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LEC 103 environmental processes and systems > lecture 2 > Flashcards

lecture 2 Flashcards

1
Q

what two ways can age of rocks be derived?

A

relative dating

absolute dating

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2
Q

what does relative dating involve

A

the principles of stratigraphy and palaeontololgy

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3
Q

what is stratigraphy

A

study of rock layers

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4
Q

what is palaentology

A

study of fossils

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5
Q

how do you carry out relative dating

A

looking at layers of rock (lower down = older) to determine the ages of rocks, sediments and landforms. you can tell how old it is relative to the other rocks around it

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6
Q

what is a geologic calander/timescale?

A

a chronology of events on Earth based on

obtaining ages of past events.

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7
Q

what does absolute dating involve?

A

knowledge of radioactive decay

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8
Q

why do we use radioactive decay as a clock?

A

the decay rate/half life of radioactive atoms is known for
radioactive isotopes e.g. 87Rb, 238U, 40K, 235U, 14C
• the decay rate/half life does not vary with changes in Temp or Pressure which typically accompany geologic processes
• we can measure the ratio of parent to daughter atoms in a rock sample

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9
Q

what are the isotopes that are commonly used for absolute dating?

A 
rubidium 87
uranium 238
potassium 40
uranium 235
carbon 14
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10
Q

daughter isotope of rubidium 87 and half life and materials that can be dated

A

strontium 87
49 billion years
muscovite, biotite

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11
Q

daughter isotope of uranium 238 and half life and materials that can be dated

A

lead 206
4.5 billion
zircon, apatite

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12
Q

daughter isotope of potassium 40 and half life and materials that can be dated

A

argon40
1.3 billion
muscovite, biotite, hornblende

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13
Q

daughter isotope of uranium 235 and half life and materials that can be dated

A

lead 207
0.7 billion
molluscs and corals

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14
Q

daughter isotope of carbon 14 and half life and materials that can be dated

A

nitrogen 14
5730
wood, charcoal, peat, bone, tissue, shells

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15
Q

what is half life

A

the time for one half of the original

number of radioactive atoms to decay

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16
Q

how do you use this information to work out how old things are?

A

you measure the number of parent and daughter atoms using a mass spectromiter. then, becuase you know the half life of the parent, the number of daughter isotopes is just the number of half lives that have passed, multiplied by the OG number of parent isotopes so you can work out how many half lives have gone and thus, the age of the specimin.

17
Q

what happens in decay

A

a neutron spits out an electron and becomes a proton

LEC 103 environmental processes and systems (1 decks)

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