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Petrification Of Fossils

"Fossil" is a broad term referring to any remnants of life preserved from ancient times, whether of an actual living creature or even just its tracks. Fossilization can occur through several different processes, two of which are referred to as "petrification" because they result in a stone fossil of the original organism.

Process of Fossilization
- When a living creature dies, it normally decays and leaves nothing behind. Sometimes, a combination of events occurs that can turn the creature into a fossil. If scavengers don't eat the remains and something causes them to be buried soon after death, the hard parts of the body can be preserved. For example, if a dinosaur was killed by a mudslide and completely buried under the mud, scavengers wouldn't have a chance to get to it and it could be turned into a fossil over time.
Replacement
- Replacement is a type of petrification in which water eats away the creature's body over time, but does so very slowly so that it leaves small amounts of minerals in place of the creature's bones or other hard parts. Because the process happens so gradually and the minerals build up little by little over a very long time, they replace the creature's bones and leave mineral deposits in the exact same shape. The minerals build up into a copy of the creature's shell or skeleton made out of stone.
Permineralization
- The other type of petrification is called permineralization. Unlike the replacement process, which literally wears away the bones of the creature and replaces them with rock, the permineralization process works through infiltration. Water containing mineral deposits seeps into cracks or pores in the creature's remains, gradually building up into a stone fossil. This type of fossil contains some of the original organic material mixed with the stone. Permineralization can petrify trees and plants as well as bones and teeth.
The Petrified Forest
- Arizona's Petrified Forest National Park contains the remains of a forest that was fossilized through petrification. The Petrified Forest was alive in the late Triassic period, 200 million years in the past. It contains fossilized trees up to 190 feet long, as well as the fossilized remains of teeth and other traces of animal life. The fossilized trees in the Petrified Forest were created when fallen logs were washed up in the mud on the sides of a river in Triassic times, and the water from the river fossilized them through the permineralization process.

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