worksheet 2

Question 1

what is relative dating

Answer 1

determining dates of geological units in relative sense (this comes before this… and this comes after this…)

Question 2

what is absolute/numerical datng

Answer 2

provides actual date of how old rock/feature is

Question 3

what is magnetic dating

Answer 3

dating of rock using reversals of Earth’s magnetic field to help determine age of rocks

Question 4

what is radiometric dating

Answer 4

a strategy to determine the absolute age of rock using the ratios unstable isotopes in minerals and organic matter

Question 5

what isotopes are good for absolate dating?

Answer 5

U-Pb (Uranium Lead), Rb-Sr (Rubidium-Strontium), Th-K (Thorium-Potassium) and K-Ar (Potassium-Argon)

Question 6

can we use radiocarbon dating for old rocks?

Answer 6

no bc short half life so really only works for things ~<50,000 years old

Question 7

what isotopes have really long half lives?

Answer 7

U-Pb or K-Ar

Question 8

what is the equation for the number of remaining radioactive atoms when using radiocarbon dating?

Answer 8

N=N_0 e^(−λt)
N_0 is number of original radioactive atoms
λ is nuclide decay constant
λ= ln (2) / t^½
t^½ is the half life

Question 9

what is the age equation and when is it used?

Answer 9

used for all dating when you do not have carbon
t= 1/λ * ln ( 1+ D / P )
D –> daughter isotopes
P –> parent isotopes
λ= ln (2) / t^½

Question 10

what are possible assumptions made in radiometric dating?

Answer 10

• no other factors altered amount of parent & daughter isotopes
• no daughter isotopes existed at time zero
• decay constant is actually a constant and doesn’t vary throughout time
• parent and daughter isotopes can be accurately measured

Question 11

what is the principle of superposition

Answer 11

in an undeformed sequence, the oldest rock is at the bottom and the youngest is at the top

Question 12

what is the principle of originally horizontally

Answer 12

layers of sediment are deposited more or less horizontally

Question 13

what is the principle of cross cutting relationships?

Answer 13

if a feature crosses multiple layers then it was formed after the features that it crosses

Question 14

what is principle of faunal succession

Answer 14

fossil species succeed each other in a definitive recognizable order. one the species goes extinct, it will not appear as a fossil in a different time period

Question 15

what are unconformities

Answer 15

surface that represents break in rock record due to deposition stopping and allowing erosion to occur and then deposition occurs again

Question 16

what is an angular unconformity

Answer 16

when the underlying older rocks and the overlying younger rocks show angle to one another. the rocks below were tilted/folder and then there was weathering and then new rocks were deposited

Question 17

what is a disconformity

Answer 17

when the older rocks and the younger rocks are parallel but the contact plane (where they touch) is an erosional surface

Question 18

what is a nonconformity

Answer 18

when the underlying rocks are igneous or metamorphic (unstratified) and the overlying younger rocks are sedimentary (so they are stratified)

Question 19

what is biostratigraphy

Answer 19

using fauna and fossils to determine relative age of layer order and combine that with stratigraphic units

Question 20

how can biostratigraphy help us determine relative age

Answer 20

we can use the presence of absence of certain fossils and combine with the principle of faunal succession