Jakarta –
About two billion years ago, a asteroid fell near present-day Johannesburg the largest crater in the world currently known.
Initially, the impact caused the Earth’s surface to crack 60 miles wide, but the crater grew to three times wider as its walls collapsed and the rocks beneath it began to bounce. Scientists say the impact was bigger and more energetic than the asteroid impact that killed the dinosaurs.
At the moment, Vredefort crater, the name of the crater, did not look like a bowl at the time of its formation and was certainly not the site of a global catastrophe. Severe erosion leaves only part of the ring still visible. Some parts of the crater even include agricultural land. Being able to find that much evidence from this crater is a stroke of luck, scientists say.
A new study finds that Earth’s oldest craters, which could hold clues to how life survived on our early planet, are disappearing and there’s not much we can do about it. The study estimates that due to natural erosion, craters more than 2 billion years old may be indistinguishable from other non-crater rocks.
Take an example Vredefort crater. If the impact event had occurred 200 million years earlier, then erosion processes would have obliterated the crater by now, according to new research. To scientists today, it appears that the asteroid never hit.
“It’s not that Vredefort has disappeared. All his ‘cousins’ have disappeared,” said Matthew S. Huber, the study’s lead author. “It’s a coincidence that we have this amount of evidence about Vredefort in our possession,” he said as quoted by the Washington Post.
A 2 billion year old crater may sound ancient, but it represents only half of Earth’s history. Craters have occurred since the beginning of the Solar System, appearing on the surfaces of many rocky bodies. Geologists have counted about 200 impact craters on Earth’s surface, with the oldest dating back about 2 billion years. But Huber said there should be more.
“We recognize that events with huge impact are bound to happen because we have products shaped by them,” Huber said. “Any building that once existed will be eroded. If we can’t find it, then the building effectively doesn’t exist,” he said.
Trying to Unravel the Mystery
Huber and his colleagues wanted to know when erosion caused a crater to stop being a crater. To answer this question, the researchers dug Vredefort crater 190 miles wide. At the moment of impact, a wave of energy causes the crust and mantle to rise, leaving behind a dome and a bull’s-eye in the center. The rocky ridges peak further from the center. The heat melts rocks and changes minerals.
Scientists study melted rocks, altered minerals and other products to learn more about our Solar System and the origins of certain life forms. Sometimes, Huber said, the heat after an impact can create an environment where life can grow. Or the crater’s rocks can provide clues to the amount of energy released during the impact, which is sometimes enough to cause the extinction of, for example, the dinosaurs.
But over the past two billion years, erosion has worn away about six miles of craters from its surface. Huber wanted to see whether rocks at that depth still showed geophysical signs of the impact event, such as differences in density and porosity.
The team took rock core samples along a 14-mile stretch, comparing the physical properties of the crater rock with unimpacted rock. They also modeled the impact event and compared their samples with what the model showed in terms of the physical properties of the rocks.
The results were surprising, but not in a good way. They found that these rocks were indistinguishable from rocks that had not experienced an asteroid shock. The porosity, density, and speed of movement of sound waves through rock, for example, are identical to rock that has not experienced shaking.
“If we bury those rocks and we only find them in drill core, for example, then there’s a good chance that no one will realize that it was an impact,” Huber said. “At some point, we lost all the features that made the crater a crater.”
Marine geologist Ted Moore, who was not involved in the research, said the study’s explanation of the absence of mysterious old craters was ‘spot on.’ He added that the most effective mechanism of erosion is the crushing action of flowing ice sheets on land, and ice covered most of the continents during past ice ages.
Additionally, Moore, who is a professor at the University of Michigan, points out that impact asteroid it could also be hidden in our oceans, which cover more than 70% of our planet. As the size of the oceans and continents changed due to Earth’s evolution, some of these changes may have obscured some of the craters that could be identified.
“This study suggests that a large part of our planet’s geological history may be lost forever because it was recycled by our very active planet,” said Ania Losiak, a planetary scientist at the Polish Academy of Sciences’s Institute of Geological Sciences, Poland, who was not involved in the research.
But learning about Earth’s early history has not been completely lost. Losiak emphasized that scientists can study other planetary bodies, such as the Moon which has similar giant impact craters that are less affected by erosion.
Even though it’s difficult to find, scientists hope there’s a chance someone will get lucky and find this incredibly well-preserved crater on Earth. “We’re constantly looking for new structures because there’s always something odd and strange around,” Huber said.
Watch the video “Scientists in England Start Examining Samples of the Asteroid Bennu”
(rns/agt)
2024-01-20 15:30:30
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