Chemistry Reference
In-Depth Information
Soils altered in the past by human habitation are not difficult to find. Farmers
in many regions of North America, for example, noted that the soil of old
Indian villages was more productive than adjacent soils. The unique prop-
erties of soils from ancient inhabited places have frequently been put to use
in many places in the world; farmers in the Ashdod area in Israel and El
Phosfat in Egypt, for example, used the soil that they excavated from ancient
archaeological sites to fertilize the land they cultivated (Wright 1986).
Alteration of Soil by Human Habitation.
Humans inhabiting a site leave
buried or partly buried remains of their existence (excreta and dead human
remains) and of their activities [ashes, domestic plants, and animal remains
(blood, flesh, and bones), food wastes, and byproducts of manufacturing
undertakings]. After burial, these remains are affected by weathering and
diagenetic processes (see Textboxes 45 and 46) and eventually become part
of the soil, altering its composition. Thus, the chemical composition of soils
at sites of past human habitation preserves information on changes brought
about by human activity. Using modern chemical and physical techniques it
is possible to study much of this information (Retallack 2000, 1990; Groen-
man van Waateringe and Robinson 1988).
The chemical elements that may provide clues for recognizing and locat-
ing sites of past human habitation are mainly
carbon
,
nitrogen
, and
phospho-
rus
.
Carbon
is derived from all forms biological matter;
nitrogen
, mostly from
amino acids in plant and animal proteins; and
phosphorus
, from the bones
and excretions of humans and animals. The amounts of carbon and nitrogen
added to the soil are relatively large (since most discarded wastes are com-
posed of organic matter); these elements are, however, also subject to deple-
tion during decay processes, and much of them is lost: carbon, mainly
through biooxidation processes and nitrogen, in a number of ways. Not so
phosphorus, which, when deposited in soil, becomes
fixed
and is not subse-
quently depleted. It has been calculated that a community of 100 people
living in an area of one hectare (10,000 m
2
) may provide an annual increment
to the soil of about 120 kg of phosphorus. Relative to the amounts of this
element naturally present in the soil, this is a considerable addition, repre-
senting an annual increase of up to one percent of the phosphorus in the
uppermost horizon of soil. The relative amount of phosphorus in the soil
provides, therefore, an indicator of the extent, duration, and nature of past
human habitation. Measuring the relative amount of phosphorus in the soil
has, therefore, become a quite widely used tool for surveying archaeologi-
cal sites, but also to appraise the intensity and/or duration of past human
habitation at a site (Bethell and Máté 1989; Rottländer 1983).
