7. the k-t extinction event

The K-T extinction event occurred 65.5 million years ago. It was a sudden event that saw the extinction off three quarters of all life on earth (plants and animals). With the exception of some turtles and crocodiles, no four limbed animals over the weight of 55 pounds survived this event and it saw the extinction of all non-avian dinosaurs.

The K-T event is marked in many places around the world in both terrestrial and marine rocks as a thin iridium-rich layer.This layer was deposited by a massive comet or asteroid, roughly 6 to 9 miles wide. The impact would have had a devastating effect on the global climate, likely resulting in an impact winter (a prolonged period of cold weather resulting from an enormous amount of dust, ash and other material being thrown into the atmosphere and blocking out the sun).This prolonged winter would have halted photosynthesis in plants on the land and plankton in the sea. Entire food chains were destroyed; once herbivores struggled to find food and died of starvation, so the carnivores soon followed.

In geological terms, the dinosaurs were wiped out in the blink of an eye and their 180 million year reign was brought to an abrupt end. However their extinction led to an explosion in the diversity of mammals who soon went on to become the dominant land vertebrates.