24 BASICPRINCIPLES – MAKING THEMOST OF THECLUES
- why information is missing (dug away);
- why information appears (appears at bottom of a
hole dug into surrounding layers); - why information cannot be used directly (dug
away and re-deposited later); - unusual information (odd shaped hole, unusual
orientation, not refilled quickly); - unusual information arrived at same time (two bodies,
mother/child, male/female – i.e. cut–bodies–fill); - dating information (shape, orientation and depth of
hole); - social information (shape, orientation and depth
of hole, location of body and artefacts in hole); - artefact information (stains, fragments);
- structural information (stains, fragments, subsidence).
The human and natural processes that have the poten-
tial to disturb, remove or cover archaeological remains
do not only occur at sites such as graveyards. Cultural
and natural processes are constantly occurring across the
landscape, foreshore and sea-bed. Through maintaining
detailed archaeological records of ‘contexts’, it is possible
to recognize processes that have affected the remains.
This type of information is important for the full inter-
pretation of archaeological sites. The detailed examination
of contexts is just as relevant under water as it is on land.
For example, throughout the life of a vessel, activities add
and remove material (e.g. loading and unloading of crew,
cargo and equipment, repairs, changes in design). Even
before a vessel sinks, it is a patchwork of different events
or occurrences giving evidence of relevant circumstances
or contexts. On sinking, all this evidence is taken to the
sea-bed where a whole new series of processes affect the
ship and turn it into the archaeological site encountered
today. Scouring, silting up, collapse, salvage, disturbance
by trawling, burrowing organisms, looting, etc. are all
processes that can affect the archaeological evidence.
DATING
Since archaeologists are studying the past and the passage
of time, one of the main things they want to extract
from clues is the point in time to which they relate.
Chronologies or timescales provide the ability to relate
events or features throughout antiquity and across the
world. Widely separated cultures such as the South
American civilizations and those in the Old World can
be compared if dates exist for each. In the same way,
through the use of techniques such as tree-ring dating
(dendrochronology) and radiocarbon dating, sites such
as submerged prehistoric settlements can be compared
across the world. Dating techniques can be grouped into
two main categories, absolute and relative dating, which
reflect the ways in which the particular methods can
be related to the present day.Absolute dating
Methods of absolute dating can be related to calendar
years and therefore the results of these techniques can
be directly related to the present day. To say that an event
happened 900 years ago is to give it an absolute date.
Absolute dating techniques often require specialist scientific
analysis. The range of dating techniques available for
different evidence types is growing as new methods and
approaches are developed. This section introduces three
commonly used methods of absolute dating to demon-
strate their potential and to show some of the associated
problems.Dendrochronology (tree-ring dating): Many wet sites
will produce large quantities of wood, which fortunately
can sometimes help in providing dating evidence. As
trees grow they produce annual rings whose width varies
according to the local conditions (figure 4.5). This pat-
tern is similar amongst trees of the same type in the same
area. This means that the same years can be recognized
in individual trees. Overlapping the tree-rings from trees
of slightly different dates can extend the sequence of
years. This has been done for oak until the sequence
extends from the present to, in some areas, 9000 years ago.
Tree-ring dating is based on matching the pattern of
growth rings found on a wood sample from a site with
its place in the established local sequence of variation
in growth ring size (figure 4.6).Figure 4.5 Tree-rings viewed through a microscope.
(Photo: Mark Beattie-Edwards)