Geologic Time and History PPT Flashcards
catastrophism
large scale geologic features formed in catastrophic events; the age of the earth can be measured in human historical terms; fast process over short time (ex: island formation, volcanic eruption)
uniformitarianism
earth processes can be observed to understand the past; the Earth was ancient much beyond the span of human history; slow process over wide geologic time; older than human lived (ex: sediment deposition, evolution)
stratigraphy
the science of rock layers and the processes by which they are formed (stratum is a layer of sedimentary rocks)
relative age rocks
sequence of past geologic events; age of rock, fossil, or other geologic feature relative to another feature; order of the events are analyzed but not the actual numerical age
what can complicate the relative age of rocks
dykes, faults, folds
name the four principles
original horizontality, stratigraphic superposition, lateral continuity, cross-cutting relationship
principle of original horizontality
water-laid sediments are deposited in horizontal strata (horizontal is key here)
principle of stratigraphic superposition
in undisturbed sequence of strata, each stratum is younger than the stratum below it and older than the stratum above it
principle of lateral continuity
sediments deposited in continuous layers (meaning that, if a valley cuts through a piece of land, they rocks will still stay horizontal with each other)
principle of cross cutting relationship
stratum must be older than any feature that cuts or disrupts it (dyke, fold, fault)
correlation
a method of equating the ages of strata that come from two or more different places
index fossils
fossils that lived in short period, have a wide geographic range (ex: trilobite)
fossils
remains or traces of prehistoric life; can be plants or animals; important inclusions in sediment and sedimentary rocks; important tool to interpret the geologic past; paleontology is the study of fossils; contribute to the geometric fit theory with plate tectonics
geologic time scale
a system of chronological measurement that relates stratigraphy to time (eon, ara, period, epoch)
Eons
Hadean, archean, proterozoic, phanerozoic
hadean
time between earth’s creation and age of the oldest rocks discovered
archean
roughly when single-celled life developed
proterozoic
multi-celled, soft-bodied organisms emerged
phanerozoic
the current eon where “visible life” is abundant
phanerozoic is divided into…
eras
eras
paleozoic, mesozoic, cenozoic
paleozoic
fish, amphibians, and reptiles
mesozoic
dinosaurs and flowering plants
cenozoic
birds, mammals, primates, humans
isotope
atom of the same element with the same atomic number but different mass number
stable vs. radiogenic isotopes
radiogenic isotopes: amount of element decreases with time
radioactivity
process in which an element spontaneously transforms; end product is either another isotope of the same element or into a different element (carbon14, potassium40, uranium, thorium, lead); rate of decay is constant
t-half life
time needed for half of the parent atom of a radioactive substance to decay into daughter atoms (longer half-life to date older rocks and vice versa)
to find the numerical age, scientists generally turn to…
radioactivity
