Clues to Earth’s Past

Remains, imprints, or traces of prehistoric organism.

Fossils

Fossils where the spaces inside are filled with minerals

Permineralized remains

A flim of carbon can form around an organism creating a silhouette

Carbon Film

Mold- imprint left after hard parts of organism decay

Cast- a copy of organism made from the mold

Mold-Cast

Fossils that are evidence of organisms activity (not organism itself)

Such as:Tracks/footprintsBurrowsTrails

Trace Fossils

Abundant, widespread organisms that existed for a SHORT period of time.

Index Fossils

In undisturbed layers of rock, the oldest rocks are found at the bottom, with the rocks becoming younger towards the top.

Principle of Superposition

Relative age is how old a rock or fossil is in COMPARISON to the ages of other things.

Relative Age

when an igneous intrusion cuts across a formation of rock, it can be determined that the igneous intrusion is younger than the rock it’s cutting through.

Igneous Intrusion

Unconformities are when layers of rock are missing

Unconformities develop when running water or glaciers remove rock layers

Unconformities

When rock layers are tilted and younger sediment layers are deposited horizontally on top of the eroded and tilted layers

Angular

When a layer of horizontal rock is exposed and eroded before younger rocks form over it

Disconformity

When sedimentary rock forms over eroded metamorphic or igneous rock

Nonconformity

The same rock layers can be found in different locations; FOSSILS must be used to prove that the layers match up

When the layers are too disturbed:

Calculating the absolute age of a rock by measuring the amounts of materials in a rock and knowing the material’s half life.

Absolute Dating

Half-Life: Time it takes for half of the atoms

in an isotope to decay

Breaking down of an atom into a proton and an electron.

Radioactive Decay

Uses the properties of atoms in rocks and other object to determine their ages.

Radiometric Dating

Principle that Earth’s processes occurring today are similar to those that occurred in the past.

Uniformitarianism