Carbon dating

1. Carbon Dating I
• While alive, every being has a constant ratio
of C(14) to C(12)
– Cause: absorption from the atmosphere
• cosmic rays transform N(14) to C(14)
– N(14) + N --> C(14) + P
• the ratio of C(14) to other forms of carbon remains
constant during the lifetime of the object studied.
N
n C

2. www.c14dating.com
Carbon Dating II
• When Dead, no more absorption of carbon takes place
– the C(14) begins its decay to N(14)
• C(14) --> N(14)+ e
• hence the ratios of C(12) to C(14) change
• this change can be measured by
the rate of nuclear activity
• C(14) has a half-life of
only 5730 years, so only
very young things can be
measured (~50000 yrs.)

3. Carbon Dating III
– Inaccuracies:
• the sun is not constant in its output
• many species do not attain carbon from the
atmosphere, etc.
– How to counteract the inaccuracies
• tree rings, ice core samples
• fine-tune the model

4. http://archserve.id.ucsb.edu/Anth3/C
ourseware
Potassium-Argon Dating
• Argon gas in volcanic samples is measured
– Molten rock releases all argon initially present
– Argon is then formed by the decay of potassium
• K(40) + e ---> Ar(40) + e

5. www.c14dating.com
Potassium-Argon Dating II
– Only very small amounts are found, which is
the reason the K is not measured directly
– The argon is measured by mass spectometry
• the ratio of potassium to argon gives a date
– Objects as old as 4.5 billion years have been
measured