Geologic Time

Question 0

State the law of superposition

Answer 0

sediments are deposited in horizontal layers.

in undisturbed sedimentary strata the oldest rock is on the bottom

Question 1

how is relative dating different from absolute dating?

Answer 1

relative dating places events in sequential order of their occurrence.
absolute dating gives an actual date

Question 2

What is the principle of uniformitarianism?

Answer 2

geologic processes today are the same as they were in the past

Question 3

What does the law of crosscutting say?

Answer 3

intrusions and faults are younger than the rock they intrude into

Question 4

Which is older, a conglomerate or the pebbles that are ound in the conglomerate?

Answer 4

the pebbles found in the conglomerate

Question 5

Define unconformity

Answer 5

a buried erosional surface between rock layers that would not normally touch indicating- a missing section of rock history

Question 6

What is a fossil?

Answer 6

any evidence of past life preserved in rock (Ice or amber)

Question 7

List the 6 ways that fossils form

Answer 7

original remains
replaced remains
molds
casts
trace
carbonaceous films

Question 8

What is an index fossil used for? What are the 4 criteria for an index fossil?

Answer 8

indx fossils are used to help in the relative dating or rock layers. 4 criteria are easy to recognize, abundant, and short lived ,, and widespread (specific time/rock)

Question 9

How is a radioactive isotope used to determine absolute age?

Answer 9

by using the percentage (or ratio) of parent and daughter material to calculate half lifes and then age

Question 10

What is a half-life?

Answer 10

the time required for a radioactive isotope to decay by 50%, resulting in half the parent material atoms

Question 11

What is the decay product and the half life for the isotope Carbon-14

Answer 11

nitrogen-14

5730

Question 12

What is the decay product and half life for the isotope uranium 238

Answer 12

lead 206

4.5 billion years

Question 13

What is the decay product and half life for the isotope rubidium 87

Answer 13

strantium 87

47 billion

Question 14

what is the decay product and half life for the isotope potassium 40

Answer 14

argon 40

1.3 billion

Question 15

What isotope is used to find the age of organic remains

Answer 15

carbon 14

Question 16

If the half-life of an isotope is 10 years, how much will remain after 20 yeas?

Answer 16

25%
1 HL- 50%
2 HL- 25%