It has already been defined as the oldest meteoric impact crater ever identified on Earth, the one dated in Western Australia, which, according to geologists and researchers, was formed by an impact that occurred over 2.2 billion years ago. The study for the first time performs a precise dating of the Yarrabubba crater estimating the date in 2.229 billion years, 200 million years more than other old impact craters identified on our planet.
Dating with this precision impact craters so ancient is not at all easy: the Earth is a planet more than alive and, even just considering the tectonic events, including earthquakes themselves, one would expect that after 2.2 billion years a crater remains no longer perceptible as it is progressively erased by the geological action of the planet.
In this case, the researchers have made a noteworthy effort and, in their study published in Nature Communications, they explain how they managed to date such a crater.
First of all, they looked for special minerals present in the site, minerals that were the result of the alteration of the structure of various materials following the impact, including zircon and monazite.
Using special high-tech scanning processes, including ion microprobes, the researchers found and identified the uranium present in microscopic granules and were able to calculate a precise date. Among other things, at that time the Earth was in a deep freeze phase called “Snowball Earth.”
This means that at the moment of impact not only a crater was created (about 70 km wide) but several tons of ice vaporized into the atmosphere (up to half a trillion tons according to the researchers). Water vapor, in itself, is an excellent greenhouse gas. At this point the suspicion arises: did this impact event contribute to the melting of the ice that followed the snowball Earth?
At the moment there is no evidence to prove such a thing and it is only speculation. Further studies will be needed to determine whether such an impact can really cause far-reaching climate change in a completely frozen world like the Snowball Earth.
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