The Earth is frequently hit by rocks from our solar system, most of them coming from the asteroid belt, between Mars and Jupiter; These rocks tend to disintegrate as they enter the atmosphere and do not bring major consequences for the inhabitants of our planet. But sometimes these rocks are big enough to trigger a cataclysm capable of wiping out most species, as happened 66 million years ago. We know that this impact opened a crater 180 kilometers in diameter; but it is by no means the oldest character.
The discovery in January 2020 of one of the oldest surviving craters is also related to the end of the most intense and lasting glaciation the planet has ever experienced : the ‘Snowball Earth’ period.
The remains of the impact in question have been found in Western Australia, and correspond to a crater 70 kilometers in diameter with an age of more than 2.229 million years: the Yarrabubba crater , as it has been baptized.
But there is more.
Not only has this unprecedented crater been identified; Rather, it has been linked to one of the most interesting events in Earth’s history.
The ‘Snowball Earth’ hypothesis is still controversial . There is no evidence yet that the Earth was ever entirely covered in ice, but what scientists are sure of is that there were severe ice ages in that period, if not all, over most of the planet. The thaw brought with it a great explosion of marine life: the Cambrian period, in which organisms such as trilobites, anomalocaris (ancestors of insects) and picaias emerged, the first organisms with something similar to a spine.
Researchers believe that the Yarrabubba crater is the remnant of an ancient impact that vaporized billions of liters of water , freeing Earth from its icy prison, and ushering in an unprecedented explosion of life. Until now, the hypothesis that scientists used to explain the end of this glacial period was intense volcanic activity. But, with this finding, we may have to rewrite the history of our planet and, incidentally, ours as well.
How do scientists know the age of Yarrabubba crater?
Dating ancient craters is not easy : these places tend to be poorly preserved because erosion and tectonic events such as earthquakes progressively obliterate the geological past, as the researchers detail in their paper, published in the journal Nature Communications .
The team looked for evidence of “shock recrystallization” in minerals such as zircon and monazite within the crater. But finding that record in minerals involved looking for microscopic grains. The uranium in the grains helped scientists determine a precise date, which coincided with the Great Ice Age.
The researchers speculate on the idea that when the meteorite struck Yarrabubba, this place was covered in ice, like much of the rest of the Earth at the time: “The impact fits within the context of the Earth coming out of cold conditions.” they explain.
The massive attack could have sent billions of tons of vaporized ice into the atmosphere, according to models led by the team: “On an ice sheet, the impact would have released a lot of water vapor, which is still a greenhouse gas. more efficient than carbon dioxide, “in the words of lead author Timmons Erickson of NASA’s Johnson Space Center and the Curtin School of Earth and Planetary Sciences.” That, in turn, could lead to global warming “.
Attention : what is a fact is the dating of the crater, but that this crater triggered a massive thaw is just a hypothesis made by scientists.
Those skeptical of the findings of this study say that large meteorite impacts are more often associated with cooling events than with global warming. In addition, they question that an object that leaves a crater of ‘only’ 70 kilometers is capable of evaporating such a quantity of ice, and unleashing such a decisive climate change.
