ARCHAEOLOGICAL CHEMISTRY—EXPLORING HISTORY WITH CHEMISTRY - Chemistry: Notable Research and Discoveries - page 173

The mummy only weighs about 30 pounds (13 kg) and is about five
feet (1.54 m) in length, but because of shrinkage this does not reflect
the Iceman's true physique. According to the South Tyrol Museum of
Archaeology in Bolzano, Italy, which houses the body, the living Ötzi
would have been about 63 inches tall (1.6 m) and weighed 110 pounds
(50 kg).
But where did he come from? He may have been raised in the same
region where his body was found, or he might have been a newcomer
to the area, or just traveling through. To determine which is the case,
chemists and biologists have developed techniques that make use of
certain isotopes. As with forensic evidence, these isotopes can be found
in Ötzi's teeth and bones.
A tooth consists of dentin, which gives the tooth its shape and size,
and a covering of enamel, which is extremely hard—enamel is the hard-
est material in the body—and protects the tooth from the grinding and
chewing associated with eating. (Even so, some of it wears away over
the years, providing an indication of age.) Both dentin and enamel are
primarily made of calcium phosphate, but there are differences in how
the body generates these two structures. Enamel forms only once, when
the tooth initially grows, and has to last a lifetime. Dentin, however,
gets slowly replaced throughout life. Bone is similar to dentin and also
experiences gradual turnover.
Because tooth enamel forms only once, its structure supplies a
“snapshot” of the time of tooth formation, which occurs early in life.
The tissues and structures of the body are built from elements supplied
by food and water. For enamel, these elements consist of those that were
available during childhood. The key to identifying where the Iceman
spent his childhood comes from the variation in isotopes that occur in
different regions.
Calcium is an important element in teeth and bone, but strontium
is chemically similar and can replace calcium in these structures. This
is important to archaeologists because certain strontium isotope ratios
vary in soils—and therefore vary in the foodstuffs grown in those soils.
For example, the ratio of stable isotopes strontium 87 to strontium 86
can be a distinct marker for certain soils. Another important element is
oxygen, which is a major component of calcium phosphate. Oxygen can
be incorporated into the body from food or water, and ratios of oxygen
18 to oxygen 16 often distinguish geographic location.