Fossil Formation and Dating: Petrification, Types, and Processes

Petrification / permineralization

Sequence of events that turn the remains of organisms into a cast made of stone.

Step 1 of Petrification

Animals or plants die and get covered with sediment.

Step 2 of Petrification

The soft parts are decomposed by bacteria, but hard parts remain.

Step 3 of Petrification

Sediment covering becomes compacted into rock, and water drains down through sediments bringing dissolved minerals.

Step 4 of Petrification

Dissolved minerals replace other materials in bones and hard parts but maintain the shape of the material.

Where to find fossils?

Sedimentary rock layers such as limestone, shale, and sandstone, often exposed by erosion.

How are fossils created?

Dead organisms are rapidly buried by sediment to prevent decomposition.

Ideal place for fossil formation

Bottom of a quiet area of a lake, safe from damage.

Relative dating

Determines chronological order of fossils as older or younger based on position in rock layers without a specific age.

Absolute dating

Calculates actual age in years using methods such as radiometric dating.

Crinoids

Marine invertebrates, such as starfish, sea urchins, and scallops, are characterized by circular, stacked disc-shaped columnals.

Trilobites

Extinct marine arthropods with three-lobed bodies were abundant during the Cambrian period.

Coprolites

Fossilized poop that provides evidence of prehistoric animal diets and behaviors, classified as trace fossils.

Amber

Fossilized tree sap containing preserved insects or plant matter.

Brachiopods

Preserved shells of marine invertebrates that look like clams.

Fossilized teeth

Mineralized remains of teeth from sharks, dinosaurs, or other vertebrates.

Petrified wood

Wood that has turned into stone through the process of permineralization, where minerals replace the structure.

Mold

Imprint in wet mud or sand that hardens. (into stone)

Cast

Models formed from sediment or minerals filling a mold or decomposing organism replaced by minerals. (turned into stone)