The Great Unconformity is an extraordinarily widespread and highly distinctive erosion surface typically separating crystalline basement rocks of Precambrian age from younger sedimentary strata of shallow marine origin. Several things are remarkable about this erosion surface. Not only is it traceable across North America, Europe, Siberia, Africa and Antarctica, but it also marks the beginning of the Cambrian explosion, which, from an evolutionary perspective, was the time when multicellular animals acquired biomineralized skeletons and underwent a dramatic burst of diversification.
A paper in this week’s Nature suggests the two things are linked. Peters and Gaines present an impressive array of stratigraphic and geochemical data to support the idea that enhanced physical and chemical weathering associated with the formation of the Great Unconformity changed the chemistry of the oceans to such an extent that it acted as the trigger for the evolution of biomineralization and the diversification of Cambrian faunas.
Of course, many creationists also think that the Great Unconformity and the Cambrian explosion are linked, though in a somewhat different manner. They associate the Great Unconformity with the initial transgression of ocean waters onto the continents at the beginning of the global Flood. From this perspective, the fossil-bearing marine sediments overlying the unconformity represent some of the earliest pre-Flood ecosystems overwhelmed at the time of the catastrophe. Whatever our view of origins, the Great Unconformity is clearly a unique geological feature crying out for an explanation involving unique events.
Peters S.E. and Gaines R.R. 2012. Formation of the ‘Great Unconformity’ as a trigger for the Cambrian explosion. Nature 484:363-366.