Characteristics of the Paleozoic Click on image for full size (115K JPG) L.Gardiner/Windows to the Universe (fossil images courtesy of AGI Imagebank)

Time:

• 545 to 248 million years ago
• Geologic periods (divisions) of the Paleozoic: Cambrian, Ordovician, Silurian, Devonian, Carboniferous, Permian
• (See the geologic timescale!)

Paleogeography:

• Early in the Paleozoic the continents were far apart, but, by the end, all continents had been assembled into a large supercontinent called Pangaea. Continents move due to plate tectonics.

Climate:

• Geologic evidence shows that a brief glaciation occurred 430 million years ago. It may have lasted only one or a few million years, causing an ice sheet, similar in size to the one on Antarctica today, to cover the area that is today North Africa. At the time, this part of the African continent was positioned over the South Pole.
• Climate models have been used to help understand past weather and regional climates of the supercontinent Pangaea. The models suggest that monsoons affected the subtropical east coast, which likely had a distinct wet and dry season. This hypothesis is supported by evidence preserved in the rocks formed at that time. The interior of Pangaea was likely dry, just like continental interiors typically are today.

Evolutionary Events:

• The Cambrian Explosion of Life- According to fossil evidence, almost all of the main groups of animals evolved between 530 and 520 million years ago. Most of these life forms, such as jellyfish, had no shells or bones making them difficult to preserve, so fossils are rare. However, excellent conditions in certain areas (China and Canada) led to discovery of a wealth of fossils from this time period.
• Early to Middle Paleozoic- Invertebrates (animals without backbones) ruled the seas in the early and middle parts of the Paleozoic. Diversification of animals led to a large number of different species of marine invertebrates such as corals, brachiopods, mollusks, and arthropods such as trilobites.
• Late Paleozoic- Vertebrates (animals with backbones) began to flourish in the later Paleozoic (including fish, amphibians, and reptiles). Animals and plants populated the land.
• Late Ordovician mass extinction- This was the second largest mass extinction of all time. Rapid global cooling and a million year long glaciation may have been the cause of the extinction. However, large amounts of greenhouse gases at the time mean that cooling may not have been possible.
• End-Permian mass extinction- This was the largest of all time during which as many as 96% of species in the oceans became extinct over 8 million years. This extinction may have been caused by extreme global warming as flood basalts added greenhouse gases to the atmosphere, the developing supercontinent of Pangaea, or a major drop in sea level during which the ocean level fell lower than the continental shelves providing little shallow water habitat for marine life.
  
  

Characteristics of the Paleozoic Click on image for full size (115K JPG) L.Gardiner/Windows to the Universe (fossil images courtesy of AGI Imagebank)

Time:

• 545 to 248 million years ago
• (See the geologic timescale!)

Geography:

• Early in the Paleozoic the continents were far apart, but moving tectonic plates caused continents to move together into one large continent (a supercontinent!) called Pangaea.

Climate:

• Glaciers formed 430 million years ago. They may have only lasted one or a few million years. During this time, ice covered the northern part of Africa, which was located over the South Pole.
• Climate models have been used to help understand weather and regional climates of the supercontinent Pangaea. The models suggest that monsoons affected the subtropical east coast and that interior of Pangaea was dry.
  

Evolutionary Events:

• According to fossils, a large number of animals (including the distant ancestors of many modern animals) evolved between 530 and 520 million years ago.
• Invertebrates (animals without backbones) such as corals, brachiopods, mollusks, and arthropods such as trilobites ruled the oceans in the early and middle parts of the Paleozoic.
• Vertebrates (including fish, amphibians, and reptiles) began to flourish in the later Paleozoic. Animals and plants populated the land (but many still lived in the ocean!).
• About 440 million years ago the Late Ordovician Mass Extinction occurred. It was the second largest mass extinction of all time. Over 10 million years, many marine species became extinct including those that built reefs.
• At the end of the Paleozoic, about 250 million years ago, as many as 96% of species in the oceans became extinct. They didn’t die all at once. It took over 8 million years for the mass extinction to wipe out all those species. This was the largest mass extinction of all time.
  
  
  

Characteristics of the Paleozoic Click on image for full size (115K JPG) L.Gardiner/Windows to the Universe (fossil images courtesy of AGI Imagebank)

Time:

• 545 to 248 million years ago
• (See the geologic timescale!)

Geography:

• Earth’s tectonic plates were on the move during the Paleozoic! By the end of this time they had moved so much that all of the continents were pushed together making one large continent called Pangaea.

Climate:

• 430 million years ago glaciers formed and ice covered the northern part of Africa. This area is a desert today, but back then it was located at the South Pole!
• Climate models have been used to understand the past weather patterns and climates of Pangaea. The models suggest that rainstorms called monsoons affected the East coast and that interior of continent was very dry.

Evolutionary Events:

• A large number of animals evolved between 530 and 520 million years ago including trilobites and brachiopods (pictured at left).
• During the early and middle parts of the Paleozoic, most animals lived in oceans. Animals without backbones (such as corals, brachiopods, mollusks, and trilobites) were very common.
• Animals with backbones (including fish, amphibians, and reptiles) began to flourish in the later Paleozoic. Animals and plants populated the land.
• About 250 million years ago, almost all of the species in the oceans became extinct. They didn’t die all at once. It took over 8 million years for the mass extinction to wipe them out.
• About 440 million years ago the Late Ordovician Mass Extinction was the second largest mass extinction of all time. Over 10 million years, many small marine species became extinct including those that built reefs.