14C
The ratio of
to
in atmospheric
carbon dioxide
remains fairly
constant over time
12C
Carbon reacts with
oxygen in air to
produce carbon
dioxide. Both I4CO2
Because 14C is12
and CO2 are The 14C in the CO2
constantly being
decays back into I4N
produced.
produced (by
by emitting a beta
bombardment) The collisionparticle.
of high This decay
and depleted (byenergy neutrons
withis very slow
process
14N
14C 14
decay), it reaches
a produces
since C has a long
steady-state
atoms. A proton
is (5730 years).
half-life
concentration in also
the ejected in the
This
equilibrium
atmosphere.
process. is
comparable to water
trickling into a cup
with a small hole in it.
The water will
eventually reach a
constant, stable level
in the cup
High energy neutrons
from space collide
with atoms in the
Earth's upper
atmosphere.
Carbon dioxide is
evenly distributed
throughout the entire
atmosphere, even at
ground level!
Carnivores eat
herbivores and
incorporate the 14C
stored in herbivores
into their tissues.
The 14C/12C ratio in
carbohydrates
produced during
photosynthesis is
equivalent to the
ratio of these two
isotopes in the
atmosphere.
A herbivore eats
The 14C/12C ratio in
plants. It
dead tissues
incorporates some
decreases over time
of the carbon
because 14C decays
Atoms from starch
but 12C does not.
and carbohydrates
into its tissue and
Plants consume
exhales
atmospheric
carbon
Organisms die
and
some carbon atoms
dioxide during
decay through
As long as an
in the form of carbon
photosynthesis
natural processes.
organism consumes
dioxide.
Any decrease in the
carbon containing
total amount of
materials it will
carbon due to
maintain a constant
decomposition will
14C/12C ratio.
not effect the 14C/12C
ratio.
An archeologist
discovers a spear or
a similar carbonbased artifact.
Using a Geiger
counter, the radioactivity of the artifact
can be measured.
From this the ration
of 14C/12C in the
artifact can be
calculated.
An ancient ancestor
cut down a tree and
carved it to make a
spear.
The radioactivity
can then be
compared with the
activity level in
comparable
living tissue
Modern methods of
C-14 dating utilize
mass spectrometry
which detects the
number of C-14 and
C-12 atoms.
By knowing how
much this ratio has
decreased, we can
determine how old
the artifact is. This
is known as C-14
dating.