THE’asteroid which caused theextinction of the dinosaurs non-avian 66 million years agoas well as over 70% of living species at the time, probably came from the Solar System externalbeyond the orbit of Jupiter, according to a new study presented in the journal Science. The hypothesis that an asteroid caused the Cretaceous mass extinction gained ground in 1990 thanks to the discovery of iridium in Umbria. The result is due to theisotopic analysis of samples from the Earth’s subsurface at the depths of the impact deposits that occurred 66 million years ago in the region of present-day Chicxulub, Mexico, where a huge crater was formed. These samples show a content of isotopes of ruthenium which is compatible with those of the carbonaceous asteroidswhich reside beyond the orbit of Jupiter. The results of the study seem to definitively exclude the hypothesis that the extinction of the dinosaurs was caused by a comet, or by an object of the asteroid belt between Mars and Jupiter.
How the mass extinction of dinosaurs happened
In the last 500 million years Several mass extinction events have occurred on Earth, but the most famous of all was when an asteroid the size of about 10-15 km (larger than Mount Everest) hit the Earth at a speed of about 50,000 km/h in the region of today Chicxulubin Mexico. The impact with the shallow waters of the Gulf of Mexico created a crater with 145 kilometers in diametercausing destruction on a planetary scale, hurling millions of tons of debris into the atmosphere, blocking the Sun, and plunging the Earth into a nuclear winter. This apocalyptic event caused the extinction more than 70% of living speciesincluding the non-avian dinosaurscreating the conditions for the evolution of mammals and, therefore, of humans.
How we found out about the origin of the asteroid
Most scientists agree that the Chicxulub crater was created by a object coming from our Solar System that impacted the Earth 66 million years ago. However, until now there was no unequivocal consent on the region of origin of the object within the Solar System itself, nor was there any consensus on the nature of the objectwhich could equally have been an asteroid or a comet.
The study presented in the journal Science from the team of Mario Fischer-Gödde of the University of Cologne (Germany) seems to finally shed light on these aspects. The Chicxulub impact of 66 million years ago created in the Earth’s crust a global layer of deposits of material that marks the geological boundary between the Cretaceous and Paleogene. By studying the chemical composition of these deposits in various areas of the Earth, it is possible to try to trace the chemical composition of the object that created these deposits.
The team of scientists then measured the chemical composition of the deposits both in the Chicxulub regionboth in others five impact sites happened between 36 and 470 million years agotogether with even older impact layers, dating back to 3.5-3.2 billion years ago. In particular, scientists focused on one specific element, the rutheniumand on his isotopes (atoms with the same number of protons, but different numbers of neutrons). The isotopic composition of ruthenium is like a characteristic signature comparable to that of different types of asteroids or comets.
Where Did the Asteroid That Killed the Dinosaurs Come From?
The results of the comparison of the isotopic composition of ruthenium show that the object that created the crater Chicxulub is compatible with a carbonaceous asteroid (rich in carbon-based molecules), originated in Outer Solar Systembeyond the orbit of Jupiter. This asteroid was probably pushed toward Earth by collisions with other space rocks or by gravitational influences in the outer Solar System, where gas giants like Jupiter generate immense tidal forces capable of disturbing otherwise stable asteroid orbits.
The other impact sites analyzed instead have isotopic signatures more consistent with the siliceous asteroidswhich formed closer to the Sun. The ancient samples of the layer dating back to 3.5-3.2 billion years are instead consistent with the impacts of carbonaceous asteroids that affected the Earth during the final stages of its formation. The results of the study therefore seem to make to set definitively thehypothesis that the dinosaurs became extinct due to the impact with a comet.
