Chemistry Reference
In-Depth Information
original structure. The variety of minerals in petrified plants and animals
often creates strikingly vivid colors. Although the original biological matter
of the dead remains is removed, the natural cast often creates a precise
mineral reproduction of plant or animal remains (Donovan 1991; Fortey
1991).
The course taken by any particular fossilization process is, therefore,
determined by the physical and chemical factors prevalent in the environ-
ment of the dead remains. The physical factors include temperature, degree
of aeration, and rate of flow of groundwater. The nature of minerals and
rocks, and of the groundwater at the site of burial, are the most important
chemical factors. Reconstructing and explaining the processes undergone by
dead remains, from the time of death to when they are fully fossilized, is the
concern of
taphonomy
, the study of the processes taking place when dead
remains pass from the biosphere to the lithosphere (see Textbox 69).
TEXTBOX
69
TAPHONOMY
Taphonomy
is the branch of science that studies the processes of
decay
and
fossilization
of the remains of dead organisms. The term
taphonomy
(from
the Greek
taphos
, burial and
nomos
, law) was introduced during the first
half of the twentieth century to describe the study of the transition of the
dead remains of organisms from the biosphere to the lithosphere. Archae-
ologically related taphonomic studies began much later, near the end of
the century (O'Connor 2005).
Taphonomic studies examine the processes taking place in the remains
of dead organisms during their gradual conversion from biological sub-
stances into the inorganic, lithic materials. After organisms die, their
remains undergo compositional degradation, passing through two succes-
sive and distinct taphonomic stages:
necrolysis
and
diagenesis
(Plotnick
1993; Shipman 1981).
Necrolysis
is the decomposition and dissolution of
the remains of living matter. Most dead remains vanish during this stage,
living no trace. Soon after death, parts or the whole of dead remains
decompose or vanish altogether as a result of the combined activity of
aerobic and anaerobic bacteria and the scavenging of the remaining soft
tissues by insects, reptiles, birds, and mammals. Often, only the bones
remain, which are attacked by other organisms. Under exceptional envi-
ronmental conditions, however, some dead remains withstand and outlast
the necrolysis stage in a somehow recognizable form. If and when they do
so, they enter the diagenetic stage, when they are gradually transformed
