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

absolute age: identifies actual age of a rock layer

•if actual time of two events is known, the length of time between two events can be calculated

fossil: remains or evidence of living things

(1) original remains: the actual, unchanged remains of the organism are preserved

(a) frozen in ice

(b) preserved in amber(tree sap that has hardened

(c) mummification

(2) replaced remains: soft parts of the organism have disappeared and been replaced by minerals

petrification

(3) molds and casts of the original organism(4) trace fossils: evidence of life other than remains of an organisms activities and/or appearance

(a) footprints

(b) imprint

(c) tracks, trails, burrows, borings

coprolites: fossilized dung or waste materials from ancient animals

T-Rex Carnivore Coprolite (8 lbs.)

gastroliths: fossilized stone found within the digestive system of a dinosaur or other reptile

index fossil: fossils found exclusively in rock record of a particular geologic age•must have (4) characteristics:(1) must be easily recognizable(2) must be widespread in occurrence(3) must be limited in time(4) must be found in large numbers with the rock layer

geologic time scale: summary of major events of the Earth’s history preserved in the rock record•the history of the Earth is divided by major changes in the Earth’s surface, climate and/or species

Eras: largest segment of time(1) Precambrian(2) Paleozoic- “ancient life”(3) Mesozoic- “middle life”(4) Cenozoic- “recent life”Eras are divided into Periods, Periods are divided into Epochs

theory of evolution: theory that organisms change over time and new organisms are derived from ancestral types•theory proposed by Charles Darwin