WHY IS IT THAT SOME OF THE ORGANISMS GET EXTINCT OVER SOME PERIOD OF TIME

Question: WHY IS IT THAT SOME OF THE ORGANISMS GET EXTINCT OVER SOME PERIOD OF TIME
- Keywords:
  extinction,
  organism,
  time
Asked by abbb266 to George on 16 Jan 2017.
- George Githinji answered on 16 Jan 2017:
  
  Because the environment necessary for the existence of the organism changes. For example if the food is inadequate or the weather patterns change over time or drastically. If the ice at the north pole melts, all the polar bears that survive only in the cold environment will die and go extinct. In the case of the dinosaurs, scientists believe that an astroid hit the earth and caused global changes on planet followed by extinction of millions of species, but also new ones arose!