Question

During the Paleozoic Era there was explosion of life in the oceans. Most of the continents were covered in warm, shallow seas. What is true about life on Earth at this time?

Answer 1

This event may have caused the climate changes that led to mass extinction event
The Appalachian Mtns were formed during this time
Invertebrates were dominate
Fish emerged
Fish led to the arrival of amphibians 
At the end if the Paleozoic, the largest mass extinction in history wiped out approximately 90% all marine animal species and 70% of land animals.