Overberg Geoscientists Group
66 Mya
Death of Dinosaurs
In 1980 Luis & Walter Alvarez, launched the idea that the event that caused the mass extinction of 75% of all plant and animal species on Earth including all non-avian tetrapods larger than 25kg, as well as the dinosaurs, was the impact of a huge meteorite.
They came to this conclusion by studying the rocks on either side of a thin clay band which marked the boundary of the preceding Cretaceous era and the subsequent Paleogene. The layer was dated at 66 million years ago. It was found to be very rich in Iridium, a very rare element on Earth, but much more common in asteroids and meteors. The initial discovery was in Italy, but the layer has since been found worldwide
The next task was to determine where the huge impact occurred. There was evidence of ‘mega tsunamis’ in a number of sites including Brazil, Mexico and the USA. So that area was investigated, and an enormous crater was found just off the Yucatan Peninsula in Mexico. The crater was dated and found to be at the exact time of the mass extinction some 66 million years ago.
The impact had worldwide ramifications, and its effects have been found on all continents.
The crater it produced was around 180 km in diameter and massive amounts of dust and debris were sent up into the atmosphere. This then created a decrease in sunlight and temperature around the globe. Leading to an impact on the vegetation that used photosynthesis (fungi were not really impacted).
The major effects were also on the largest animals around at the time, these were the reptiles and, in particular, the dinosaurs. All non-avian dinosaurs did not survive. The only reptiles that did survive were crocodiles, some sea turtles, and the snake/lizard families. These were all cold blooded and could stay alive without eating for longer periods.
Creatures that lived in the open seas were better off than those living on the bottom of the seas and in shallow water. It is thought that this was due to an increase in acidity caused by dust from the impact and the decrease in temperature of the warm oceans.
More than 75% of all life died.
This, of course, led to an opening up of many habitats to those life forms that did survive. Mammals and birds being the principal beneficiaries. Mammals expanded rapidly into many of the now available environments, including air and water.
It would be a very different world now if the Asteroid had not impacted and affected the planet Earth 66 million years ago.
Further Reading:
​
Schulte, Peter; et al. (5 March 2010). "The Chicxulub Asteroid Impact and Mass Extinction at the Cretaceous-Paleogene Boundary" (PDF). Science. 327
Alvarez, Luis (10 March 1981). "The Asteroid and the Dinosaur (Nova S08E08, 1981)"
"Extraterrestrial cause for the Cretaceous–Tertiary extinction" (PDF). Science. 208
Henehan, Michael J. (21 October 2019). "Rapid ocean acidification and protracted Earth system recovery followed the end-Cretaceous Chicxulub impact". Proceedings of the National Academy of Sciences of the United States of America. 116
Pope, K. O.; d'Hondt, S. L.; Marshall. C. R. (1998). "Meteorite impact and the mass extinction of species at the Cretaceous/Tertiary boundary". Proceedings of the National Academy of Sciences of the United States of America. 95 (19): 11028–11029.
D J Mourant Aug 2023