The era that is defined by both a huge explosion in the diversity of life as well as the largest mass extinction is
proterozoic
paleozoic
mesozoic
cenozoic

The correct answer is The Paleozoic era. This was the time of the greatest mass extincition ever which was so sever that it took 30 million years for the biosphere to become normal again. It was so sever that the name for it is "The Great Dying". Not only were the normal animals affected, but it was the only recorded mass extinction of insects as well.