Geoscience Reference
In-Depth Information
THE ICE AGE TIMESCALE AND LANDSCAPE MODIFICATION
The most recent Ice Age began about 2 million years ago, and is still continuing in
Arctic areas. At various times during this period ice has thickly covered most of north-
west Europe. Recent research, particularly measurements of oxygen isotopes in po-
lar icecaps and oceanic sediment drill cores, has revealed much of the detail of how
the climate has changed during the current Ice Age. It has been discovered that long
cold periods have alternated with short warm periods in a complex but rather regular
rhythm. Looking at the last half-million years, this alternation has occurred about every
100,000 years, and this is now known to have been a response to regular changes in the
way the Earth has rotated and moved in its orbit around the sun. A closer look at the
last million years (Fig. 13) reveals that for more than 90 per cent of the time conditions
have been colder than those of today. Warm (
interglacial
) periods, like our present one,
have been unusual and short-lived, though they have often left distinctive deposits and
organisms.
FIG
13.
The last million years of global temperature change.
*the Oxygen Isotope Stages are an internationally agreed numbering sequence to label
the succession of climatic cold (even numbers) and warm (odd numbers) episodes.
One of the most important cold episodes (
glacials
), just under half a million years
ago, resulted in the Anglian ice sheet. This was up to several hundreds of metres thick
and extended from the north southwards, well into Southern England, covering much
of East Anglia and the north London area (Fig. 14). As the ice spread slowly south-
wards, it was constricted between the Chalk hills of Lincolnshire and those of Nor-
folk. A wide valley, later to become the Wash and the Fens, was filled with ice to a
depth well below that of present sea level. As the ice spread outwards from this valley
it dumped the rock material it was carrying, including blocks and boulders up to hun-
dreds of metres across, giving some idea of the tremendous power of the ice sheet. The
