Why is it difficult to interpret the rock record of Precambrian time?
Rock starta are dated mainly by the type of fossils found in them. Using the Darwinian Evolutionary model, the simpler the type of fossil found in the rocks the older the rock strata is assumed to be.
This is true even in places where the simpler fossils are found on top of the more complex fossils.
During the Cambrian Explosion Nine major phylums are found in the Cambrian rock strata with no procurers found in the strata classified as Pre Cambrian. This lack of fossils makes it very difficult to interpret the rock record of the PreCambrian strata.
Also the PreCambrian strata are assumed to be the oldest rock strata. The older the rock strata the more likely hood that the strata has undergone changes. Erosion, deformation, Volcanic intrusions. and other geological events change the nature of the rocks. These changes make it difficult to interpret what the original nature of the oldest rocks were