Paleozoic

The Paleozoic Era is the first of three major time periods called geological eras in the Phanerozoic Eon. It began about 538.8 million years ago and ended 251.9 million years ago. The Paleozoic is split into six smaller time periods called geologic periods: the Cambrian, Ordovician, Silurian, Devonian, Carboniferous, and Permian.

The name "Paleozoic" comes from the Greek words for "ancient life." During this time, Earth saw many big changes in its land, climate, and the kinds of life that lived there. One of the most exciting moments was the Cambrian explosion, when many new kinds of animals appeared very quickly. Animals such as arthropods, molluscs, fish, amphibians, reptiles, and synapsids all evolved during the Paleozoic.

Life first began in the oceans but later moved onto land. By the end of the Paleozoic, large forests of early plants grew across the continents. These plants eventually became the coal deposits found in Europe and eastern North America. The Paleozoic Era ended with a huge event called the Permian–Triassic extinction event, which was the largest loss of life in Earth's history. It took a long time for life to recover after this event.

Boundaries

The Paleozoic Era begins a big change in Earth's history. It marks when complex life first appeared in the rocks. Scientists decided that the start of the Paleozoic is shown by special marks left by ancient animals, called trace fossils. These marks help us match rock layers from different places around the world.

The end of the Paleozoic is marked by the first appearance of a certain type of tiny sea creature. This change happened about 251.9 million years ago and shows when Earth started to recover after a major event that changed the planet.

Geology

The Paleozoic Era began about 538.8 million years ago and ended 251.9 million years ago. During this time, big changes happened on Earth. At the start, a huge landmass called Pannotia broke apart, and later another giant landmass called Pangaea began to form.

The Paleozoic Era had six main time periods. The first was the Cambrian, when many new kinds of sea creatures appeared, like simple plants and early animals. Next came the Ordovician, when more sea animals evolved, and some began to move onto land. The Silurian saw life recover and more fish appear in the oceans. The Devonian is known for many kinds of fish and the first plants growing on land. The Carboniferous had lots of trees and swamps, and the first animals that could lay eggs on land appeared. Finally, the Permian ended with all the continents joining into Pangaea, and many plants and animals appeared, but a big event caused most life on Earth to disappear.

Cambrian Period

Main article: Cambrian

Ordovician Period

Main article: Ordovician

Silurian Period

Main article: Silurian

Devonian Period

Main article: Devonian

Carboniferous Period

Main article: Carboniferous

Permian Period

Main article: Permian

Climate

The early part of the Cambrian period had moderate weather, which became warmer as sea levels rose. However, the landmass called Gondwana moved south, placing parts of Africa and South America near the South Pole by the Ordovician period.

During the early Paleozoic, the climate varied greatly by location. Some areas were warm and tropical, like parts of Northern Europe, eastern North America, and Greenland, while others, such as China and Australia, had cooler waters. The Ordovician and Silurian periods were generally warm, with high sea levels, interrupted briefly by a cooler period ending in a glaciation about 445 million years ago. This cold period caused a major loss of many plant and animal species.

The middle Paleozoic was relatively stable. Sea levels rose again during the Silurian and Devonian periods. The joining of landmasses created new warm, shallow seas. As plants grew along continents, oxygen in the air increased while carbon dioxide decreased. The Devonian period ended with some changes in animal life, but overall species numbers stayed about the same.

The later Paleozoic had many uncertainties. The early Carboniferous period saw oxygen levels rise and carbon dioxide fall sharply, leading to colder periods. Though these were colder than the Late Ordovician ice age, they did not greatly affect living things. By the Cisuralian time, oxygen and carbon dioxide levels returned to normal. The formation of the supercontinent Pangaea created large dry areas with extreme temperatures. The Lopingian period brought falling sea levels, more carbon dioxide, and worsening climate conditions, leading to a major loss of many species at the end of the Paleozoic.

Flora

Plants first appeared in water during the Paleozoic Era and later started to grow on land around 420 million years ago in the Silurian Period. The most lush plant life grew in the Carboniferous Period, with huge forests covering the land. However, changes in the weather caused these forests to shrink, reducing plant variety in the following years.

Fauna

The Paleozoic Era saw many different kinds of animal life begin. At the start of the Cambrian Period, many animal groups appeared suddenly in the oceans. The first fish appeared during this time and became more diverse later on.

Some fish developed special features that allowed them to move onto land. By the late Devonian Period, some fish could crawl on land using strong fins. These fins later evolved into legs, and these animals became the first four-legged creatures, known as tetrapods. Amphibians were common on land until changes in the climate affected their numbers, allowing other animals to become more widespread. These new animals split into different groups, with some becoming very successful and diverse through the Permian Period.

Microbiota

During the Paleozoic Era, tiny plants called phytoplankton lived in the oceans. These plants did not have many nutrients and were used to surviving in conditions where nutrients were scarce. Because of this, the Paleozoic Era had relatively few different kinds of life compared to later times.