Uniformitarianism: the processes that act on the Earth’s surface today are the same as the processes that have acted on the Earth’s surface in the past

James Hutton

“The present is the key to the past”

age of anything compared to the age of something else

•doesn’t indicate actual date of occurrence

law of superposition: in undisturbed rock, the older rocks will be at the bottom and the youngest rocks will be at the top

law of cross-cutting relationships:an igneous rock cutting through another rock is younger than the rock it has cut-cross

law of included fragments: pieces of one rock found in another rock must be older than the rock in which they are found

Contorted rock, hard to determine relative age (Copiapo, Chile)

unconformity:break in the geologic rock record

•nonconformity: when stratified rock rests upon unstratified rock

Noncomformity1.Granite formed2. Granite exposed by erosion 3. Beds 1-3 deposited

•angular unconformity: boundary between horizontal and tilted layers of rock

Angular Unconformity1.Beds 1-6 deposited2. Beds 1-6 tilted3. Erosion 4. Beds 9,10 deposited

•disconformity:boundary between layers of rock that have not been deposited continuously

Disconformity1.Beds 1,2 deposited2. Erosion3. Beds 5, 6, 7 deposited