A giant meteorite impact to put an end to the dinosaurs, another to diversify life!
Illustration of two giant meteorite falls during the Cretaceous. © Generated on Bing Creator by Brice Haziza
A law of series? However, we learn that this concept is just a cognitive bias. But tell that to the dinosaurs who would have seen two meteorites fall on Earth in a very short time: one well-known, about 10 km, in Mexico; the other, more modest, perhaps 400 m, in Africa, near the Guinea Sea. The discovery was published on October 3, 2024 on Nature Communications Earth & Environment.
Other teams of geologists have shown that there is a crater of around 600 km in Australia, which is linked to an impact around 550 million years ago. It could therefore coincide with the Ediacaran mass extinction, which shortly preceded the Cambrian explosion of lifeoften considered to be the beginnings of animal life as we know it.
In Australia, a 600 km crater probably identified
Geological map of the non-concentric impact structure dated to approximately 550 million years ago. © Daniel Connelly
Collaborative work has revealed the existence of this colossal 600 km crater in Australia. These are molten rocks near the center of the crater, shocked minerals – including diamonds – and quantities of iridium which, placed end to end, led to the trail of this astonishing structure, because it is not concentric (but which can very explained well according to the angle of impact of the meteorite).
Where this discovery is of great importance is that it provides information on the estimated size of the impactor. For a 600 km crater, we can infer a meteorite of around 20 km in diameter, which is even larger than the one responsible for the Cretaceous extinction and the majority of dinosaurs!
The other important point is the concordance of the periods. 550 million years ago, the Earth underwent a massive extinction, that of the Ediacaran which shortly preceded the great Cambrian diversification of animal life. The latter is perhaps the result of a longer process than usually presentedthe subject being debated. In any case, a major impact event concomitant with this period is remarkable to say the least.
66 million years ago, Earth without planetary defense
Location of the crater dated 66 million years ago and located in the central Atlantic, near the Guinea Sea (reconstructed by Gplates). © Uisdean Nicholson et al (Nature Communications Earth and Environment)
Another equally remarkable discovery: near the Guinea Sea, an 8.5 km crater exists under 300 m of sediment. It was in 2022 that the seismic imaging technique revealed this very circular crater, named Nadir. It would therefore be of a much less impressive size than that of Chixculub, around 200 km, but its dating is puzzling, because it would be 66 million years old! It could be a fragment of the famous Mexican meteorite or another impact only correlated in time.
8.5 km crater near the Guinea Sea. © Uisdean Nicholson et al (Nature Communications Earth and Environment)
Researchers also believe that the impact would have triggered an 800 m high tsunami that crossed the Atlantic Ocean.
Diagram of the different stages of the impact leading to the 800 m tsunami. © Uisdean Nicholson et al (Nature Communications Earth and Environment)
