Relative Dating & Fossils

What are the conditions necessary for the preservation of fossils?

1. Fossil should have a hard part like a shell 2. Fossil should be buried quickly 3. Low oxygen so decomposition is stopped 4. Rapid lithification of sediment 5. no scavengers

What makes an ideal index fossil?

1. must be found all over the world 2. easy to identify and recognize 3. lived for a short period of time

nonconformity

A place where an old, eroded rock surface is in contact with a newer rock layer.

Why are fossils found in sedimentary rock?

Igneous and metamorphic have undergone heat or pressure so fossils would not survive.

Law of Superposition

In undesturbed rock layers, the rock on the bottom is older than the rock on the top.

permineralization

Pore space in wood and bone filled in with materials.

Strata

Rocks - another name for rocks

index fossil

a fossil known to have lived in a particular geologic age that can be used to date the rock layer in which it is found

disconformity

a layer of horizontal rock once exposed and eroded before younger rocks formed over it

principle of inclusion

a rock body that contains inclusions of preexisting rocks is younger than the rocks which the inclusions came from

extinction

an entire species dies off and this helps explain the wide separation between the major groups of animals

mold

cavity or impression (hole) left behind when a fossil dissolves

If the sedimentary rocks are folded into a u shaped fold (syncline) the youngest rocks are in the ....

core

trace fossil

evidence of the fossil's existence is preserved (example: burrow or track)

principle of fossil succession

fossil organisms succeed one another in a definite and determinable order, and any time period can be recognized by its fossil content

principle of cross cutting relations

geologic features, such as faults and igneous intrusions are younger than the rocks they cut

What is relative age dating?

geologists used to estimate the age of things by placing geologic events in their order of occurrence

principle of faunal succession

groups of fossil plants and animals occur in the geologic record in a definite and determinable order

angular unconformity

horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers that may be either vertical or at an angle to the overlying horizontal layers

cast

if sediment fills the mold then it is possible to have a replica of the fossil in sedimentary rock

principle of superposition

in a series of stratified sedimentary rocks the lowest stratum is the oldest

replacement

minerals replace the materials of the organism (petrified wood)

metamorphic rocks in contact with layered or unmetamorphosed rocks are usually the oldest or youngest rocks in the sequence

oldest

principle of original horizontality

sedimentary layers are horizontal when originally deposited. Strata that are not horizontal have been deformed by movements of the earth's crust

law of unconformities

surfaces called unconformities represent gaps in the geologic record where layers were either not deposited for a time or it was eroded

original preservation

the organism is preserved in its whole part, fossils that have the soft and hard parts of plants and animals remains that have not undergone any kind of change since the organisms death

carbonization

the whole fossil is converted to carbon,. It occurs when an organism is buried under fine sediment. as time passes, pressure squeezes out the liquid and gaseous components and leaves behind a thin residue of carbon.

If a body of granite contains unmelted inclusions of another rock the granite rock is younger or older.

younger

an igneous rock is always (younger or older) than the rocks that it intrudes

younger

If sedimentary rocks are folded the folding is .younger or older than the youngest rock affected.......

younger than the youngest rock affected