GEOLOGY

Detailed explanation-1: -Life was primitive during the Paleozoic and included many invertebrates (animals without backbones) and the earliest fish and amphibians.

Detailed explanation-2: -Abundant oxygen probably encouraged evolution, especially on land. Giant insects took to the air. Vertebrates moved to land; amphibians were far larger, more abundant, and more diverse than today. The shelled (water-tight) egg allowed early reptiles to reproduce on land without drying out the embryo.

Detailed explanation-3: -During the Paleozoic Era (541 to 252 million years ago) Fish diversified and marine organisms were very abundant during the Paleozoic. Common Paleozoic fossils include trilobites and cephalopods such as squid, as well as insects and ferns. The greatest mass extinction in Earth’s history ended this era.

Detailed explanation-4: -During the Paleozoic Era (541 to 251.9 million years ago), fish diversified and marine organisms were very abundant. In North America, the Paleozoic is characterized by multiple advances and retreats of shallow seas and repeated continental collisions that formed the Appalachian Mountains.