Montshire Minute: Dinosaur Extinction

Originally aired during the week of September 15, 2003

Monday

There have been several episodes of mass extinction in the earth's history. One of the most dramatic came about 65 million years ago, when the dinosaurs and many other plants and animals disappeared, along with about 75% of all marine creatures. Why did the dinosaurs, which survived and thrived for so long, die off so suddenly? Well, there are a lot of theories, including one by cartoonist Gary Larson. One of his Far Side drawings depicts dinosaurs smoking cigarettes, with the caption reading: "the real reason dinosaurs became extinct." That's silly of course. Cigarette packs didn't have warning labels when dinosaurs were alive! Seriously, there are many other theories that explain what "did in the dinosaurs." This week on Montshire minute we'll be exploring the possible reasons for the mass extinction that took place 65 million years ago.

Tuesday

About 65 million years ago a great mass extinction wiped out the dinosaurs, along with many other creatures on earth. One theory explaining this catastrophe is that dinosaur eggs could have been eaten by the growing number of mammals populating the planet. These mammals may have decided that dinosaur eggs, which are rich in protein, made a gourmet dinner. Hey, omelets all around! So, the theory goes, the survival rate dropped and dinosaurs gradually became extinct. However, we know that dinosaurs and mammals evolved together for most of the Mesozoic era. Why, all of a sudden, would predation of eggs have such a dramatic impact on the dinosaur population? So far, paleontologists haven't come up with evidence that supports the "mammal as predator" theory.

Wednesday

There is a thin layer of clay formed about 65 million years ago that may hold clues to the mystery of the sudden extinction of dinosaurs. This clay layer contains an unusual amount of the rare element iridium. We know that iridium mostly comes from dust drifting in outer space. A large meteorite would contain a lot of iridium. Iridium also can be found deep in the earth's crust. We also know there was a lot of volcanic activity near the end of the Cretaceous period, which may have released iridium. When a volcano erupts, it also sends ash, containing sulfuric acid and poisonous gases, into the air. Over several million years, a large number of active volcanoes could have created enough dust and soot to block out sunlight, producing climatic change. And the telltale iridium layer suggests that perhaps volcanic activity was one of the things that did in the dinos.

Thursday

One dinosaur extinction theory taken seriously by scientists is that a huge asteroid hit the earth about 65 million years ago. Large amounts of iridium - an element found in high concentrations in asteroids - have been found in rock formed 65 million years ago. In 1990, scientists dated a huge crater off the Yucatan peninsula to about the same time period. The crater, 180 kilometers in diameter, is the largest on earth. The asteroid would not have killed the dinosaurs all by itself, but resulting ash and dust released into the atmosphere could have blocked out sunlight, causing global cooling. Smaller animals might have been able to escape such a catastrophe by burrowing. But the dinosaurs would have been exposed to effects of climate change, not to mention hurricanes and firestorms that might have been caused by the impact.

Friday

This week on Montshire Minute we've been looking at some theories proposed to explain the sudden disappearance of the dinosaurs about 65 million years ago. There now seems to be little doubt that an asteroid hit the Earth at the end of the Cretaceous period, which contributed to the demise of the dinos. But many experts don't accept the asteroid theory as the only cause for the mass extinction. The fossil record shows that dinosaur diversity was already in decline. Volcanic activity and competition from other animals may also have been contributing causes. In this scenario, the asteroid impact may have been "the straw that broke the dinosaur's back." To learn more about the origins of dinosaurs and how they lived, visit Montshire's visiting exhibit Hatching the Past, now on display at the Montshire Museum.