Researchers in the USA and Japan say they may have found the cause of the first mass extinction of life.

There have been five mass extinctions since the divergent evolution of early animals 600 -450 million years ago. The cause of the third and fourth was volcanic activity, while an asteroid impact led to the fifth. But triggers of the first and second mass extinctions had, until now, been unknown.  […]

Source:  https://www.geologyin.com/2017/05/large-volcanic-eruption-may-have-caused.html