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 a crack in the Earth’s surface 60 miles wide, but the crater became three times wider as its walls collapsed and the rocks beneath began bouncing. Scientists say the impact was larger and more energetic than the impact of the asteroid that killed the dinosaurs.
At the moment, Vredefort Crater, this is the name of the crater, did not have the appearance of a basin at the time of its formation and was certainly not the scene of a global disaster. Severe erosion leaves only part of the ring still visible. Some parts of the crater also include agricultural land. Finding so much evidence from this crater is a stroke of luck, scientists say.
A new study finds that Earth’s oldest craters, which may 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. According to new research, if the impact event had occurred 200 million years earlier, erosion processes would have obliterated the crater by now. To today’s scientists it appears that the asteroid never hit.
“It’s not that Vredefort disappeared. All his ‘cousins’ disappeared,” said Matthew S. Huber, the study’s lead author. “It’s a coincidence that we have so much evidence in our possession about Vredefort,” he was quoted as saying by the Washington Post.
A 2 billion-year-old crater may seem ancient, but it represents only half of Earth’s history. Craters have occurred since the beginning of the Solar System, appearing on the surface of many rocky bodies. Geologists have counted around 200 impact craters on the Earth’s surface, the oldest of which date back around 2 billion years. But Huber says there should be more.
“We recognize that hugely impactful events 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 actually doesn’t exist,” she 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, researchers did some digging Vredefort Crater 190 miles wide. Upon impact, a wave of energy causes the crust and mantle to rise up, leaving behind a dome and a target in the center. The rocky ridges peak farthest from the center. Heat melts rocks and changes minerals.
Scientists study molten rocks, weathered minerals, and other products to learn more about our Solar System and the origins of some life forms. Sometimes, Huber said, the heat after an impact can create an environment in which life can grow. Or the rocks in the crater may provide clues to the amount of energy released during the impact, which is sometimes enough to cause the extinction of, for example, dinosaurs.
But over the past two billion years, erosion has stripped about six miles of craters from its surface. Huber wanted to see if the rocks at that depth still showed geophysical signs of the impact event, such as differences in density and porosity.
The team took rock samples along a 14-mile stretch, comparing the physical properties of the crater rock to those of unaffected rock. They also modeled the impact event and compared their samples to 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 suffered an asteroid shock. The porosity, density and speed of movement of sound waves through rock, for example, are identical to those of rock that has not been shaken.
“If we bury those rocks and only find them in the 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 for the absence of mysterious old craters was “spot on.” He added that the most effective erosion mechanism is the crushing action of ice sheets flowing over the land, and ice covered most continents during past ice ages.
Furthermore, Moore, a professor at the University of Michigan, highlights this impact asteroid it may also be hidden in our oceans, which cover more than 70% of our planet. As the size of the oceans and continents has changed due to the Earth’s evolution, some of these changes may have obscured some of the craters that could be identified.
“This study suggests that much of our planet’s geological history may be lost forever because it has been recycled by our very active planet,” said Ania Losiak, a planetary scientist at the Institute of Geological Sciences of the Polish Academy of Sciences , in Poland, who was not involved in the research.
But knowledge of Earth’s early history has not been completely lost. Losiak pointed out that scientists can study other planetary bodies, such as the Moon which has similar giant impact craters that are less affected by erosion.
Although it is difficult to find, scientists hope that there is a chance that someone will get lucky and find this incredibly well-preserved crater on Earth. “We’re constantly looking for new facilities because there’s always something strange and weird going on,” Huber said.
Watch video “Scientists in England begin examining samples from asteroid Bennu”
(rns/agt)
2024-01-20 15:30:30
#Ancient #crater #full #mysteries #history #Earth #scientists