geological time

Question 1

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?

Answer 1

1 billion years

Question 2

An igneous dike cuts across a sequence of sedimentary beds, which is older?

Answer 2

the sedimentary beds

Question 3

what happens after an unstable parent isotope decays?

Answer 3

the daughter isotope may continue to decay

Question 4

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…?

Answer 4

baked contracts

Question 5

Magnetostratigraphy takes advantage of the fact that Earth’s magnetic field…?

Answer 5

has experienced numerous polarity reversals, with periods of normal and reversed polarity of varying lengths

Question 6

can the age of earth be reliably estimated from sediment thickness?

Answer 6

no - much of earths history is represnted by unconformities between strata rather than the strata themselves

Question 7

what principle did James Hutton put forth?

Answer 7

principle of uniformitarianism

Question 8

if the relative ages of 2 formations are known, what else about them can be inferred?

Answer 8

their relative position in a sequence of rock layers

Question 9

seasonal changes create layering in glaciers known as…?

Answer 9

rhythmic layering

Question 10

in an undisturbed sequence of sedimentary rocks, younger layers overlie older layers, according to the principle of..?

Answer 10

superposition

Question 11

if horizontal sedimentary strata overlietilted strata (and no fault is present), the surface between the horizontal and tilted strata must be an…?

Answer 11

angular unconformity

Question 12

how much of a radioactive parent isotope will remain after 3 half lives have passed?

Answer 12

one eighth

Question 13

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?

Answer 13

200 million years

Question 14

which eon of geological time is represented by rocks containing an abundant shelly fossils?

Answer 14

phanerzoic

Question 15

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 …

Answer 15

original horizontality

Question 16

why is radiocarbon dating only rarely applied in geological work?

Answer 16

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

Question 17

relative ages expressed on thr geological timescale are primarily resulted from the study of…?

Answer 17

fossil content and spatial relationships among sedimenatry rocks

Question 18

Dendrochronology involves dating of historic and geologic events through the study of …?

Answer 18

annual growth rings in trees

Question 19

what does the principle of uniformitarianism imply?

Answer 19

physical processes observed today have been active in the past and are preseved in the rock record

Question 20

which method of correlation is the most reliable for determining age equivalence among bodies of rock that are physically seperated by vast distances?

Answer 20

fossil correlation

Question 21

radiometric dates applied to sedimentary rocks produce ages that…?

Answer 21

are too old - predate sedimentary deposition

Question 22

the surface below sedimentary rocks that overlie igneous or metamorphic rocks is called…?

Answer 22

a nonconformity

Question 23

buried erosional surfaces between sedimentary strata are called …?

Answer 23

disconformities

Question 24

what does the ‘closure temperature’ represent?

Answer 24

the point when isotopes are no longer free to move out of a crystal lattice

Question 25

Numerical ages for boundaries between time units on the geologic time scale primarily resulted from the study of ________, in conjunction with relative age data.

Answer 25

radiometric dating of igneous rocks

Question 26

a radiometric age for a mineral crystal within an igneous rock measures the ammount of time that has passed since the ..?

Answer 26

temperature of the crystal became equal to the closure temperature of the mineral

Question 27

how is the half life of a radioactive parent isotope defined?

Answer 27

the time ot takes for half of the parent isotope to decay to daughter isotopes