The first burrows

Horizontal and then vertical trace fossils appear in late Ediacaran sediments, made by mobile animals with hydrostatic skeletons. Burrowing mixes oxygen and nutrients into sediment that had been locked beneath microbial mats for billions of years — an ecological revolution sometimes called the agronomic revolution. It permanently changed how the seafloor works, and destroyed the mat habitats much of the Ediacaran biota depended on.