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The Paleozoic Era started 543 MYA and ended 248 MYA. It’s nickname is “Age of Invertebrates.” Paleozoic means “ancient life.” Oxygen levels reached new heights in a warm and stable climate. It was warm worldwide. An ice age followed the warm climate. That meant the sea-level went downward because the water froze to become ice. 450 MYA: there was a long strip of land at the bottom of the Earth, also, there was three big islands just below the equator. 400 MYA: The long strip shortens and the islands move above the equator. Also 400 MYA: two of the islands collide to form a big island. 300 MYA: everything collides to form a supercontinent in the middle of the Earth. Also 300 MYA: the Earth freezes at the bottom. The tectonic plates move and form mountains. Gondwana (southern hemisphere’s primary landmass) forms 500 MYA. The Cambrian Explosion of life occurs. Hard-shelled animals evolve. 535 MYA Chordates (animals with tails, gills,cartilage, and no bones) evolve. Marine reefs emerge 530 MYA. Cambrian Extinction happened 520 MYA and killed reef-builders and other shallow water organisms. It ended the Cambrian Explosion and sea-levels changed and there was oxygen depletion.
See Below: Paleozoic Era Climate