Imagine that it is about 450 million years ago and you are some ancient form of marine life just floating along and minding your own business when all of a sudden there is a flash and everything, including you, is dead. 

The event you are imagining is known as the Ordovician extinction and one hypothesis is that a gamma ray burst, or series of bursts, could have been responsible for the mass extinction of almost 85% of all marine species on Earth. 

What are gamma rays? Where do they come from? Are they really that dangerous and if so, what makes them so deadly? Should we be worried? 

Find the answers to these questions in the following fascinating video by the Kurzgesagt YouTube channel. 

Watch the video and let us know what you think in the comments, but don't wait because the next extinction could be right around the corner!