AGE DETERMINATION

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Age determination
Relative and absolute dating
Pa I 2 min
Students are provided with a jumbled list of events in a persons life (birth, primary,
secondary school etc) and must put them in chronological sequence
Varves
Pa I 10 min
Students correlate sections through varves to work out date of oldest bed.
Formation of varves
D
Showing students a photo or cross section of a tree showing tree rings can help them to
understand and remember the process of varve formation.
Radio activity
D
Geiger counter and radioactive sample to show that atoms are decaying all the time and that
they can be counted.
Half lives
A P F 30 min
This activity is to show how the numbers of atoms change as a radioactive element decays.
Students start with 100 dice and remove all sixes after each throw. They then plot a graph of
number of dice remaining against number of throws and from that work out the half life.
Parent and daughter
A P 15 min
Students work in pairs, one being the father and the other the daughter. The father has
£128,000 in his bank account and has agreed, having had his arm twisted by his beautiful
daughter, to give her half of his remaining wealth each year. The father writes down how his
wealth dwindles while the daughter writes down how much she receives, and what her total
wealth is each year. Marcia Bjornerud
Ratio of parent and daughter elements
Pa I 15 min
Students imagine they have 32 parent atoms and then work out the ratio of parent to
daughter elements for each half life e.g. one h.l. = 1:1, 2 h.l. =1:3, 3 h.l. = 1:7 and then the
percentage of daughter elements, 50%, 75%, 87.5% etc.
Ratio of parent to daughter elements
D
Start with 16 Smarties on the OHP. Remove half and replace with 8 Tictacs
Repeat by moving half the remaining Smarties and replacing them with an equal number of
Tictacs. Repeat until only one smarty is left. Students write down ratio and calculate
percentage. One can also show the effect on the ratio if some atoms such as argon are lost or
if it is all reset by metamorphism. This can also be done with each pair of students having
their own set of Smarties and Tictacs.
Idea taken from Chris
Bedford
Hour glass
D
We can not tell which atom will decay but we know when a certain percentage of atoms has
decayed. Likewise with the hour glass we do not know when a given sand grain will fall through
but we do know how long it will take for them all to fall through.

Earth Science Activities and Demonstrations