroids nor impact craters are, in any case, an exclusive phenomenon of the past. And to show a button: on March 17, 2013, astronomers observed a flash on the Moon. When NASA took images with the Lunar Reconnaissance Orbiter and compared them with those it had taken a year earlier at the same point, it found that a new impact crater about 18 meters in diameter had “sprouted” on the surface of the satellite. The Mars Color Imager (MARCI) also captured a new sinkhole recorded on the red planet in March 2012.
The Earth itself is bombarded every day by more than a hundred tons of dust and particles the size of sand arriving from space and, more or less once a year, – they specify from the US space agency – a car-sized asteroid hits the atmosphere, disintegrating into a spectacular ball of fire that experts call “bolide”.
If the focus is enlarged a little more, things get complicated: about once every 5,000 years an object the size of a football field hits the Earth causing greater damage. To get a slightly more precise view of how exposed the planet is, see this NASA diagram, made with data collected between 1994 and 2013 of small asteroids that hit the Earth’s atmosphere. The image collects the location of the impacts of objects between 1 and 20 meters and identifies them based on whether they fell during the day or at night.
Although weathering and geological processes have been responsible for clear most impact craters, the surface of our planet continues to present surprising sinkholes of different types. For example, on Earth, scientists differentiate between simple structures, up to four kilometers in diameter, with uplifted rim rocks surrounding a bowl-shaped depression; and complex structures, 4 or more kilometers in diameter.
In addition to being valuable sources of data for scientists, over the years some have also become tourist destinations. Almost all the known ones, after all, have been registered since the middle of the last century. Next, We review some of the most surprising.
Located in Arizona (USA), the also known as Meteor Crater was formed 50,000 years ago as a result of the impact of a meteorite that could have been almost 50 meters wide and traveled at an amazing speed of 45,000 kilometers per hour. It stands out, above all, for being the first that scientists identified as the result of an extraterrestrial impact. Its dimensions: about 1.2 kilometers in diameter and 170 meters deep.
The largest known. It was formed when an asteroid hit Earth about 2 billion years ago in an area we now know as South Africa. When it was formed, the crater reached a diameter of 300 km. It also stands out for its age, although it falls short when compared to the 2,400 million years of the Suavjärvi crater, in Russia,
At first glance, it may not be as easy to see as the Vredefort basin, but the Subdury basin in Canada, the result of the impact of an impact recorded 1.8 billion years ago, stands out for its age and dimensions. The original crater is believed to have been at least 200 km wide. Over time, however, and as can be seen in the photo, has been eroding.
Located in India, more specifically in the Deccan Plateau, a huge plain of volcanic basalt rock left by eruptions recorded 65 million years ago, the Lonar crater stands out for its history. After the CJE officer Alexander identified it in 1823, experts believed it to be a volcanic crater. Today, however, the theory is quite different: it is believed to be the result of a meteorite impact between 35,000 and 50,000 years ago. Its diameter is around 1.8 kilometers and it reaches a depth of around 150 meters.
The Pingualuit Crater was identified north of Quebec, Canada, in 1943, during a US Army Air Force flight. However, geologists had to wait until 1950 to examine it and confirm that it is the crater caused by a meteorite around 1.4 million years ago. Thanks to their identification, the experts located another 20 impact structures in the east of the country. Its diameter is 3.4 km and it houses a lake about 267 m deep.
On the island of Saaremaa, about 20 km northwest of Kingisepp (Estonia), in an area of one square kilometer, the so-called Kaali craters are located. The largest of all has a diameter of about 110 meters and a depth of approximately 20 m. The rest, much smaller, move between 12 and 44 meters in diameter. Its dating is still subject to debate, but in general it is placed in a range that is between 2,420 and 8,400 years ago.
Located approximately 200 kilometers from the city of Antofagasta, south of the Salar de Atacama, in Chile, the Monturaqui crater was first identified in the 1960s as being of meteoritic origin, but questions remain about its exact age. We do know its dimensions: 360 meters from North to South and 380 from East to West with a depth of 31 meters.
Manicouagan Reservoir Crater
In Quebec, in the Côte-Nord region, Canada, one of the most surprising impact craters on Earth is located: Manicougan. The structure is in the form of multiple rings about 100 kilometers wide – the interior, 70 km in diameter, stands out – and contains a 70 km annular lake, the Manicougan Reservoir, which surrounds an interior plateau of the island, René-Levasseur . Scientists believe that the crater was caused by the impact of an asteroid five kilometers in diameter, approximately 215.5 million years ago, during the Triassic period.
Crater Red Ridge
In the desert, south of Namibia, the Roter Kamm crater is located, about 2.5 kilometers in diameter and 130 m deep, although it has not been free of the effect of sand. The structure was formed between about four and five million years ago. Not all meteorite “sinkholes” are so inhospitable, however; sometimes they end up being converted into “cradles”. It happened in Bavaria, where Nördlinger Ries is located, a structure generated 15 million years ago and with a diameter of 25 km. In the center stands Nördlingen, a small town. In Spain, about 50 km from Zaragoza, the Azuara structure is also located, in which an origin linked to a meteorite is also noted, and the small town from which it takes its name.
Gosses Bluff Crater
In Australia, about 160 kilometers west of Alice Springs, we find the Gosses Bluff crater, one of the most studied impact structures in the country. Scientists calculate that it is the result of a one kilometer asteroid around 142 million years ago. Its characteristic central ring of hills has a diameter of four and a half kilometers in length.
Images | Aaron_anderer (Flickr), Nasa (1, 2, 3), PASSC, Vesta (Wikpedia), Amitabhkhare (Wikimedia), Anneli Rumm (Flickr), RudiR (Wikimedia), Copernicus Sentinel-2-ESA y Skyscraper (Wikipedia), Dementia (Flickr)