earth time

Question 1

principle of uniformitarianism

Answer 1

processes seen today are the same as those of the past

Question 2

relative ages

Answer 2

based upon order of formation
qualitative method
older vs younger relationships

Question 3

numerical ages

Answer 3

actual number of years since event
quantitative method

Question 4

original horizontality

Answer 4

sediments settle out of a fluid by gravity
sediments accumulate horizontally, not favoured on slope

Question 5

principle of superpositio

Answer 5

younger strata on top, older on bottom

Question 6

principle of lateral continuity

Answer 6

strata form laterally extensive horizontal sheets
erosion dissects one-continuous layers
flat rocks unlikely to have been disturbed

Question 7

principle of cross-cutting relations

Answer 7

faults, dikes, erosion must be younger than the material that is faulted, intruded, or eroded

Question 8

principle of baked contacts

Answer 8

iegnous intrusion cooks invaded country rock
baked rock must have been there first (older)

Question 9

principle of inclusions

Answer 9

rock fragment within another
inclusions older than enclosing material
fragments older than igneous intrusion

Question 10

principle of fossil succession

Answer 10

fossils preserved in sedimentary rocks
they are time markers for relative age-dating
specific fossils found within limited time span
correlate strata locally regionally and globally

Question 11

unconformities

Answer 11

time gap in rock record

Question 12

angular unconformity

Answer 12

huge gap in time
horizontally parallel strata of sedimentary rock are deposited on tilted and eroded layers, producing an angular discordance with the overlying horizontal layers

Question 13

nonconformity

Answer 13

igenous/metamorphic rocks capped by sedimentary rock
I or M rocks exposed by erosion then sediment deposited on eroded surface

Question 14

disconformity

Answer 14

parallel strata bounding non deposition
interruption/pause in sedimentation

Question 15

correlating formations

Answer 15

formations can be traced over long distances
lithologic (rock type) and fossil correlation

Question 16

geologic maps

Answer 16

William Strata Smith noted that strata could be matched across distances. similar rock types in similar order

Question 17

geologic column

Answer 17

A geologic column is a record of the rock layers in a particular area across geologic time

Question 18

stratigraphic correlation

Answer 18

formations can be traced over long distances
overlap is sequences of rock types
overlapping rock columns used to build composite

Question 19

what is numerical age based on?

Answer 19

radioactive decay of atoms in minerals
decay proceeds at known fixed rate
radioactive elements act as internal clocks

Question 20

isotopes

Answer 20

elements that have varying number of neutrons.
stable: isotopes don’t change
radioactice: isotopes that spontaneously decay

Question 21

radioactive decay

Answer 21

progresses along decay chain. decay creates new unstable elements that also decay until reaching stable element endpoint

Question 22

parent and daughter isotope

Answer 22

parent: isotope that undergoes decay
daughter: product of this decay

Question 23

half life

Answer 23

time for half of unstable nuclei to decay
characteristic of each isotope
as parent disappears, daughter “grows in”

Question 24

isotopic dating

Answer 24

age of mineral determined by measuring ratio of parent to daughter isotopes. calculating time with known half life

Question 25

uranium lead dating

Answer 25

most trusted decay system for dating
determines the age of rocks and minerals by measuring the ratio of uranium to lead isotopes in a sample

Question 26

what does an isotope date mean?

Answer 26

gives time a mineral cooled below its closure temperature (when magma or lava cooled to become rock)
sedimentary rocks cannot be directly dated, but their minerals can

Question 27

other numerical ages

Answer 27

growth rings
rhythmic layering

Question 28

how old is oldest sandstone?

Answer 28

zircon
4.4 Ga