Fossils

Fossil

The preserved remains or traces of an organism that lived in the past

sedimentary rock

a rock that forms from compressed or cemented layers of sediment

relative age

The age of a rock compared to the ages of other rocks

absolute age

the number of years since the rock formed

geologic column

the sequence of fossil-containing rock layers that shows the supposed record of the history of life on the earth

radioactive decay

when the atoms of an unstable isotope break down to form atoms of another stable isoptope

half-life

length of time required for half of the radioactive atoms in a sample to decay

radiometric dating

method used to determine the age of rocks using the rate of decay of radioactive isotopes

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

igneous rock

rock that forms when magma or lava cools and solidifies

Geologic Time Scale (GTS)

the categories of time into which Earth's history is usually divided by geologists and paleontologists: eons, eras, periods, epochs

fossil record

The information provided by fossils about the earths history

Extinction

A term that typically describes a species that no longer has any known living individuals.

Mass Extinction

Event in witch many types of living things become extinct at the same time