Geography Reference
In-Depth Information
of Alpine glaciers were similar to those in the landscapes of the
Alpine foothills, the North German Plain, and the British Isles, far
away from any present-day glaciers. The evidence included signs
of the power of glacial erosion, (ranging from bedrock surfaces
polished by abrasion to deeply excavated 'U'-shaped valleys),
erratic boulders transported by glaciers for long distances from
their source areas, and moraines (ridges or mounds of unsorted
sediment deposited by glaciers). This evidence also illustrates the
fact that many landscapes cannot be explained by the processes
currently acting upon them.
Major conclusions of the early 'glacialists' were that extensive
glaciers and ice sheets once covered a much larger proportion
of the Earth than today, and that the Earth's environments
had recently been affected by an 'Ice Age'. Subsequently, it
was revealed that there had been more than one 'glacial'
episode, when global mean annual temperature was at least
10 degrees Centigrade lower than today; that these 'glacials' were
separated by 'interglacials' during which climatic conditions
were much like those of today; that global sea level varied by
over 100 metres due to the abstraction and release of water into
the oceans as the ice sheets waxed and waned; and that all the
components of the geo-ecosphere were profoundly affected,
including the tropical, arid, and warm temperate regions not
directly affected by glacier ice. These deductions provided an
alternative explanation of features previously attributed to
Noah's fl ood. They also represent the fi rst steps in our modern
understanding of Quaternary environmental change, in which
physical geographers play an important role. The Quaternary is
the geological term for the most recent major period of Earth's
history: it includes the present day and has lasted for more than
two million years.
Of the many advances in understanding Quaternary
environmental change, two can be regarded as particularly
