a principle that states that the same geologic processes shaping the Earth today have been at work throughout Earth's history
a principle that states that all geologic change occurs suddenly
determining whether an object or event is older or younger than other objects or events
a principle that states that younger rocks lie above older rocks in undisturbed sequences
an ideal sequence of rock layers that contain all the known fossils and rock formations on Earth arranged from oldest to youngest.
a surface that represents a missing part of the geologic column
the process of establishing the age of an object such as a fossil or rock layer, by determining the number of years it has existed.
atoms of the same element that have the same number of protons but have different numbers of neutrons.
a process in which radioactive isotopes tend to break down into stable isotopes of other elements.
determining the absolute age of a sample based on the ratio of parent material to daughter material
for a particular radioactive sample, the time it takes for one-half of the sample to decay
any naturally preserved evidence of life
a process in which minerals fill in pore spaces of an organism's tissue
a process in which an organism's tissue are completely replaced by minerals
any naturally preserved evidence of an animal's activity
preserved feces, or dung, from animals
a cavity in the ground or rock where a plant or animal was buried
an object created when sediment fill a mold and becomes rock
a fossil of an organism that lived during a relatively short, well-defined time span; a fossil that is used to date the rock layers in which it is found