
Creationists sometimes point to the Great Unconformity in the Grand Canyon as evidence of Noah’s mythical global flood. But an unconformity is not a layer deposited by a flood. It is a surface representing an interval during which older rocks were exposed, eroded and sometimes deformed before younger sediments were laid on top of them. What is “missing” is not evidence; it is rock that either was never deposited or was subsequently removed, with the surviving rocks preserving evidence of what happened in the intervening time.
Creationists attempts to fit the Grand Canyon into their Biblical flood myth range from the sublime to the ridiculous, none of them in the least plausible and designed to appeal to the parochial ignorance that typifies American creationism. Their conclusion is always sacred and immune to contradiction. Facts are accepted or rejected based on whether they support the conclusion or not. Science, by contrast, starts with a neutral view, collects evidence, then takes a view that accounts for that evidence, as always in science, the facts are neutral and the conclusion provisional, contingent on the discovery of more evidence.
At parts of the Grand Canyon, Cambrian sedimentary rocks rest upon much older Precambrian rocks, leaving more than a billion years of geological history unrepresented by sedimentary strata at that particular location. Far from supporting the idea that the canyon’s rocks were deposited during a single year-long catastrophe, the contact records a succession of events involving sedimentation, burial, tectonic disturbance, uplift, prolonged exposure, erosion and renewed deposition.
A new study published open access in the journal Geology now proposes a mechanism that may explain much of the extraordinary erosion responsible for this gap in the south-western United States. Thomas M. Gernon of the University of Southampton and colleagues have reconstructed a continent-scale escarpment that may have developed along the western margin of Laurentia—the ancient continental core of North America—as the supercontinent Rodinia began breaking apart approximately 800–750 million years ago.







