Ancient rocks point to an early start for the Great Unconformity

Fresh evidence from rocks in China is contributing to debate about what caused the ‘Great Unconformity’ — a one-billion-year gap in the geological record that exists all over the world. Theories abound: it might have been caused by abrasive worldwide glaciers during a period of ‘Snowball Earth’, or by erosion after the break-up of the supercontinent Rodinia. Tantalisingly, the period precedes a sudden proliferation of life on Earth, known as the Cambrian explosion. But new evidence suggests that most of the erosion that caused the gap happened long before all of that.