The impact of a sufficiently large asteroid or comet is one of the theories that have been put forward to explain why dinosaurs, as well as many other plant and animal species, became extinct 65 million years ago. why would this extinction-level event have had such a major impact on life on earth? o the toxic fumes produced meant that the dinosaurs could no longer breathe. it increased the temperature of the planet. it created enormous tidal waves and huge forest fires. it produced dust and other particulates that would block out the sun.