Week 1 Quiz - geological time Flashcards
Seasonal changes create layering in glaciers known as
rhythmic layering
Numerical ages for boundaries between time units on the geologic time scale primarily resulted from the study of ________, in conjunction with relative age data.
radiometric dating of igneous rocks
Uniformitarianism is succinctly summarized by:
The present is the key to the past
A radiometric age for a mineral crystal within an igneous rock measures the amount of time that has passed since the ________.
temperature of the crystal became equal to the closure temperature for the mineral
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 contacts
Radiometric dates applied to sedimentary rocks produce ages that ________.
are too old (predate sedimentary deposition)
Basaltic clasts within a conglomerate have been radiometrically dated to 50 million years ago. Is this a reliable age for the conglomerate?
No, this age is likely too old.
If horizontal sedimentary strata overlie tilted strata (and no fault is present), the surface between the horizontal and tilted strata must be a(n) ________.
angular unconformity
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
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.
The surface below sedimentary rocks that overlie igneous or metamorphic rocks is termed a(n) ________.
nonconformity
If 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 continuity
How much of a radioactive parent isotope will remain after three half-lives have passed?
one-eighth
If a basalt body cuts across a fault, what are the relative ages of the basalt and the fault?
The fault must be older, according to the principle of cross-cutting relationships.
When an unstable parent isotope decays
The daughter isotope may continue to decay
The closure temperature represents the point when ________.
isotopes are no longer free to move out of a crystal lattice
Buried erosional surfaces between parallel sedimentary strata are termed ________.
disconformities
Basaltic clasts within the basal layers of a conglomerate imply
The basalt must be the older of the two.
As understood by modern geologists, the principle of uniformitarianism implies that ________.
physical processes observed today (such as erosion and volcanic eruption) have been active in the past and are preserved in the rock record
What geological principle is a direct result of gravity
original horizontality
How is the half-life of a radioactive parent isotope defined?
The time it takes for half of the parent isotope to decay to daughter isotope
What geological principle is not a result of gravity
Cross-cutting relationships
In an undisturbed sequence of sedimentary rocks, younger layers overlie older layers, according to the principle of ________.
superposition
