What is the Cambrian Substrate Revolution?
The Cambrian substrate revolution was a crucial evolutionary event which occurred at the dawn of the Cambrian period 542 million years ago. The revolution consisted of the first burrowers to burrow deep into the substrate, rather than grazing at the surface or just below the microbial mats which dominated the sea floor at the time. In fact, the beginning of the Cambrian is internationally defined by the first appearance of Trichophycus pedum, a ubiquitous trace fossil with a distinctive looping pattern. The burrower that made the trace fossil is unknown, but it may have been a slug or a primitive arthropod. Before the Cambrian substrate revolution, the sea floor consisted of a microbial mat on top of a hard, layered, sulphidic, anoxic substrate. Animals lived on the mat, attached to it via holdfasts, grazed the surface of the mat, were embedded in it, or burrowed immediately below it. As the substrate beneath was almost completely anoxic (without oxygen), it was filled with sulfate-red
