Radiometric dating is a complex process complicated by
age and history of Earth’s rocks and rock assemblages.
Such time determinations are made and the record of past geologic events is deciphered by studying the distribution and succession of rock strata, as well as the character of the fossil organisms preserved within the strata.
In spite of this deductive approach to interpreting natural events and the possibility that they might be preserved and later observed as part of a rock outcropping, little or no attention was given to the history—namely, the sequence of events in their natural progression—that might be preserved in these same rocks.
, a seminal work that laid the essential framework for the science of geology by showing in very simple fashion that the layered rocks of Tuscany exhibit sequential change—that they contain a record of past events.
The tracing and matching of the fossil content of separate rock outcrops (i.e., correlation) eventually enabled investigators to integrate rock sequences in many areas of the world and construct a relative geologic time scale.
His Primary and Secondary divisions are roughly similar to Lehmann’s Primary and Secondary categories.Earth’s surface is a complex mosaic of exposures of different rock types that are assembled in an astonishing array of geometries and sequences.Individual rocks in the myriad of rock outcroppings (or in some instances shallow subsurface occurrences) contain certain materials or mineralogic information that can provide insight as to their “age.”For years investigators determined the relative ages of sedimentary rock strata on the basis of their positions in an outcrop and their fossil content.According to a long-standing principle of the geosciences, that of superposition, the oldest layer within a sequence of strata is at the base and the layers are progressively younger with ascending order.The relative ages of the rock strata deduced in this manner can be corroborated and at times refined by the examination of the fossil forms present.