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A2 earth life and climate > absolute dating > Flashcards

absolute dating Flashcards

1
Q

problems with radiometric dating in sed. rocks

A

weathering and erosion - breaks down closed system, minerals gain or lose atoms

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2
Q

what are symbols for potassium - argon dating

A

K-Ar

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3
Q

what are the values for K-Ar dating

A

40K-40Ar

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4
Q

which is the most widely used form of dating

A

K-Ar

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5
Q

where can you fins Potassium (k)

A

muscovite
biotite
hornblende
glauconite

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6
Q

what is half life of K

A

1260 Ma

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7
Q

K can be used to date rocks at..

A

the time of their crystalisation

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8
Q

how is K-Ar dating unique

A

11% of potassium decays to for Argon gas WHICH IS NOT FORMED ANY OTHER WAY

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9
Q

in which speed of cooling rocks is K-Ar dating most usedful

A

rapidly cooled rocks

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10
Q

problem with dating K-Ar rocks?

A

Ar is a gas so it can escape

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11
Q

which rocks (ign, sed, met,) is Ar found in?

A

IGNEOUS SEDIMENTARY AND METAMORPHIC

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12
Q

What are symbols for Rubidium - Strontium dating

A

Rb-Sr

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13
Q

what are values for Rb-Sr

A

87Rb-87Sr

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14
Q

Rb-Sr is found in which minerals

A

muscovite
biotite
K-feldspar

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15
Q

what is Rb Rubidium half life

A

50,000 Ma

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16
Q

benefits of Rb-Sr dating

A

Rb decays to Sr which is a SOLID so less likely to escape than Argon

17
Q

best rocks to date using Rb - Sr

A

metamorphic rocks

18
Q

which rocks can be dated with Rb-Sr

A

metamorphic

igneous

19
Q

how can K-Ar dating be inaccurate in sedimentary rocks?

A

Daughter Ar is a gas so escapes so there are LESS daughter atoms and the rock is interpreted as OLDER

20
Q

how can CLASTS in sedimentary rocks be an issue when it comes to K - Ar dating

A

can give results for a whole range of ages as the clasts are younger than the rest of the rock

21
Q

problems with dating metamorphic rocks

A

parent and daughter atoms can be gained and lost during heating events
metamorphosis can RESET THE RADIOMETRIC CLOCK in some minerals and not others

22
Q

problems in dating igneous rocks

A

large scale intrusions can take 10,000s years to cool, different parts reach closing temp before others

23
Q

where are the most reliable igneous rock dates found

A

small fast cooling intrusions/extrusions

24
Q

symbols for Uranium - lead dating

A

Ur-Pb

25
Q

values for uranium-lead dating

A

238Ur - 206Pb

235Ur - 207Pb

26
Q

Ur-Pb what rocks is this found in

A

zircon

uranite

27
Q

which rocks can Ur Pb dating be used in

A

igneous

28
Q

halflife of Ur-Pb

A

4,500 Ma

29
Q

what is a half life

A

time taken for half the parent (unstable) atoms to decay

A2 earth life and climate (15 decks)

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