Travel Reference
In-Depth Information
Figure 105
Australian pelicans,
Pelecanus conspicillatus
, cruise quietly along the green
banks of the Bensbach.
In many cases the burned bones are too old to be dated directly using the
carbon-14 method, but it is possible to date the sand grains that currently
surround them. Or, to be precise, it is possible to date the time at which the
sand itself was last exposed to sunlight.
The dating techniques depend on the fact that sand grains contain crys-
talline materials that gradually accumulate energy, through natural radioac-
tivity and cosmic rays. Electric charges gather at faults in the grains' crystal
structure at a steady rate over time. But this clock of accumulating energy is
set to zero whenever the sand grains are exposed to sunlight, which blasts
away the accumulated charges.
