# 3CarbonDating.ppt 100KB Jun 23 2011 10:24:00 AM

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## Carbon Dating

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### Based on the rate of decay of the carbon

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 Cosmic rays enter the earth's Cosmic rays enter the earth's

atmosphere. They then collide atmosphere. They then collide

with an atom in the with an atom in the

atmosphere, creating a atmosphere, creating a

secondary cosmic ray in the secondary cosmic ray in the

form of an energetic neutron. form of an energetic neutron.

These energetic neutrons These energetic neutrons

collide with nitrogen atoms. collide with nitrogen atoms.

When the neutrons collides a When the neutrons collides a

nitrogen-14 (seven protons, nitrogen-14 (seven protons, seven neutrons) atom turns seven neutrons) atom turns

into a carbon 14 atom (six into a carbon 14 atom (six

protons, eight neutrons) and a protons, eight neutrons) and a

hydrogen atom (one proton, hydrogen atom (one proton,

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### How Carbon Dating Works

 The carbon content of living matter is constantly The carbon content of living matter is constantly

renewed so the proportion of carbon 12 to carbon 14 is renewed so the proportion of carbon 12 to carbon 14 is

the same the same

 The rate Carbon 14 forms seems to be constant. The rate Carbon 14 forms seems to be constant.

Therefore by measuring the ratio between carbon 12 and Therefore by measuring the ratio between carbon 12 and

the carbon 14 in a dead organism and comparing it to the carbon 14 in a dead organism and comparing it to

the ratio in living things, a measurement of time is made. the ratio in living things, a measurement of time is made. Because the rate of decay for carbon 14 is 57,000 years, Because the rate of decay for carbon 14 is 57,000 years,

carbon dating is only reliable for dating things up to 60, carbon dating is only reliable for dating things up to 60,

000 years old.

000 years old. As soon as a living organism dies, it stops As soon as a living organism dies, it stops taking in new carbon.

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### Half Life of Carbon Dating

 Half-Life refers to the time taken Half-Life refers to the time taken

to lose half of radioactivity: the

to lose half of radioactivity: the

takes to lose half its

takes to lose half its

 The Half-Life of Carbon 14 is The Half-Life of Carbon 14 is

5730 years. For example, if a

5730 years. For example, if a

relatively large sample of

relatively large sample of

Carbon 14 was left untouched

Carbon 14 was left untouched

for 5730 years, half of it would

for 5730 years, half of it would

remain and the other half would

remain and the other half would

decay.

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