Page 124 - Science Course 3 (Book 2)

Mo11-L3b: How to Determine Absolute Ages?

Radiocarbon dating is useful for measuring the age
of the remains of organisms that died up to about
50,000 years ago.

“Parent” uranium
changes into
UU “daughter” lead. UU
UU UU PbPb PbPb
UU UU

Unstable atoms, such as uranium(U), eventually Radiocarbon laboratory measures how much
change into stable atoms, such a lead(Pb). The C–14 is left in the bone awl to determine when
Original version is called a parent atom (or isotope), the turkey died.
and the new version is called a daughter atom.

The ratio of U-235 to Pb-207 in a mineral can be
measured to determine the age of the rock
containing the mineral.
Carbon plant absorbs carbon
(C) during photosynthesis.

Turkey consumes carbon Uranium–235 Dating
when it eats the corn. Carbon
Ratio of Parent to Daughter 1/2
is absorbed into all its tissues, 1
including its bones.

1/4

0
C–14 0.704 1.408 2.112 2.816
Turkey is butchered, and
C–14 one of its leg bones is Billions of Years
fashioned into a bowl
C–14 awl. Parent (unstable)

Daughter (stable)
As soon as the turkey dies,
the carbon it absorbed
during its lifetime begins An unstable parent isotope(U-235) will decay at a
to decay at a known rate, constant rate and form a daughter product (Pb-207).
releasing radioactive After one half-life, the concentrations of parent and
carbon–14(C–14) from all daughter isotopes are equal.
its tissues, including the
bone awl. The parent isotope will continue to decay over time.
After two half-lives, 1/4 of the original parent
remains. After three half-lives, 1/8 remains, and
so on.
Archaeologist f nds
turkey bone awl during
excavation.
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