Clues to Earths Past Fossils Remains imprints or

Clues to Earth’s Past

Fossils �Remains, imprints, or traces of prehistoric organism.

Permineralized remains �Fossils where the spaces inside are filled with minerals

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

Mold-Cast �Mold- imprint left after hard parts of organism decay �Cast- a copy of organism made from the mold

Trace Fossils �Fossils that are evidence of organisms activity (not organism itself) �Such as: � Tracks/footprints � Burrows � Trails

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

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

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

Igneous Intrusion �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.

Unconformities �Unconformities are when layers of rock are missing �Unconformities develop when running water or glaciers remove rock layers

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

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

Nonconformity �When sedimentary rock forms over eroded metamorphic or igneous rock

When the layers are too disturbed: �The same rock layers can be found in different locations; FOSSILS must be used to prove that the layers match up

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

Half-Life: Time it takes for half of the atoms in an isotope to decay

Radioactive Decay �Breaking down of an atom into a proton and an electron.

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

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