Geologic History Flashcards
(51 cards)
geologic history
study and interpretation of earth’s past
relative age
the age of rocks or events compared to the age of other rocks or events
(ex. i am a teenager)
absolute age
the age of a rock, object, or event in years
(ex. i am 14 years old)
how do scientists determine the relative ages of rock layers
- uniformitarianism
- principle of original horizontality
- principle of superposition
uniformitarianism
the geologic processes that took place in the past are generally similar to those that take place now
principle of original horizontality
sediments are deposited in horizontal layers that are parallel to the surface they were deposited on
what do tilted or folded layers indicate
the crust has been deformed
principle of superposition
in undisturbed layers, the oldest layer is on the bottom, and each overlaying layer is younger
- does not apply if layers have been overturned or faults have forced over rock over younger rock
igneous intrusions and extrusions
as hot magma squeezes into cracks and zones of weakness, the cooling magma pastes its heat energy to the nearby rock
how to tell if this intrusion is younger or older
if its younger there will be burn marks
unconformity
a gap in the rock record caused by the burial of an eroded surface by younger sediments. shown by a wavy line
how do unconformities happen
- submergence
- deposition of sediments
- emergence
- erosion
- submergence
- deposition
where does the rock need to be eroded
above water
where does the rock need to be to be created from deposition
underwater
folding
layers of sedimentary rock that have been bent or warped by crustal forces
tilting
formally horizontal rock layers that have been tilted at an angle by crustal activity
faulting
a crack of weakness in earth’s crust along which movement occurs during an earthquake
law of cross cutting
a disruption that cuts through rock or another geologic feature must be younger than the rock or the other geologic feature
when is there contact metamorphism
when the intrusion is younger
how do you know when there is contact metamorphism
there would be dashed lines
how to know when rock layers are deposited before the fault
when the fault line goes through it
what do you know about the geologic cross-sections when the bottom layer is sedimentary
submergence is the first thing that happened
erosional surface
a surface where rock has been worn away by wind, water, or ice, often creating an unconformity
subsidence
the sinking or downward movement of the earth’s surface
