What was the biggest catastrophe ever?

Answer 1

There have been several catastrophes throughout the life of the Earth that caused huge extinctions of life. The most recent was the arrival of an asteroid that struck the area that is now Yucatan about 65 million years ago. That asteroid disturbed the climate (mostly by blasting huge quantities of dust into the atmosphere) and the end of most of the dinosaurs. That, led to the ascension of mammals as the dominant land life form. That, in turn, led to humans who are busily manufacturing the next catastrophe themselves. So we could say that, in a sense, the Yucatan meteorite was a double whammy, catastrophe-wise.

Answer 2

The biggest catastrophe in terms of loss of life was the Black Death in the 14th century, estimated to have killed 75-200 million people. In terms of environmental impact, events like the Toba supervolcanic eruption around 75,000 years ago had a significant global impact.