Geology Time Flashcards
“Distinguish between numerical (absolute) and relative dating?”
Relative dating tells how old something is in relation to other objects, absolute dating provides a specific calendar year for the occupation of a site.
“What is the law of superstition?”
older sedimentary rock layers lie beneath younger sedimentary rock
“When you observe an outcrop of steeply inclined sedimentary layers, what principle allows you to assume that the beds were tilted after they were deposited?”
Angular unconformity
“Distinguish among angular unconformity, disconformity, and nonconformity.”
Angular unconformity- tilted rocks are overlain by flat-lying rocks
Disconformity- strata on either side of the unconformity are parallel
Nonconformity- metamorphic or igneous rocks in contact with sedimentary strata
“List and briefly describe five different types of fossils.”
- The remains of relatively recent organisms
-Entire animals, flesh included
-Remains are petrified (turned into stone)
-Molds and Casts
-Carbonization
List two conditions that improve an organism’s chances of be preserved as a fossil.
-Rapid burial
-Possession of hard parts
Why are fossils such useful tools in correlation?
The content of a fossil can determine a time period which can help with correlation.
Why is Radiometric dating the most reliable method of dating the geological past?
it is a complex procedure that requires precise measurement
To provide a reliable radiometric date, a mineral must remain in a closed system from the time of its formation until present. Why is this true?
a mineral in an open system may be prone to weathering and can cause problems in the accuracy.
What precautions are taken to ensure reliable radiometric dates?
a closed system
only fresh unweathered rock samples are used
What subdivisions make up the geological time scale?
Era, Phanerozoic eon, periods, epochs
Briefly describe the difficulties in assigning numerical dates to layers of sedimentary rock.
so rocks are not the same age as the rock in which they were formed
What is correlation?
Matching of rocks of similar ages in different regions
Isotopes Used
Uranium, Thorium, Rubidium, Lead,
Why’s is precambrian time important?
Laid down over millions of years, these rock layers contain a permanent record of the Earth’s past, including the fossilized remains of plants and animals buried when the sediments were formed.
