Sometimes, too many organisms in one place will cause a poor living environment for others. There are different time scales for ecological crises ranging anywhere from a few months to millions of years. Extinction events can affect many species or just a few individual species. Human activities, like oil spills, can cause local crises as well as global crises like global warming. Even with a local crisis, the loss of a few species can have a disastrous effect on the survival of others in the food chain. A global crisis can result in a loss of nearly all species on Earth. The most common example of such a crisis is the extinction of the dinosaurs