Geoscience Reference
In-Depth Information
represented in the geologial succession was most important. In a
recent volume published by the Geological Society of London to cele-
brate the bicentenary of the birth of Charles Lyell, Joe Burchfield
discussed the conceptual development of geological time. It required,
he noted, five essential ingredients or steps: the geological succession
had to show evidence of past events; scientists had to accept that the
Earth was older than the historical record; a sense of historical anti-
quity developed through the erection of the geological column; meth-
ods had to be designed to quantify the actual duration of geological
time; and finally scientists had to accept that there was a finite limit of
time. With all of these there came the sense that geological time was
perhaps far longer than hitherto appreciated, that this 'deep time'
could be deciphered through an examination of the rocks, and that
through this a chronology of terrestrial history could be presented and
comprehended.
GENESIS OF THE GEOLOGICAL COLUMN
Without wishing to sound Eurocentric, it can be said that stratigraphic
geology was founded in the tiny geographical area of Britain and parts
of Europe. This region has yielded a largely uninterrupted sequence
through the fossiliferous rocks. However, standard geological nomen-
clature has proved difficult to apply in other parts of the globe: for
example, not all examples of red sandstones found in the United States,
Australia or Asia, can actually be correlated with the red clastic rocks of
Devon, and they may actually occur in different geological Periods.
Today the geological column (see Frontispiece) is divided into
four major divisions or Eons. The earliest is called the Hadean, named
by the American stratigrapher Preston Ercelle Cloud Jr (1912-1991)
after Hades, the hell or underworld of Greek mythology, on account of
the fiery condition of the Earth from its initial formation to the
formation of crustal rocks and the accretion of proto-continents.
Little information on this Eon is known from Earth, but the Moon
has provided a great deal of data on this the earliest 700million years of
our history. Next come the Archean (from the Greek for primitive), the
