Stock Photo - 'Death of the dinosaurs.  Artwork of two  Tyrannos- aurus rex dinosaurs attacking a Triceratops (lower right), oblivious to the asteroids about to strike the  Earth  behind  them ... .   The  impact  of a huge asteroid or comet may have caused  the  extinction of  the dinosaurs and 70% of all species on Earth. The impact occurred about 65 million years ago  at the  end of the Cretaceous geological period.  The object,  thought to be  10-20  kilometres  across, struck  the  Earth  at  Chicxulub  on  the Yucatan peninsula, Mexico. It threw huge amounts of debris into  the upper atmosphere,  blocking out sunlight and causing global climate changes.