Geoscience Reference
In-Depth Information
may be difficult (see
Chapter 11,
p. 234 and
Chapter 17,
p. 407). Former sea levels are recognized by relict shore-
lines above, or river channels (as buried channels) below,
modern counterparts. Previous snowlines and trimlines
are inferred from landform evidence explained later in this
chapter. As with stratigraphic evidence, relict geomorphic
features are rarely continuous over long distances and
repeated expansion and contraction of ice sheets, sea level
and lakes tend to obliterate evidence of earlier events.
However, this can assist with relative dating; a series of
valley moraines or a vertical sequence of raised beaches
are indicative of glacier retreat and progressively falling
sea levels respectively, since advancing glaciers or rising
sea level would obliterate them. Altitudinal correlation
between sites often encounters problems with landforms
formed horizontally or at low angle, such as river terraces
and wave-cut platforms, subsequently warped by change
of datum. These are increasingly resolved using com-
puterized
geomorphometric
techniques, linking high-
resolution
electronic distance measurement
(EDM) and
global positioning systems
(GPS), to create
digital elevation
models
(DEM).
at Creswell Crags, Nottinghamshire. The caves show signs of
Upper Palaeolithic human occupancy.
Photo: Ken Addison
hominids probably responding to progressive desiccation
and resultant habitat changes in Africa. The appearance
of our genus,
Homo
, coincided with climate deterioration
marking the start of the Quaternary. Thereafter, episodic
dispersals - no doubt facilitated by alternation of cold/
temperate stage habitats and fluctuating sea level - saw
Homo erectus
in Asia by 1.6 Ma
BP
and
Homo heidel-
bergensis
in Europe by 780 ka
BP
. The widely accepted
'Out of Africa' dispersal leading to anatomically modern
species
Homo sapiens
is less than 200 kyr old, colonizing
Australia and the Americas within the past 50 kyr. The
oldest known British human fossil is a male shin bone
(
H. heidelbergensis
) of
c.
500 ka
BP
age found in gravels at
Boxgrove, Sussex.
Early human fossils and evolution
A great fascination of the Quaternary period lies in the
coincidence of human evolution with repeated, rapid
large-scale global climate and land surface change. More-
over, the record comprises not just human subfossils
and response to environmental conditions. Our human
'footprint' is increasing exponentially, from large-
mammal extinctions in Late Palaeolithic times (
Plate 23.6
)
through early farming during the Mesolithic-Neolithic
transition and widespread temperate deforestation from
the Bronze Age, to whole-landsystem and climate change
of the industrial age (
Figure 23.4
).
Geoarchaeology
bridges
environmental and anthropological studies of what may
become known as the
Anthropocene
epoch of Earth history
(Crutzen and Stoermer, 2001), using Earth science
principles and techniques reviewed so far. Our knowledge
of the earliest stages of human evolution rests on frag-
mentary, pre-Quaternary series of incomplete body fossils
(mostly skulls) and trace fossils (mostly footprints).
African primates (apes) shared a common ancestry with
hominins (early humans) between about 8-6 Ma ago
during the Miocene epoch, in eastern and southern Africa.
Climate change strongly influenced evolution, initially
in the emergence of upright-walking
Australopithecine
Artefacts and prehistoric cultures
The earliest geoarchaeological records therefore share
a body, trace and subfossil record, history of evolution
and succession of the biosphere and principles of
biostratigraphy in general. What sets it apart is the
evidence of human use of
artefacts
(tools) to physically
transform the land surface, with built structures mimic-
king landforms. Most of human prehistory is represented
in this way, rather than as human remains, posing
particular questions for interpretation and reconstruction.
To archaeologists, an artefact represents an
action
or
capacity to achieve a particular task. Successively larger
collections of generically similar artefacts parallel the
bundles of sedimentary facies or communities of fossil
taxa reinforcing environmental reconstruction. Several
artefacts identify an
assemblage
, several assemblages an
