geological time Flashcards
(27 cards)
In an unweathered sample of rock, the ratio of an unstable isotope to its stable daughter isotope is 1:15. If no daughters were present at the time the rock cooled below closure temperature, and the half-life of the isotope is 50 million years, how old is the rock?
1 billion years
An igneous dike cuts across a sequence of sedimentary beds, which is older?
the sedimentary beds
what happens after an unstable parent isotope decays?
the daughter isotope may continue to decay
Magma has intruded into some limestone, and a marble rind formed surrounding the granite pluton. The marble rind must be younger than the limestone according to the principle of…?
baked contracts
Magnetostratigraphy takes advantage of the fact that Earth’s magnetic field…?
has experienced numerous polarity reversals, with periods of normal and reversed polarity of varying lengths
can the age of earth be reliably estimated from sediment thickness?
no - much of earths history is represnted by unconformities between strata rather than the strata themselves
what principle did James Hutton put forth?
principle of uniformitarianism
if the relative ages of 2 formations are known, what else about them can be inferred?
their relative position in a sequence of rock layers
seasonal changes create layering in glaciers known as…?
rhythmic layering
in an undisturbed sequence of sedimentary rocks, younger layers overlie older layers, according to the principle of..?
superposition
if horizontal sedimentary strata overlietilted strata (and no fault is present), the surface between the horizontal and tilted strata must be an…?
angular unconformity
how much of a radioactive parent isotope will remain after 3 half lives have passed?
one eighth
In an unweathered sample of igneous rock, the ratio of an unstable isotope to its stable daughter isotope is 1:15. If no daughters were present at the time the rock cooled below closure temperature, and the half-life of the isotope is 50 million years, how old is the rock?
200 million years
which eon of geological time is represented by rocks containing an abundant shelly fossils?
phanerzoic
f the lithology and fossil content of two bodies of rock on opposite sides of a canyon are identical, then these remaining outcrops were likely physically connected at one time and formed part of an extensive, sheet-like layer of rock. This idea summarizes the principle of …
original horizontality
why is radiocarbon dating only rarely applied in geological work?
the half life of carbon-14 is so short that it can only be used to date materials that are less than 70,000 years old
relative ages expressed on thr geological timescale are primarily resulted from the study of…?
fossil content and spatial relationships among sedimenatry rocks
Dendrochronology involves dating of historic and geologic events through the study of …?
annual growth rings in trees
what does the principle of uniformitarianism imply?
physical processes observed today have been active in the past and are preseved in the rock record
which method of correlation is the most reliable for determining age equivalence among bodies of rock that are physically seperated by vast distances?
fossil correlation
radiometric dates applied to sedimentary rocks produce ages that…?
are too old - predate sedimentary deposition
the surface below sedimentary rocks that overlie igneous or metamorphic rocks is called…?
a nonconformity
buried erosional surfaces between sedimentary strata are called …?
disconformities
what does the ‘closure temperature’ represent?
the point when isotopes are no longer free to move out of a crystal lattice
