Relative dating of rock strata

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 on the basis of their positions in an outcrop and their fossil content.

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In short, was correlation among these various sites now possible?Inherent in many of the assumptions underlying the early attempts at interpreting natural phenomena in the latter part of the 18th century was the ongoing controversy between the biblical view of Earth processes and history and a more direct approach based on what could be observed and understood from various physical relationships demonstrable in nature.A substantial amount of information about the compositional character of many rock sequences was beginning to accumulate at this time., a scholar of wide repute and following from the School of Mining in Freiberg, Germany, was very successful in reaching a compromise between what could be said to be scientific “observation” and biblical “fact.” Werner’s theory was that all rocks (including the sequences being identified in various parts of Europe at that time) and the Earth’s topography were the direct result of either of two processes: (1) deposition in the primeval ocean, represented by the Noachian flood (his two “Universal,” or Primary, rock series), or (2) sculpturing and deposition during the retreat of this ocean from the land (his two “Partial,” or disintegrated, rock series).While making use of Steno’s principle of superposition, Lehmann recognized the existence of three distinct rock assemblages: (1) a successionally lowest category, the Primary (Urgebirge), composed mainly of crystalline rocks, (2) an intermediate category, or the Secondary (Flötzgebirge), composed of layered or stratified rocks containing fossils, and (3) a final or successionally youngest sequence of alluvial and related unconsolidated sediments (Angeschwemmtgebirge) thought to represent the most recent record of the Earth’s history.

This threefold classification scheme was successfully applied with minor alterations to studies in other areas of Europe by three of Lehmann’s contemporaries.Did they record the same series of geologic events in the Earth’s past?Were the various layers at each site similar to those of other sites?Although Steno’s principles were being widely applied, there remained to be answered a number of fundamental questions relating to the temporal and lateral relationships that seemed to exist among these disparate European sites.Were these various German, Italian, and Russian sites at which Lehmann’s threefold rock succession was recognized contemporary?In the correct spirit but for the wrong reasons, , Egypt, were the preserved remains of discarded lentils left behind by the builders of the pyramids.