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?

The Paleozoic era that spanned from about 542 million years ago to 250 million years ago is considered as the time of enormous modifications on Earth. The era started with the split of one supercontinent and the production of another. The plants became global, and the initial vertebrate species started colonizing the lands.  

The Cambrian period is the initial period of the era and is also known as the age of Tribolites. The explosions of life in the oceans started during this time. The majority of the continents were covered in shallow and warm seas. The dominant invertebrates during this time were tribolites. Fish started emerging during this time, which later led to the emergence of amphibians.