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Arches National Park Geology Tour provides an extensive, visually rich description of the geology of Arches, by Deborah Ragland, Ph.D. See our DVD collection.

Happenings During the Paleozoic Era (545-248 Million Years Ago)

Time:

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.

Last modified June 1, 2005 by Lisa Gardiner.

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The Fall 2010 issue of The Earth Scientist, focuses on rocks and minerals, including articles on minerals and mining, the use of minerals in society, and rare earth minerals, and includes 3 posters!

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