The earliest impact scars from asteroids that bombarded Earth's surface may be lost forever to the ravages of time.
vertical erosion of
around 10 kilometers of material is sufficient to erase even the largest craters. Vredefort has experienced an estimated 7 to 10 kilometers of vertical erosion. All that's left is a semicircular ring of hills, and some smaller features, as well as invisible alterations underground found in gravity mapping surveys.Huber and his team wanted to know what was happening, not above ground, but below it, so they took rock core samples from different points in the crater.
The results showed that the odds are not good for finding older craters. Although some impact minerals and melt could be identified within the crater, the rocks in the outer regions were indistinguishable from non-impact rocks around them.."The difference, where there was any, was incredibly muted. It took us a while to really make sense of the data. Ten kilometers of erosion and all the geophysical evidence of the impact just disappears, even with the largest craters.
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