EES - Fossil formation and stratigraphy (MOD5T4)

5.4.1 - Investigate and model processes of fossil formation by examining a variety of methods in rock, including: mould formations, cast formations, trace fossils 5.4.2. - Discuss the significance of index fossils in generating a geological timescale 5.4.3. - Extrapolate how the principles of uniformitarianism and superpositions as well as fossils and absolute dating can be used to date events of geological significance

Fossil

Remains and traces of once living organisms that have been preserved in sedimentary rock

Conditions for fossilisation

- quick burial

- suitable body parts

- little geological disturbance

Mould fossil

fossil formed when an organism decomposes underneath sediment, leaving a hollow shape

Internal mould

Impressions of the organism's interior surface

External mould

Impressions of the organism's exterior surface

Cast fossil

forms when a mould is filled with sediment

Carbon film fossil

fossil formed in an extremely thin coating of carbon on a rock

Trace fossil

fossil remains that record activity (e.g. footprints, tracks etc.)

Preserved remains

organisms preserved in an unaltered state (usually in ice, amber, tar and peat bogs)

Replacement fossils

organism's organic material is replaced by minerals in water

Permineralised fossils

minerals fill in a mould or voids left by the organism being dissolved over time. Minerals fill the spaces with organic tissue.

Original hard parts

Unalterd skeletal remains

Index fossils

fossils that are useful for dating and correlating the strata in which it is found

Relative dating

method of determining the age of a fossil by comparing its placement with that of fossils in other layers of rock

Absolute dating

technique used to determine the actual age of a fossil

Uniformitarianism

geological processes that occurred in the past can be explained by current geological processes

Superposition

younger rocks lie above older rocks if the layers have not been disturbed