Paleozoic Era

The Paleozoic Era is known as “Ancient Life”. The Paleozoic Era is divided into six different periods. During this time, many major events that occurred led to the development of new organisms. Changes in the environment, climate, and the surface of the Earth led to the evolution of new organisms.

A lot of new complex organism evolved during the Cambrian period.  It is known as the “Cambrian Explosion”. Recall that the majority of the Earth was covered by warm and shallow oceans.  A diversity of marine animals began to evolve and thrive in the oceans.  The trilobite is the most common invertebrate fossil found in sedimentary rocks.  Trilobites are also used as index fossils to determine the age of Cambrian rocks.  Brachiopods were also abundant during the Paleozoic era. They were a type of marine invertebrates that look like clams or oysters. Worms, jellyfish, sponges, and snails are invertebrates that existed during the Cambrian period.

As the population of brachiopods increased, the population of trilobites decreased during the Ordovician period.  Primitive vertebrates also emerged.  Bony plated fish without teeth or jaws were the oldest type of Ordovician vertebrates.  Changes in the Earth’s geological appearance were also taking place during the Ordovician period.  Tectonic activity or the movement of landmasses led to formation of two micro-continents, Gondwana and Laurentia.  Geologists believe that Africa portion of Gondwana was covered with glacial ice because of its location near the South Pole.   Scientists believe an ice age led to a mass extinction at the end of the Ordovician period.

The first plants and animals appeared on land during the Silurian period.  Mosses and ferns were the first types of plants to evolve.  Scorpion-like creatures called eurypterids lived in shallow waters and could grow up to 3 meters long. They were developing jaws which helped improve their feeding options.  The types of creatures that dwell on land were primitive arthropods.  Changes were occurring amongst the primitive fish.

The Devonian period is known as the “Age of Fishes” because fossils of a variety of fishes were found in rocks.  Scientist believed one type of fish had bony fins that allowed it to crawl on land.  Another kind of fish had lungs so it was probably able to breathe air. Adaptations such as roots and vascular tissue allow plants to move onto land. Land plants probably evolved from algae.  Photosynthetic land plants removed carbon dioxide from atmosphere and when combined with water and sunlight produce oxygen and glucose.  By products of land plants provide oxygen and food (glucose) for animal to move onto the land. Ancestors of amphibians such as frogs, toads, and salamanders evolved and were able to flourish on land.  A mass extinction also occurred at the end of the Devonian period.  Jawless fish and the fish with bony plates did not survive this period.  The continents were continuing to move and collide.  This led to the formation of mountains and climate changes.  The North America landmass joined with present-day Europe and parts of Asia to form the supercontinent Laurasia.  Although Gondwana was most likely still positioned near the South Pole; Laurasia was located near the equator and its inhabitants experienced tropical climate conditions.

The Carboniferous period is named for the “coal bearing” swamps and forests that covered most of the land.  Large amounts of coal deposits developed in wet and tropical climate. The Carboniferous period is divided into the Mississippian and Pennsylvanian periods.  The movement along plate boundaries led to the formation of the Appalachian Mountains.  Insects and the earliest reptiles resembling lizards also evolved.

The last period in the Paleozoic Era is called the Permian period.  Plate tectonic activity pushed all of Earth’s landmasses together to form the supercontinent Pangaea.

Changes in the environment and climate when the continents joined together affected animals so much that over 90% of all the species became extinct.  This was the largest mass extinction in Earth’s history.  One theory states that the majority of organisms were not able to adapt to the rapid changes in temperature.  The summers were very hot and the winters were very cold. Coastal boundaries that were once bordering the ocean were now next to another landmass.  This led to the development of deserts and many marine animals died because their coastline did not exist anymore.  Another theory suggests that volcanic eruptions released debris and gases into the atmosphere to block out the sun. This affected the food chain because photosynthesizing plants were not able to provide nourishment for other animals.