- Human activities that threaten biodiversity
- Mutation as a source of variation
- Invasive species
- How did all dinosaurs except birds go extinct?
- Were dinosaurs undergoing long-term decline before mass extinction?
- Human impact on ecosystems review
- Introduced species and biodiversity
- How does climate change affect biodiversity?
- Demystifying ocean acidification and biodiversity impacts
- Biodiversity and extinction, then and now
- Threats to biodiversity
The extinction of non-avian dinosaurs except birds at the end of the Cretaceous has intrigued paleontologists for more than a century. One theory is that an asteroid impact 65 million years ago off the coast of Mexico generated massive tsunamis, with impact debris cutting off sunlight for months, stopping photosynthesis and causing freezing temperatures. Chemical reactions in the atmosphere caused acid rain and long-term global warming, all of which extinguished non-avian dinosaurs. However, at the same time, massive lava flows erupted across what is now southwest India. The eruptions probably caused many of the same effects as the asteroid impact. Although most scientists believe that the impact was the final blow for non-avian dinosaurs, both events could well have played a role. Created by American Museum of Natural History.
The question of non-bird dinosaur extinction is really an open one, I mean certainly that there's a tremendous amount of evidence, in fact that there's no doubt that at the time the dinosaurs went extinct a large meteorite or asteroid hit the planet somewhere off the Yucatan Peninsula in Mexico. However, directly tying this event to the disappearance of the terestrial fauna is very difficult and that's just because our sample is so small there's only a couple places in the world where both dinosaur fossils as well as evidence of the impact are preserved both of those are in western North America, so we don't know whether it was an instantaneous event we don't know whether the dinosaurs in the southern hemisphere, like held on for millions of years afterwards, we just don't have the record to be able to determine that. One thing we do know though, is that certainly that the dinosaurs, non-bird dinosaurs appear to be coming more and more rare, less common as you approach the time when the meteroite hit about sixty five point four million years ago so that it's not like everything was going great, and then you just had this massive cataclysmic event and everything disappeared, we know that stuff was changing, stuff was changing quickly. At the same time there was a huge amount of volcanic activity especially from places in western India, and interestingly enough this coincides with around the time of the asteroid impact so many paleontologists feel that it was a combination of factors, maybe both asteroids and volcanos that did the non-bird dinosaurs in, and I should emphasize not just that non-avian or non-bird dinosaurs but many many other animals and plants, in fact we estimate that maybe as much as seventy-five percent of all the species that lived on the earth at that time went extinct during this very dramatic event.