Biology Index
By Richard Bruce BA, MA, and PhC in Economics

A summary of on the Geologic Periods of the Paleozoic

The Paleozoic is the era, almost 300 million years, before the Mesozoic. The Mesozoic is famous for the dinosaurs.

I have had some difficulty remembering the geologic periods of Paleozoic, which makes it difficult to read the literature. So I have tried to straighten the whole thing out in my mind, and now I am writing my thinking down on this page. That way both the general public and I will be able to refer to it. This page contains relatively little in the way of new insight, I am simply organizing information.

The Paleozoic has been split into six geologic periods.

Those six geologic periods are as follows:

  1. Cambrian
  2. Ordovician
  3. Silurian
  4. Devonian
  5. Carboniferous
  6. Permian

Cambrian 541 ~ 485 Million Years Ago

The Paleozoic begins with the Cambrian, and the Cambrian begins with the Cambrian explosion. The Cambrian explosion refers to the rapid appearance of many types of life at the beginning of the Cambrian. Almost all phyla of multicellular animals appear in the geologic record at this time. For the first time organisms with hard body parts evolved, so with some exceptions, this was the beginning of the fossil record.

Ordovician 485 ~ 445 Million Years Ago

In the Ordovician primitive fish, cephalopods, and coral evolved. Squid and octopuses are cephalopods. Arthropods invaded the land. Insects, crabs, and spiders are examples of arthropods. The Ordovician ended with a massive ice age, which has been described as a snowball earth. It is considered the first mass extinction and the second most serious, so it was worse than the one that wiped out the dinosaurs.

Silurian 443 ~ 419 Million Years Ago

In the Silurian, many fish evolved, including the first jawed fish, and the first freshwater fish. Arachnids, centipedes, fungi, and vascular plants evolved on land. Vascular plants have vascular tissues allowing them to move resources around the plant and grow much larger. This was a crucial adaptation that made it possible for trees to evolve.

Devonian 419 ~ 359 Million Years Ago

The Devonian is known as the age of fish, for the first time fish, not invertebrates were the top predators in the sea. Fish moved onto land and amphibians evolved. The first trees evolved. The Devonian ended with the second mass extinction.

Carboniferous 359 ~ 299 Million Years Ago

The Carboniferous was a warm period with lots of swamps and trees. Much of our coal was formed in this period. Reptiles evolved from amphibians. The reptiles could spend their entire life on land. The period ended with a giant glaciation, ice age, centered on the south pole.

Permian 290 ~ 252 Million Years Ago

The Paleozoic ends with the Permian. The most famous animal of the Permian is probably Dimetrodon the large reptile with a sail fin on its back. In the second half of the Permian the Therapsids evolved. Therapsids were thought to be warm blooded and mammals evolved from them. The Permian ended with the third and most severe mass extinction, the great dying. The Permian is followed by the Mesozoic, a summary of which is here.

More summaries of natural history, and other biology web pages can be found in the biology index.

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Biology Index