a principle that geologic processes that occurred in the past can be explained by current geologic processes.
the age of an object in relation to the ages of other objects.
Law of Superposition
the law that a sedimentary rock layer is older than the layers above it and younger than the layers below it if the layers are not disturbed.
a break in the geologic record created when rock layers are eroded or when sediment is not deposited for a long period of time.
Law of Crosscutting Relationships
the principle that a fault or body of rock is younger than any other body of rock that it cuts through.
the numeric age of an object or event, often stated in years before the present, as established by an absolute-dating process, such as radiometric dating.
a banded layer of sand and silt that is deposited annually in a lake, especially near ice sheets or glaciers, and that can be used to determine absolute age.
a method of determining the absolute age of an object by comparing the relative percentages of a radioactive (parent) isotope and a stable (daughter) isotope.
the time required for half of a sample of a radioactive isotope to break down by radioactive decay to form a daughter isotope.