Geology Reference
In-Depth Information
Holmes' 'B' Scale
Ages in
Today's values
millions of years
1
Pleistocene
1.6
12
Pliocene
5.1
26
Miocene
24
38
Oligocene
38
58
Eocene
55
-
Palaeocene
65
127
Cretaceous
146
152
Jurassic
208
182
Triassic
245
203
Permian
290
255
Carboniferous
362
313
Devonian
418
350
Silurian
443
430
Ordovician
490
510
Cambrian
544
Holmes' 'B' scale age determinations.
The table compares the age values determined by Holmes for the
base of each geological period, as read from the 'B' curve, with
present day values.
cal age, and the duration of each geological period could be read
directly from the scale.
It was a brave first attempt but, as Holmes had predicted, the
accuracy of Nier's 'most probable ages' did improve with time
and greater sediment thicknesses were discovered elsewhere.
However, the main cause of discrepancy with today's measure-
ments was the age-old problem of the poor geological control
of his five data points. These turned out to be significantly in
error - a di~culty that somewhat undermined their value!
Nevertheless, the 'B' scale, as Holmes called it, enjoyed an unex-
pected success for ten years in a wide variety of scientific fields,
setting a standard that no-one else at the time was able to
 
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