Earth's Oldest Crater May Have Jumpstarted All Life
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Geologists have now unearthed evidence of a 3.5 billion-year-old crater found in a layer of Australian rock.
Shatter cones, which are features caused by the shockwave of a hypervelocity meteorite impact, are evidence that something hit this region when Earth was young.
Impact craters this old have the potential to tell us not only how Earth evolved but how the earliest impacts created the conditions for life to emerge.
Long before the asteroid that ended the dinosaurs crashed to Earth, our planet was being bombarded by space rocks that left behind enormous craters. The reign of T. rex and Co. ended around a measly 66 million years ago, but geologists just discovered that what is now considered the oldest impact crater on Earth is nearly 3.5 billion years old.
Earth itself formed only a billion years prior to an ancient collision that slammed what is now Australia. The earliest known fossils of single-celled organisms date from around the time the crater was formed, the Archaean era, which overlapped with the end of the Late Heavy Bombardment. It is thought, that during this epoch, a disruption in planetary orbits threw asteroids from the asteroid belt towards the planets of the inner Solar System.
Lunar craters that are relics of the Late Heavy Bombardment are mostly obvious, since the Moon has hardly any weather phenomena (because of the lack of atmosphere), no plate tectonics, no liquid water, and no life. These craters are much more difficult to find on Earth. Eons of erosion and shifting of continents may have buried them and possibly erased them, which is why they are so rare, but not only can we add this new one to our list, but it's the oldest one we've ever found.
Led by Curtin University geologists Chris Kirkland and Tim Johnson, a research team unearthed this primeval crater beneath rock layers in the East Pilbara Terrane of Western Australia. The oldest Archaean crater before this discovery went back only 2.2 billion years.
'On Earth, this early impact record has seemingly been lost, reflecting the destructive efficiency of erosion and subduction in recycling primary (basaltic, oceanic) crust back into the convecting mantle,' Kirkland and Johnson said in a study recently published in Nature Communications.
Meteorite impacts are said to have triggered plate tectonics and volcanic activity on a young Earth, forming cratons, or huge chunks of crust that were the beginnings of the continents. Part of the Pilbara Craton, the East Pilbara Terrane is a nearly pristine fragment of crust around 200 km (124 miles) in diameter. The crater was unearthed near the center of this region and identified by shatter cones and spherules. These features, found in a 3.5 billion-year-old layer of silicate rocks mashed up with older rocks, suggest at least two Archaean impacts.
When a meteorite hits the surface, shock waves from the impact propagate through layers of rock, cracking the rock in such a way that creates cone formations. The ridges left in these shatter cones capture a permanent reminder of the shockwave. Particles of melted and re-solidified rock (spherules) were kicked up by the impact and fell onto the surrounding area. Whether the spherules found at East Pilbara Terrane have a cosmic or terrestrial origin is debatable, but they are still evidence that something plummeted through the atmosphere and crashed to Earth.
Whatever hit Australia billions of years ago possibly did more than just leave an enormous scar. Meteorite impacts might have made it possible for life to survive. Some of the oldest fossils of microbial life are close in age or just slightly older than the Pilbara crater.
'Impact craters may have provided the physical and chemical environments required for life to emerge on Earth and elsewhere,' the researchers said in the same study.
Could that 'elsewhere' have been Mars? There is no evidence yet, but NASA's Perseverance rover keeps searching as it crawls across the barren expanse of Jezero Crater, which used to be an ancient crater lake that has long since dried up. Finding more of the most ancient craters on Earth might tell us something about Archaean remnants beyond our planet.
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