Ch. 17 Quiz
concurrent range zones
established by plotting the overlapping ranges of two/more fossils with different geologic ranges
guide fossil
fossil used in the con-current range by charts
fossil succession
fossils at the bottom are older
inclusions
fragments of one rock in a layer of another are older than the rock layer itself
easily identified, widespread, short geologic range
guide fossils meet three criteria:
fossils and the principle of fossil succession
how do geologists correlate rock units over large areas
use decay rates of unstable isotopes
how do geologists use radiometric dating to determine the absolute age of rocks?
cross cutting relationships
igneous intrusion/fault, younger than the rocks it cuts through
angular unconformity
layers above and below unconformity have different orientation
disconformity
layers above and below unconformity have the same orientation
stratigraphy
mapping of the rock layers, focuses on composition, origin, age relationships, geographic extent
lithostratigraphic correlation
matches up the same rock units over a larger area with no regard for time
relative
placing events in order by their position in the geologic record, doesn't say how long ago an event took place just that one event came before another
absolute
provides specific dates for events expressed in years, radiometric dating
lateral continuity
sediment extends laterally until it thins or ends along basin edges
original horizontality
sediment is deposited in horizontal layers
superposition
sedimentary rock layers have oldest on bottom, youngest on top
unconformities
sequences of strata, represent times of non deposition, gap in geologic record, incomplete rock record
no, isotopes are too short lived
could geologists use radiocarbon dating to date very old rocks?
nonconformity
cut into metamorphic or igneous rock and covered by sedimentary
lithostratigraphic unit and biostratigraphic unit
defined by content
time stratigraphic correlation
demonstrates time equivalence of events, can use fossils to show time equivalence
uniformitarianism
the same processes seen today have operated over vast amounts of time, can't interpret the rock record without this principle
time-stratigraphic unit and time unit
those expressing/related to geologic times
igneous and metamorphic
which types of rocks can be radiometrically dated?
rock layers don't extend indefinitely
why can't geologists rely on lithostratigraphic correlation to demonstrate time equivalence when mapping large areas?
