1. Encyclopędia Britannica - The Asteroid Theory
   An Encyclopedia Britannica article on the extinction of dinosaurs, asteroid theory
   http: //britannica.com/bcom/eb/article/8/0,5716...
   
   
2. Encyclopędia Britannica : Extinction of Dinosaurs
   An Encyclopedia Britannica article on the Extinction of Dinosaurs.
   http: //britannica.com/bcom/eb/article/0/0,5716...