The destructive space rock was somewhere between 12.4 and 15.5 miles wide.
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The Vredefort crater was birthed 2 billion years ago when
the largest asteroid ever to hit Earth impacted the planet. A new study
suggests the gargantuan space rock was even bigger than previously predicted.
(Image credit: Lauren Dauphin/NASA Earth Observatory/Landsat) |
The largest asteroid ever to hit Earth, which slammed into
the planet around 2 billion years ago, may have been even more massive than
scientists previously thought. Based on the size of the Vredefort crater, the
enormous impact scar left by the gargantuan space rock in what is now South
Africa, researchers recently estimated that the epic impactor could have been
around twice as wide as the asteroid that wiped out the nonavian dinosaurs.
The Vredefort crater, which is located around 75 miles (120
kilometers) southwest of Johannesburg, currently measures about 99 miles (159
km) in diameter, making it the biggest visible crater on Earth. However, it is
smaller than the Chicxulub crater buried under Mexico's Yucatán Peninsula,
which measures around 112 miles (180 km) in diameter and was left by the
dinosaur-killing asteroid that struck Earth at the end of the Cretaceous period
about 66 million years ago.
But impact craters slowly erode over time, which makes them
shrink. The most recent estimates suggest that the Vredefort crater was
originally 155 to 174 miles (250 to 280 km) across when it was formed 2 billion
years ago. As a result, the Vredefort crater is considered the largest impact
crater on Earth despite being smaller than the Chicxulub crater today.
In the past, scientists thought the Vredefort crater was
originally much smaller — around 107 miles (172 km) wide. Based on that
estimate, researchers previously calculated that the asteroid responsible for
the impact would have measured around 9.3 miles (15 km) across and collided at
a speed of around 33,500 mph (53,900 km/h). But in a new study, scientists have
revisited the crater's measurements and gained new insight into the size of the
enormous space rock.
In the study, which was published online Aug. 8 in the
Journal of Geophysical Research: Planets, researchers
recalculated the size of the Vredefort asteroid and found that the destructive
space rock likely measured somewhere between 12.4 and 15.5 miles (20 and 25 km)
across, and could have been traveling between 45,000 and 56,000 mph (72,000 and
90,000 km/h) when it struck our planet.
"Understanding the largest impact structure that we
have on Earth is critical" because it allows researchers to build more
accurate geological models, study lead author Natalie Allen, a doctoral
candidate in the Johns Hopkins University Department of Physics and Astronomy
in Baltimore, said in a statement. More accurate predictions
of impactor sizes also could shed light on other craters on Earth and
throughout the solar system, she added.
Size uncertainty
In the past, scientists have struggled to pin down the
original size of the Vredefort crater due to its erosion over the past 2
billion years.
To understand how erosion affects ancient impact craters
such as Vredefort, imagine continually slicing the rim off a bowl, Roger
Gibson, a structural geologist at University of the Witwatersrand in South
Africa who was not involved in the study, told NASA's Earth Observatory
In addition to the natural erosion of the Vredefort impact structure, newer rock formations have emerged atop parts of the crater, the researchers wrote. As a result, most of the crater's original structure has been completely covered by younger rocks and only small sections of the crater's elevated rim are visible today, making it even harder to tell how big the crater used to be.
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Today, large parts of the Vredefort crater are barely
recognizable as an impact structure. (Image credit: Shutterstock) |
However, other recent studies have estimated the Vredefort
crater's size by focusing on minerals surrounding the crater. By doing this,
scientists have spotted deformations and shock fractures in crystals, like
quartz and zircon, that were caused by the ancient impact and thereby expand
the known radius of the blast, the study authors wrote.
As a result, the researchers are confident that their new estimate for the size of the Vredefort asteroid is more accurate than previous estimates.
A cataclysmic impact
When the dinosaur-killing asteroid, which likely measured
around 7.5 miles (12 km) wide, hit Earth around 66 million years ago, the
destruction caused by the impact was immense. The Cretaceous-ending event
caused widespread forest fires and acid rain; generated mile-high waves in a
tsunami that reached halfway across the planet; and sent plumes of ash and dust
into the atmosphere, drastically altering the climate. Around 75% of life on
Earth was wiped out by the event, according to a study published in December
2021 in the journal Scientific Reports.
Based on the revised calculations of the Vredefort crater's
original size, the new study suggests that the Vredefort asteroid was likely
around twice as large as the dinosaur-killer. It also may have been traveling
much faster, so its impact would have been even more severe — potentially the
single largest energy-release event in Earth's history, the study authors
reported. However, because the impact happened so long ago, there is scant
evidence of the blast's ground-shaking power and the effects of the collision
on the planet.
"Unlike the Chicxulub impact, the Vredefort impact did
not leave a record of mass extinction or forest fires given that there were
only single-cell lifeforms and no trees existed two billion years ago,"
study co-author Miki Nakajima, a planetary scientist at the University of
Rochester in New York, said in the statement. "However, the impact would
have affected the global climate potentially more extensively than the
Chicxulub impact did."
Therefore, continuing to study Vredefort crater could be the
only way researchers learn more about this cataclysmic impact.