Key Takeaways:

  1. The Vredefort crater in South Africa might be the largest impact crater on Earth, even bigger than the dinosaur-killing Chicxulub crater, after accounting for erosion.
  2. New estimates suggest the Vredefort impactor was significantly larger (12.4-15.5 miles) and faster (45,000-56,000 mph) than previously thought.
  3. Determining the Vredefort crater’s original size is challenging due to 2 billion years of erosion and younger rock formations covering parts of it.
  4. The Vredefort impact might have been the most powerful in Earth’s history, but due to the time period, there’s no record of mass extinction or environmental changes like with the Chicxulub impact.
  5. Continued research on the Vredefort crater can reveal more about this ancient, catastrophic event.

It’s possible that the largest asteroid to ever strike Earth was even more massive than previously believed. It collided with the planet approximately 2 billion years ago. Researchers recently estimated that the epic impactor may have been around twice as wide as the asteroid that wiped out the nonavian dinosaurs based on the size of the massive impact scar left by the massive space rock in what is now South Africa, known as the Vredefort crater.

The largest visible crater on Earth is the Vredefort crater, which is situated approximately 75 miles (120 km) southwest of Johannesburg and has a diameter of approximately 99 miles (159 km). It is smaller, though, than the Chicxulub crater, which is located beneath the Yucatán Peninsula in Mexico. Chicxulub is approximately 112 miles (180 km) in diameter and was created by an asteroid that killed dinosaurs when it struck Earth 66 million years ago at the end of the Cretaceous period.

However, impact craters gradually get smaller due to erosion. According to the most recent estimates, when the Vredefort crater formed two billion years ago, it was originally between 155 and 174 miles (250 and 280 km) across. Because of this, even though the Vredefort crater is smaller than the Chicxulub crater today, it is still regarded as the largest impact crater on Earth.

The Vredefort crater was once believed by scientists to have been considerably smaller, measuring about 107 miles (172 km) in width. According to that estimate, scientists previously determined that the impact-causing asteroid would have been about 9.3 miles (15 km) across and would have collided at a speed of about 33,500 mph (53,900 km/h). However, scientists revisited the crater’s measurements and discovered new information about the size of the massive space rock in a recent study.

Researchers recalculated the size of the Vredefort asteroid and discovered that it likely measured between 12.4 and 15.5 miles (20 and 25 km) across. It may have been traveling between 45,000 and 56,000 mph (72,000 and 90,000 km/h) when it struck our planet. The study was published online in the Journal of Geophysical Research: Planets.

Lead author of the study Natalie Allen, a doctoral candidate in the Department of Physics and Astronomy at Johns Hopkins University in Baltimore, said in a statement that “understanding the largest impact structure that we have on Earth is critical” because it enables scientists to create more accurate geological models. She went on to say that more precise estimates of impactor sizes might provide information about other craters on Earth and in the solar system.

Uncertainty about size

The erosion of the Vredefort crater over the last two billion years has made it difficult for scientists to determine the crater’s original size in the past.

In 2018, Roger Gibson, a structural geologist from the University of the Witwatersrand in South Africa who was not involved in the study, explained to NASA’s Earth Observatory how erosion affects ancient impact craters like Vredefort. He described it as like continually slicing the rim off a bowl. “If you slice horizontally through the bowl progressively, you would see that the bowl’s diameter will decrease with each slice you take off.”

The researchers noted that newer rock formations have emerged atop parts of the crater in addition to the natural erosion of the Vredefort impact structure. Because of this, the majority of the crater’s original structure has been entirely covered by younger rocks, and only a small portion of the elevated rim of the crater is visible today, making it even more difficult to determine the crater’s original size.

Today, large parts of the Vredefort crater are barely recognizable as an impact structure. (Image credit: Shutterstock)

However, by concentrating on the minerals surrounding the crater, other recent studies have estimated the size of the Vredefort crater. According to the study’s authors, by doing this, researchers have discovered shock fractures and deformations in crystals like quartz and zircon that were brought on by the ancient impact, extending the blast’s known radius.

Because of this, the scientists are certain that their updated estimates of the Vredefort asteroid’s size is more accurate than earlier ones.

The impact that killed the dinosaurs occurred 66 million years ago, and the asteroid that killed them probably had a width of 7.5 miles (12 km). The end of the Cretaceous period produced massive forest fires, acid rain, a tsunami halfway around the world, and miles-high waves. It also sent dust and ash plumes into the atmosphere, which significantly changed the planet’s climate. The event eliminated about 75% of life on Earth, according to a study that was published in the journal Scientific Reports.

The new study indicates that the Vredefort asteroid was probably about twice as large as the dinosaur-killer, based on the updated estimates of the crater’s original size. The impact would have been even more severe because it might have been traveling much faster; in fact, the study’s authors speculate that it might have been the single largest energy-release event in Earth history. Nevertheless, there is little proof of the blast’s earth-shaking force or the collision’s effects on the planet because it occurred so long ago.

The statement from study co-author Miki Nakajima, a planetary scientist at the University of Rochester in New York, said “since there were only single-cell lifeforms and no trees existed two billion years ago, the Vredefort impact did not leave a record of mass extinction or forest fires, unlike the Chicxulub impact.” “However, the impact would have affected the global climate potentially more extensively than the Chicxulub impact did.”

Thus, the only way scientists may be able to learn more about this catastrophic impact is if they keep studying the Vredefort crater.

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