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Flashcards in Geologic Time Deck (17):
0

how is relative dating different from absolute dating?

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

1

State the law of superposition

sediments are deposited in horizontal layers.
in undisturbed sedimentary strata the oldest rock is on the bottom

2

What is the principle of uniformitarianism?

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

3

What does the law of crosscutting say?

intrusions and faults are younger than the rock they intrude into

4

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

the pebbles found in the conglomerate

5

Define unconformity

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

6

What is a fossil?

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

7

List the 6 ways that fossils form

original remains
replaced remains
molds
casts
trace
carbonaceous films

8

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

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)

9

How is a radioactive isotope used to determine absolute age?

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

10

What is a half-life?

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

11

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

nitrogen-14
5730

12

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

lead 206
4.5 billion years

13

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

strantium 87
47 billion

14

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

argon 40
1.3 billion

15

What isotope is used to find the age of organic remains

carbon 14

16

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

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