The Great Unconformity is a major gap in Earth’s geologic record. The missing layer between Precambrian and Cambrian rocks represents a gap of around a billion years of history. Among much debate surrounding the cause of the gap, a new study, published in the Proceedings of the National Academy of Sciences, indicates that the timing of the erosion leading to the Great Unconformity aligns with the assembly of the Columbia supercontinent, and that glaciation only contributed minimally.
The origin of the Great Unconformity is debated among geologists. Some believe evidence points to the ancient glaciation associated with “snowball Earth,” which occurred around 700 million years ago, is to blame. Others think tectonic processes associated with Columbia and Rodinia supercontinent cycles are the main cause.
The Great Unconformity was first recognized in the layers of the Grand Canyon, and many subsequent studies took place there to attempt to determine a cause. Those studies showed variable timing and mechanisms. The authors of the new study think that the evidence for Neoproterozoic-period snowball Earth glaciation causing the unconformity at such large scales is weak.








