Types of Fossils

Correlation of Rock Layers

Matching rocks of similar age in different regions
Often relies upon fossils

Fossils: Evidence of Past Life

Remains or traces of prehistoric life
Types of fossils
Petrified – cavities and pores are filled with precipitated mineral matter
Formed by replacement – cell material is removed and replaced with mineral matter
Mold – shell or other structure is buried and then dissolved by underground water
Cast – hollow space of a mold is filled with mineral matter

Types of fossils
Carbonization – organic matter becomes a thin residue of carbon
Impression – replica of the fossil’s surface preserved in fine-grained sediment
Preservation in amber – hardened resin of ancient trees surrounds an organism

Types of fossils
Indirect evidence includes
Tracks
Burrows
Coprolites – fossil dung and stomach contents
Gastroliths – stomach stones used to grind food by some extinct reptiles

Conditions favoring preservation
Rapid burial
Possession of hard parts

Fossils and correlation
Principle of Fossil Succession
Fossils succeed one another in a definite and determinable order
Proposed by William Smith – late 1700s and early 1800s