Re: Isotope Analysis

Phillip Bigelow (
Mon, 01 Jul 1996 19:08:15 -0700

Thomas Clarke wrote:
> Does anyone perform isotope analysis of hominid fossils?
> I recently read an article in _Nature_ discussing how
> O16/O18 ratios in whales teeth were being using to help
> resolve the issue of the point in whale evolution when the
> animals became independent of freshwater. It seems that
> freshwater and seawater have different O18 contents
> (I think due to differential evaporation rates,

Actually, it is due to the difference in thermal stabilities
between the two oxygen isotopes. Because of this
weight difference, on isotope is preferentially incorporated
into body tissues (and rocks as well) at lower temps. moreso
than the other isotope.

> ratios in ice cores have climatic implications).
> so that the teeth which are in isotopic equilibrium with body
> fluids can indicate when fresh water ingestion stopped in
> the fossil record.
> It seems to me that similar analysis might me useful in
> determining hominid diet shiftss. Other markers might
> be useful - fluorine?

Yes, trace element studies have been done on hominid teeth and bones.
To determine a sea-food diet, I can think of the following
elements that may have a relationship to the question:

Strontium, cesium, magnesium, manganese, and copper.
Certain rare-earths may also have a bearing on this question.

Fluorine is NOT used in trace element analysis, because it is a common
element in diagenetic alteration. I can't think of any others.
Iodine is also NOT used (even though it is a common marine element),
because it gets flushed out of the body after the thyroid gland
has absorbed enough of the element.
There may be more elements that are relatively more concentrated in
marine foods than in terrestrial foods.

Most recent isotopic studies on bone have concentrated on the ratios of
certain carbon isotopes, in order to determine the relative
importance of various land plants in the diet of animals.
This subject is well-studied, and there is a vast amount of
recent literature on it.