66 million years ago a meteorite crashed into Earth at more than 70 thousand kilometers per hourcausing the raising of an enormous amount of dust into the atmosphere, a mega-tsunami with waves hundreds of meters high and the extinction of the dinosaurs. But how can we say that it was a meteorite that made the dinosaurs extinct? You won’t believe it, but the currently most accepted answer has to do with a small town near Gubbio, in Umbria.
The characteristics of the meteorite
They have happened throughout Earth’s history 5 great mass extinctionsthe last of which – precisely – is that of Cretaceous (what is commonly called the “dinosaur extinction”) which dates back to 66 million years ago. Incidentally, it would be more correct to talk about dinosaurs not aviansthat is, those that do not fly, because the avian dinosaurs partly survived and then evolved into today’s birds. Do you think that this event had such an impact on the planet that it was chosen as the border line between two geological eras, that is, between Mesozoic and the Cenozoic (or Tertiary).
As we anticipated, this extinction was most likely caused by a asteroid coming from beyondorbit of Jupiter which had a diameter between 10 and 15 km – therefore larger than Mount Everest – and which would have crashed into the earth at approximately 20 km/second. The impact created the Chicxulub crater with 180 km in diameterone of the largest ever observed on our planet and which is located in Gulf of Mexico (half at sea and half on land near the Yucatan Peninsula).
Why did dinosaurs become extinct?
The impact of the meteorite with the ground it was so violent which the rocky body disintegrated, projecting into the atmosphere fragments set on fire and debris that entered the atmosphere and then reached various areas of the world and caused forest fires worldwide. According to what NASA reported, it is estimated that hundreds of them were released into the atmosphere billion tons of CO2sulfur dioxide and water vapour.

All this ash and dust in the atmosphere they blocked out much of the sunlightmaking the growth of plants difficult and therefore also creating problems for herbivores and, consequently, for carnivores. But not only that! The meteorite impact caused such violent earthquakes to shake the planet for several weeks, with an amount of energy released that is estimated to be 50 thousand times greater compared to that of the 2004 Sumatra earthquake, which it measured 9.1 magnitude. Finally – the icing on the cake – the meteorite also caused one global tsunamiwith waves hundreds of meters high.
In short, it was an unimaginable catastrophe. We obviously don’t know all the details of this extinction, for example we don’t know exactly how long it took the dinosaurs to become extinct. However, we know for sure that, in a relatively short period of time, the 75% of all species were wiped out from the planet.
Who went extinct 66 million years ago?
This is usually known as the extinction of dinosaurs, but it’s not that all dinosaur species became extinct at that exact moment, some had already been extinct for some time. Among the dinosaurs that actually became extinct due to the meteorite we find some names that we all know, such as the T-Rexi Sauropods, the Triceratops or him Pterosaurs (which however – be careful – are not dinosaurs but reptiles, even if they are usually considered by most to be dinosaurs).

Interestingly, although dinosaurs have been hit hard, the same cannot be said for other classes, such as plant, the gastropods, the molluscs, The amphibians, the mammals and some reptiles, such as lizards, snakes and crocodiles. Of course, they didn’t fare very well, and many species went extinct anyway. But there is a difference between having some extinct species and being completely extinct.
This is probably linked to several factors: first of all, non-avian dinosaurs had larger on averageand therefore it was more difficult for them to take shelter during falling fragments or during fires. Furthermore, small mammals could still rely on seeds and insects to survive, whereas large reptiles needed large quantities of plants which in fact no longer existed.
How do we know that dinosaurs became extinct due to a meteorite?
The answer, strange as it may seem, has to do with a small town in Umbria, near Gubbio. We are talking about the Bottaccione Gorge and in the early 1960s the micropaleontologist Isabella Premoli Silvatogether with a Swiss colleague, dated the outcropping rocks using planktonic foraminifera and identified a very clear limit between the Cretaceous and the Paleocene. This limit is represented by a dark red clay layer And free of foraminifera, which is found among pink limestones. In these limestones, however, the foraminifera in the last layer of the Cretaceous are completely different from those in the first layer of the Paleogene. The level of dark red clay therefore documents the almost total death of the calcareous plankton of the oceans.
In the 1970s, a group of American geologists took advantage of these studies and began to analyze in detail the succession of rocks in the Bottaccione Gorge. So this place is also visited by the geologist Walter Álvarez and from his father Luis Álvarez – famous for receiving a Nobel Prize for Physics in the same year.

They focused their attention on the clay level and decided to carry out in-depth analyzes to characterize its composition. They quickly realized that this level was full of iridium, a very rare transition metal in terrestrial rocks and abundant, however, in bodies of extraterrestrial origin such as asteroids and cosmic dust. So since the 1980s the idea that the extinction was due to the impact with a body in the solar system has become increasingly stronger.
At this point only one last piece was missing, that is, understanding which body could have caused such a violent and sudden extinction.
The Chicxulub crater
It was soon realized that the main suspect was in Mexico: in fact there in the 60s an oil company during its explorations had observed ahuge circular structure partly on the mainland and partly offshore which is not particularly evident to the naked eye, because it is covered with sediments, but which from gravimetric analyzes – i.e. analyzes based on the measurement of the force of gravity – is extremely visible and formed by several concentric circles. This is precisely the Chicxulub crater we were talking about before.

Consider that initially it was believed that those signs were the remains of an ancient volcanic structure… even though there was various evidence that didn’t add up. Like there was a lot iridium, compatible with the values found in the Bottaccione clay level. Then the ad structure concentric rings it is typical of impact craters, in fact following the impact the crater becomes liquid due to the high temperatures, the center rises, forming a sort of plateau which then collapses, giving rise to several rings inside the crater itself.
Then, again, fragments with a composition similar to those found in the Chicxulub crater were observed but a 3-4000 km away from the crater. In short, these are just some of the pieces of evidence which, to date, allow us to say with a good degree of certainty that the extinction of the dinosaurs is linked to the impact of a huge meteorite.