How did volcanic activity affect many life forms in the Precambrian and Mesozoic Eras? plz help asap

Question

How did volcanic activity affect many life forms in the Precambrian and Mesozoic Eras?  plz help asap

anonymous · Answer

Also What happened to many life forms to mark the end of each era and begin a new one? plz help

anonymous · Answer

http://teacher.scholastic.com/scholasticnews/indepth/upfront/grolier/Earth_History.htm

anonymous · Answer

The end of each era is marked by a major change in types of dominant species living on earth.  Many, probably most of these changes were caused by massive extinction events wiping out one type of fauna and making way for others to evolve and radiate.  Extinctions happened for several reasons, volcanic activity and climate change were fairly common reasons.