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History of Mesozoic Life

Life diversified during the Mesozoic, including the dinosaurs,until the mass extinction that came from a giant asteroid impact.

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The Petrified Forest

The Petrified Forest

Credit: Jon Sullivan
Source: http://en.wikipedia.org/wiki/File:PetrifiedWood.jpg
License: CC BY-NC 3.0

Credit: S. W. Williston
Source: http://en.wikipedia.org/wiki/File:Mystriosuchus.jpg
License: CC BY-NC 3.0

Petrified Forest National Park in Arizona is one of the best places to see petrified wood. Other fossils include a crocodile-like reptile, a phytosaur (seen above). A lot can be learned about the environment 225 million years ago when these rocks were deposited.

Amazing But True!

  • Rock layers in Petrified Forest National Park are Upper Triassic shales and siltstones of the Chinle Formation.
  • Volcanic eruptions deposited silica-rich ash.
  • Downed trees accumulated in river channels. The trees were buried by sediment including the silica-rich volcanic ash.
  • Groundwater dissolved silica from ash and carried it into logs. Quartz crystals replaced the organic material. This is permineralization.
  • At least nine species of fossil trees are found in the park. All are extinct.
  • Other fossils were created by other processes including compression. Among the many fossils are ferns, cycads, ginkgoes, snails, clams, giant reptiles called phytosaurs, large salamander-like amphibians Buettneria and early dinosaurs.
  • The sediments and fossils were buried, and then re-exposed during 35 million years of uplift and erosion.

Explore More

With the links below, learn more about The Petrified Forest, Arizona. Then answer the following questions.

  1. What was the environment of northeastern Arizona like when the Chinle Formation was deposited?
  2. Why is it important that the logs were buried by sediment before permineralization?
  3. Why are the petrified logs so colorful?
  4. What processes led to the petrified logs just sitting on the ground?

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Image Attributions

  1. [1]^ Credit: Jon Sullivan; Source: http://en.wikipedia.org/wiki/File:PetrifiedWood.jpg; License: CC BY-NC 3.0
  2. [2]^ Credit: S. W. Williston; Source: http://en.wikipedia.org/wiki/File:Mystriosuchus.jpg; License: CC BY-NC 3.0

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