Mother of pearl -- produced by molluscs -- is largely used in
jewellery and art. However, a new report suggests that it could be
used to reveal both the temperature and the ocean depth at which
the material formed.
Mother of pearl, or nacre, has been the subject of scientific
scrutiny because it has a unique structure that makes it 3,000
times more fracture-resistant than the mineral from which it is
made, aragonite. A new report by the University of
Wisconsin-Madison in the Journal of the American
Chemical Society shows that temperature and depth can be
deduced by looking at the structure of the nacre.
The thickness of the nacre layers correlate to the water depth
at which the material was assembled by a mollusc. Meanwhile the maximum temperature can be measured
by looking at how disordered the nacre crystal orientations are. If
the techniques used by the Wisconsin group can be applied to fossil
nacre, scientists could start to accurately reconstruct a global
record of ancient environments and environmental change.
Gilbert, a UW-Madison professor of physics and chemistry, says:
"If the correlation holds, we would have a thermometer that goes
back in time, a paleothermometer of how hot or cold water temperatures were when the nacre formed."
The team tested nacre from eight different mollusc species from
different environments. They compared the structural make-up of the
nacre to key ocean parameters including maximum, minimum and mean
annual temperatures as well as maximum and minimum water pressure.
The team found an extremely high correlation between the
microscopic structural characteristics of their nacre specimens and
the temperature and pressure data obtained from the environments
where they were collected.
The team admits that further testing is needed, but Gilbert
believes that this could be an important breakthrough in
understanding the history of the ocean. She says: "All other
(temperature) proxies are based on chemical analyses and the
relative concentration of different elements or isotopes. This
could be our first physical proxy, in which the microscopic
structure of the material tells us the maximum temperature and
maximum pressure at which the mollusc lived."