geolical time Flashcards
what is relative dating?
put things in order without knowing the exact order
what are the stratigraphic principals?
principle of superposition
principle of original horizontality
principle of original lateral continuity
principle of cross cutting relationships
principle of inclusion
principle of unconformity
principle of faunal succession (evolution)
what is the principle of superposition
because of gravity, oldest sediments are on the bottom
what is principle original horizontality
sediment has been deposited in horizontal layers can be deformed into folds or broken by faults
what is principle of original lateral continuity?
you can trace undeformed layers from one rock outcrop to another even when some of the layers have been eroded
what is the principle of cross cutting relationships?
a geologic feature that cuts across another is younger than the feature it cute across
what is the principle of inclusion?
a rock inclusion is older than its host
what is the principle of unconformity?
rocks above an unconformity are younger than the rocks below
what is an unconformity?
an erosional surface where time is missing from the rock record
what is the principle of faunal succession?
an extinct organism will only be found in rocks formed when the organism was alive, therefore fossils appear in a predictable order
what is absolute dating?
calculating a numerical date
what does number of protons determine?
what element something is
what is an isotope?
atoms with different number of neutrons but the same number of protons
what is a stable isotope?
dont spontaneously break down
what is a radioactive isotope?
breakdown into daughter isotopes over time
what is the rate of decay?
how quickly something breaks down
how is rate of decay measured?
by half-life, the amount of time it takes for half the sample to break down
what is radiometric dating?
calculate the age of a sample (must know half-life and parent to daughter ratio)
what happens if an isotope decays too fast?
no parent left, cant keep track of time
what happens if an isotope decays too slow?
not enough daughter present to measure reliably
what does radiometric dating of igneous rocks measure?
the age of crystallization
what does radiometric dating of metamorphic rock meausrre?
age of metamorphism
what does radiometric dating of sedimentary rock measure?
the age of formation of crystals in the rock not the rock itself
what is the geologic time scale?
a summary of earths history
how is geologic time split?
into large units of time called eons
how are eons split?
eras, periods, epochs
how are the boundaries of units defined?
by the appearance or extinction of an animal or groups of animals
how are the absolute ages determined?
through radiometric dating
what happens the farther back you go in time?
the more different animals will look until there are no animals at all
why dont we know more about earths history?
subduction recycles rocks so they are rare
evidence has been destroyed
