– January 22, 2020 – Science
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- The oldest crater is a godsend for studying the Earth’s climatic past.
The age of the oldest land impact crater has been estimated. This is the Yarrabubba Crater, located in Australia. On January 21, 2019, NASA announced that it was 2.229 billion years old. A study published the same day in the journal Nature Communications explains why this structure could help to better understand our planet’s past.
Yarrabubba Crater is located between the towns of Sandstone and Meekatharra in Western Australia. It is no longer possible to observe the original crater today, but it is identifiable through geological data. Scientists’ analyses lead them to conclude that this crater is “the oldest impact structure on Earth,” they write. The study looks at the possible effects that this impact might have had on the Earth’s climate, on a regional or global scale.
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The location of the Yarrabubba Crater // Source: Google Maps screenshot, annotation Numerama
Extraterrestrial impacts have certainly had consequences on the evolution of the environment on the Earth’s surface, the authors explain. Nevertheless, traces of these events are rare, as they are erased over time due to phenomena such as erosion or plate tectonics. One consequence of the lack of evidence of these past land-based impacts is that it is difficult to establish “links between impact events and point changes in the atmosphere, oceans, lithosphere and life” – except for the impact that would have led to the Cretaceous-Paleogene extinction, with the extinction of non-avian (i.e., non-bird) dinosaurs.
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Estimating the age of the crater is interesting because its formation seems to have occurred when the first ice caps and glaciers appeared on Earth, just after the arrival of oxygen in the atmosphere of our planet. The authors explore the possibility that the impact that formed this crater caused changes in the Earth’s climate. It is possible that the water vapour produced by the impact in the lower atmosphere may have resulted in rain and snow, without disturbing the long-term climate. But the impact could also have favoured “widespread glacial conditions“, due to an albedo effect of the clouds (their reflectivity).
A grain of zircon. // Source: Nasa (cropped photo)
To determine the age of the impact crater, scientists collected rock samples, which contained two types of minerals: zircon and monazite. The age of the rocks could be estimated from the uranium and lead contained in the minerals, observed under the microscope.
The search shouldn’t stop there. “While the 2.229 billion-year-old Yarrabubba structure represents the oldest dated impact crater on Earth, its coincidence with the end of Palaeoprerozoic glacial conditions requires careful examination,” scientists cautiously conclude.