Kinds of Fossilization

Body Fossilization

• Body fossilization occurs when remnants from the body are fossilized. Although the term implies the whole body, in reality it refers to only the hard parts of the body, such as bone or teeth because soft tissues tend to decompose rapidly. Body fossils are the stereotypical representation of a fossil in most people's minds and are often displayed in museums.

Petrification

• Petrified fossils are another type of fossil which are often mistaken for bone. These fossils occur in different sizes and although they might appear to be bone, they are actually minerals that gradually replaced the remains of the life form.

  Petrification usually occurs when a life form is buried under sediment, preventing oxygen from reaching it. Because oxygen is largely responsible for natural decomposition, lack of it slows the process. Over time, water seeps through the soil, reaching the remains. Over thousands of years, the minerals from the water replace the remains, often with significant detail.

Molds &Trace Fossils

• A mold consists of a hollow imprint of what once decayed in that location. Like petrified fossils, they generally occur when a life form is buried under a layer of sediment. In this case, the animal decays, leaving a hollow impression.

  Trace fossils offer indirect evidence of an animal or plant's existence. This might come in the form of nests, feces or tracks. Most trace fossils tend to be in mold or petrified form.

True Form

• Perhaps the most interesting type of fossil is the true form fossil, where a life form is preserved exactly as it once existed -- including the soft tissues. As might be predicted, true form fossils are extremely rare and tend to only occur in ice regions, where an animal becomes frozen in ice, such as the Woolly Mammoth found completely intact in Siberia in 2005. Exceptions also include small insects trapped within sap or resins, which may also become preserved intact.