As any child can tell you, the Mesozoic Era ends with the extinction of the dinosaurs. Most geologists think the cause of that extinction was the impact of an enormous meteorite that hit the Yucatan Peninsula in Mexico. As the theory goes, the impact was so large it led to global changes in the composition of the atmosphere. Smoke and dust raised by the collision blocked the sun’s light for a time, making temperatures drop and plants die off. Many species of both plants and animals didn’t live through the crisis, as parts of the food web simply fell apart.
The extinction that carried off the dinosaurs is one of five mass extinctions in the geologic record during the last three eras of geologic time – the time marked by animals of sharply increasing complexity first in the seas and then on land. Because the dinosaurs are famous the world around, the extinction that killed them is often discussed in public circles. But the causes of the other four mass extinctions are just as interesting to scientists.
Recently new evidence has been brought to light about the mass extinction that occurred during, rather than at the end, of the Mesozoic Era. The time in question stands at the boundary between the Triassic Period and the Jurassic Period (think of the movie Jurassic Park if you want a little help with these names).
The extinction at issue saw the end of three quarters of the species then living in the seas and on land. The massive die off helped clear the ground for the dominance of the dinosaurs for more than 100 million years.
In the early Mesozoic what is now North America was united with Europe as part of a supercontinent called Pangaea. Pangaea broke up into separate continents as geologic time unfolded. Volcanic rocks of the same type and age are found along the East Coast and in Morocco, areas that were next to each other in the Triassic. The rocks resulted from a giant rift in the crust of the Earth, one that ultimately grew to become the Atlantic Ocean.
The more we learn about major extinctions, the more respect we must have for the ferocity of Mother Nature. Let’s hope we don’t live long enough to see her bare her volcanic claws once more.
Dr. E. Kirsten Peters was trained as a geologist at Princeton and Harvard. This column is a service of the College of Agricultural, Human and Natural Resource Sciences at Washington State University.