| A | B |
|---|
| James Hutton | wrote Theory of the Earth in 1788, introducing concept that later became known as uniformitarianism; suggested Earth much older than previously thought |
| uniformitarianism | principle that geologic processes occur at a constant, uniform rate and that processes at work today have been at work throughout Earth's history |
| catastrophism | principle that states that all geologic change occurs suddenly; prevailing belief during Hutton's time |
| Charles Lyell | Geologist who published Principles of Geology (1830-1833) that reintroduced concept of uniformitarianism; work influenced Charles Darwin's theory of evolution |
| modern geology | combination of theories of uniformitarianism and catastrophism; most geologic change is steady and gradual, but catastrophic events do occur, causing sudden, dramatic change |
| relative dating | determining whether object or event is older or younger than other objects or events |
| superposition | principle that states that younger rocks lie above older rocks in undisturbed rock layer sequences |
| geologic column | ideal sequence of rock layers containing all known fossils and rock formations on Earth arranged from oldest to youngest |
| fault | break in the Earth's crust along which blocks of crust slide relative to one another |
| intrusion | molten rock from Earth's interior that squeeze into existing rock and cools |
| cross-cutting rock disturbances | faults and intrusions |
| rock layer formation | geologists assumption that sediment is deposited in horizontal rock layers; if not horizontal, something must have disturbed them |
| folding | disturbance that occurs when rock layers bend and buckle from Earth's internal forces |
| tilting | occurs when internal forces cause rock layers to slant without folding |
| unconformity | surface that represents a missing part of geologic column; represents gap in geologic record; caused by non-deposition or erosion |
| 3 major categories of unconformities | disconformities, nonconformities, angular unconformities |
| disconformity | type of unconformity in which part of sequence of rock layers is missing |
| nonconformity | type of unconformity in which sedimentary rock layers lie on top of eroded surface of non-layered igneous or metamorphic rock |
| angular unconformity | type of unconformity in which horizontal rock layers lie on top of eroded tilted or folded layers |
| absolute dating | process of establishing the age of an object by determining the number of years it has existed |
| isotopes | atoms of the same element that have the same # of protons but a different # of neutrons |
| radioactive decay | process in which unstable isotopes break down into stable isotopes of other elements; occurs at steady pace |
| radiometric dating | process of determining absolute age of sample based on ratio of parent material to daughter material |
| half-life | time it takes for one-half of a radioactive sample to decay |
| types of radiometric dating | uranium-lead method; potassium-argon method; carbon-14 method |
| fossil | any naturally preserved evidence of life |
| types of fossils | fossils in rock; mineral replacement; fossils in amber; mummification; frozen fossils; fossils in tar; trace fossils |
| trace fossils | any preserved evidence of an animal's ACTIVITY (tracks, burrows, corpolites) |
| corpolites | preserved animal feces (dung) |
| index fossils | fossils of organisms that lived during a relatively short, well-defined time span; can be used to date rocks while in the field (examples: Phacops, Tropites) |
| geologic time scale | scale that divides Earth's 4.6 billion year history into distinct time intervals (divisions due to major events) |
| eon | largest division of time: Hadean eon, archaen eon, proterozoic eon, phanerozoic eon |
| era | second largest division of geologic time; eons divided into eras |
| period | third largest division of geologic time; eras divided into periods |
| epoch | 4th largest division of geologic time; sometimes periods divided into epochs |
| 3 eras of phanerozoic eon | paleozoic, mesozoic, cenozoic |
| paleozoic era | first era well represented by fossils; ended with mass extinction in which 90% of all species died; 540-248 million years ago |
| mesozoic era | known as the "age of reptiles"; dinosaurs inhabited land and water; by end of era, 50% of all species, including dinosaurs, extinct; 248-65 million years ago |
| cenozoic era | called the "age of mammals"; 65 million years ago to present |
