The meteorite or asteroid impact theory states that around the same time dinosaurs died off, 65 million years ago, an asteroid (4-9 miles across) hit earth creating a giant crater in the Yucatan Peninsula. The impact would have kicked up a lot of dust and debris which caused global cooling as the sun's rays would not be able to penetrate this dust in the atmosphere easily. Giant fires would be set off as well as volcanic activity. Ecosystems would be impacted because the amount of light would decrease, affecting autotrophs or producers. This in turn would affect the consumers throughout the food webs. Many organisms went extinct including all the dinosaurs, many plants and larger animals. As the temperature dropped, organisms in ecosystems that were previously warmer might not be able to adapt and might have become extinct. It is thought that because dinosaurs were most likely warm--blooded, they would be unable to generate enough heat to keep their large bodies warm and this might have caused their demise. When they died off, it opened up new opportunities for other organisms to exploit. They would have new habitats, less predators and this would allow for natural selection and evolution to occur. Mammals which were insignificant when the dinosaurs were alive, would now have new ecosystems to expand into and over time, they evolved into the millions of different mammal species we have today.