The Paleozoic Era is the second earliest era out of four. The climate in the beginning of the Paleozoic Era was moderate but unstable. The climate soon after started switching from stable to unstable. After that, the climate started to get super cold. The cold climate started another ice age. Again, the carbon dioxide levels rose some more. The continents formed a U shape with continents inside of it. The big U shape stretches from north to south and east to west covering almost the whole world except for some of the space in the middle with a few smaller islands. That is what the world looked like in the Paleozoic Era. As for life in the the Paleozoic Era, plants and invertebrates thrived. Plant life started to take over the earth. Over 900 species of invertebrate animals were recorded by scientists. At this time there were both marine and land animals but all of them were invertebrates. Animals thrived just until the largest mass extinction on Earth happened. 96% of marine animals died during this and 70% of land animals died. Mammal-like reptiles evolved too. After so many animals evolved, the world’s largest mass extinction took place.