KEY CONCEPT Specific environmental conditions are necessary in order for fossils to form.

Introduction… no notes from this slide… Specific conditions are needed for fossilization. Only a tiny percentage of living things became fossils.

Fossils can form in several ways. Permineralization: occurs when minerals in H2O are deposited around or replace the hard structure

Natural cast: forms when flowing water removes all of the original tissue, leaving an impression that minerals then fill in

Trace fossils: record the activity of an organism

Preserved remains: form when an entire organism becomes encased in material such as ice

Worth mentioning but you don’t have to write this down… Amber-preserved fossils are organisms that become trapped in tree resin that hardens after the tree is buried.

Relative dating: Estimates the time during which an organism lived by comparing the placement of the fossil in rock with the placement in other layers of rock

More on relative dating… no notes to take here… Relative dating estimates the time during which an organism lived. It compares the placement of fossils in layers of rock. Scientists infer the order in which species existed.

Radiometric dating: Technique that uses the natural decay rate of unstable isotopes found in materials in order to calculate the age of the material Isotopes: Atoms of an element that differ in their number of neutrons. neutrons protrons

Radiometric dating Half-life: The amount of time it takes for half of the isotope to decay. (copy curve onto graph in your notes)