The Ordovician Mass Extinction (450-435 MYA)

The Ordovician Mass Extinction occurred long before any animals had appeared on land.  It was the second most devastating mass extinction to ever affect the planet. As much as 50% of all species disappeared forever. The trilobites, many legged shelled creatures, were most affected. The cause of this extinction was due to a long ice age. The water began to freeze into great ice sheets at the South Pole, and the sea levels dropped dramatically. Another possibility is that a giant star, thousands of times bigger than our own sun, far out in space, started to collapse in on itself. Then it exploded, sending highly harmful gamma rays toward the Earth, poisoning the seas and atmosphere with high radioactivity.

The Ordovician sea before the mass extincion