The Paleozoic era - (544 to 245 million years ago) contained to of the most important events in the history of animal life.  In the beginning, it saw unprecedented growth in animal phyla.  At the end, it saw the largest mast extinction in history that wiped out 90% of marine animals.

540-500 million years ago - The Cambrian Period, often referred to as the "Cambrian explosion", is known as the time when most major groups of animals appear on the fossil record for the very first time.

505-440 million years ago - The Ordovician Period is known as the time when plants may have invaded last for the first time.  This period is also known for when all the regions north of the tropics were covered in water and the solitary land mass (known as Gondwana) shifted to the south pole causing glaciers to for which lowered the water table and let the way for the mass extinction of 60% of all marine life.

440-410 million years ago - The Silurian Period saw the stabilization of the earth's climate and the substantial evolution of fishes.   There was a wide and rapid spread of jawless fishes along with the first freshwater fishes and even fishes with jaws.  Coral reefs made their first appearance.  The discovery of fossils containing relatives of spiders, centipedes and vascular plants provided good evidence that life on land was also being sustained.   

410-360 million years ago - The Devonian Period gave way to the first trees and forests.  The two major animal groups on land were the Tetrapods or land living vertebrates and the first Arthropods including insects.  At this time there were three continental landmasses.  North America and Europe were in the middle still submerged by water while to the north was modern day Siberia and South America, Africa, India and Australia were all south of the equator.

360-286 million years ago - The Carboniferous Period was named because of the rich coal deposits that occurred in modern day Europe, Asia and North America.  The greatest evolutionary innovation in animals was the amniotes egg, which enabled the ancestors of birds, mammals and reptiles to reproduce on land.  The continents of Gondwana (modern day Europe and North America) and Laurussia (modern day South America and Africa) collided causing the formation of the Appalachian mountain range in North America and the Hercynian range in the United Kingdom.

286-245 million year ago - The Permian Period is known for the greatest mass extinction of animal life in history.  With most invertebrates dying off, the marine communities were the hardest hit.  The species that did survive never regained their dominance.  On land, the extinction of the diapsids and synapids cleared the way for the dinosaurs.  Great forests containing ferns gave way to new species called gymnosperms, which enclosed its offspring in a seed.  The three Land masses had fused together into one super continent known as Pangea that stretched from the north to south poles.  The interior of this super continent was dryer and did not receive much precipitation.  The rest of the earth was one big ocean called Panthalassa.