The Paleozoic Era (paleo means "early life") lasted from about 540 to 250 million years ago. Much of what is now Colorado was dominated by two very large mountain ranges lying parallel through the state running lengthwise north to south. The mountain ranges were eroding during this time span, similar to our present Rocky Mountains, so any rocks that may have been here were washed away. In our 1000 page book, the Paleozoic would fill pages 881 through 955. Because these "pages" are missing here we need to look at rocks from other parts of the southwest to see what this area was like.

Important Events of the Paleozoic:

Carboniferous (354-290 million years ago) The first "forests" composed of large primitive trees provide a swampy habitat for early reptiles.

Devonian (417-354 million years ago) Certain fish develop the ability to crawl onto land, leading to the evolution of the first amphibians.

Silurian (443-417 million years ago) The first plants appear on land.

Ordovician (490-443 million years ago) Beginning of assembly of the supercontinent called Pangea.

Cambrian (543-490 million years ago) Evolution of all the major plant and animal phyla, including the first hard-shelled organisms.