Geology Reference
In-Depth Information
older, the majority tried to reconcile what they observed with a
hundred million years. It triggered an explosion of attempts to
date the age of the Earth which, by the 1890s, had become a geo-
logical obsession. The Dating Game had started in earnest.
As Hutton and Lyell had shown, geological processes continue
all over the world in an endless cycle of erosion and sedimen-
tation, erosion and sedimentation. The process could be likened
to a gigantic hour glass in which erosion and sedimentation
continue unceasingly. Every time it rains water sinks into the
soil and promotes the slow work of decay by loosening parti-
cles. Every frost shatters the rocks with its expanding wedges of
freezing water. Large tree roots help by splitting the rocks
beneath the soil; smaller rootlets penetrate the crevices near the
surface creating material that is easily washed away by the rain.
Wind lifts up the lighter particles and carries them far and wide.
From high crags and cliffs sharp-cornered fragments of all sizes
fall down under gravity to the slopes below. The rain gathers in
runnels and washes the mud, sand and even gravel into rivers
which transport these particles to lower levels, ultimately
depositing them at the bottom of the sea where they accumu-
late, over very long periods of time, into very great thicknesses
of sediment. Eventually the hour glass gets turned upside down,
the bottom of the sea is uplifted into mountains, and the whole
process starts all over again. It therefore seemed evident to geol-
ogists who played the Dating Game, that if the rates of these
geological processes could be measured, then they could be
used to estimate an age of the Earth. Two of these 'hour-glass'
methods prevailed.
As well as carrying their visible load of mud and sand, rivers
hold in solution an invisible load: dissolved salts such as those
of calcium and sodium derived from decomposition of the rocks
over which the rivers pass. As far back as 1715 Edmond Halley,
