Category 1
The preserved remains or traces of an organism that lived in the past.
Fossil
The age of a rock compared to the ages of other rocks.
Relative Age
When one variable is dependent on another variable.
Relative
To make a conclusion based on prior knowledge or evidence.
Infer
The study of the origin, history, and structure of Earth.
Geology
The process in which the nuclei of radioactive elements break down, releasing fast-moving particles and energy.
Radioactive Decay
The age of a rock given as the number of years since the rock formed.
Absolute Age
Length of time required for half of the radioactive atoms in a sample to decay.
Half-life
Atoms of the same element with different numbers of neutrons.
Isotope
Method of determining the age of a fossil by comparing its placement with that of fossils in other layers of rock.
Relative Dating
The geologic principle that states that in horizontal layers of sedimentary rock, each layer is older than the layer above it and younger than the layer below it.
Law of Superposition
A gap in the geologic record that shows where rock layers have been lost due to erosion.
Unconformity
Breakdown of nuclear elements into energy.
Radioactive Decay
The process of determining the age of an object using the half-life of one or more radioactive isotopes.
Radioactive Dating
Time in which half of radioactive atoms decay.
Half-life