Fossils & Fossil Dating

Fossils Any remains or trace of an organism that has been preserved for a very long period of time in Earth’s crust. Paleontologists study and research fossils Fossils can be footprints, bones etc.

Sedimentary Rock Usually found in sedimentary rock Process: 1. Accumulation of solid particles (sediments-sand, silt, clay) 2. compress & harden (sedimentary rock)

Fossil Types(fig. 10.27,p. 321) Petrified Fossils: remains of organisms that harden during fossilization, becoming hard as rock.

2. Cast (or Mould )Fossils: sedimentary rock takes the shape of the organism’s remains which later decompose to become moulds or was later filled in by minerals (cast)

3. Body Fossils: form when organisms become trapped in matter that prevents them from decomposing & preserving the entire body.

4. Trace Fossils: traces left in soft soil by an organism.

Stratigraphic layer a stratum(layer) of sedimentary rock that formed in the same time period as the rock

Stratigraphic Principles Law of Original Continuity all sedimentary rock contained in a single stratigraphic layer formed in the same time period Law of Superposition the deeper a stratigraphic layer is in the ground, the older it is These laws apply to fossils

Relative Dating A method that helps establish the order in which the fossils formed, without identifying their absolute age. (compares two fossils in same layer)

When principles are applied then: 1. Fossils in same layer, formed in same period 2. Older fossils buried deeper than more recent fossils

Absolute Dating Method used to determine the age of fossils in years Ex. 1. Counting growth rings in trees 2. Radioactive decay of Carbon-14