- By the early years of the twentieth century, as the geology of the continents began to be better known, it was realized that Permian and Precambrian glacial deposits occur virtually on all continents and at low latitudes.
- Plenty of suitable sedimentary deposits exist within the late Precambrian and Cambrian strata.
- The crest of the Blue Ridge is usually underlain with Precambrian or Cambrian igneous rocks.
The Precambrian extended from the origin of the earth (believed to have been about 4,600 million years ago) to about 570 million years ago, representing nearly ninety per cent of geological time. The oldest known Precambrian rocks have been dated to about 3,800 million years old, and the earliest living organisms date from the latter part of the aeon. The Precambrian is now replaced in formal stratigraphic schemes by the Archaean, Proterozoic, and (in some schemes) Priscoan aeons.
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