Early plants made Earth muddier. Ancient riverbed deposits of mud rock — rocks containing bits of clay and silt smaller than grains of sand — began increasing around 458 million years ago, around the time that rootless plants became common across Earth, researchers say.
Anecdotally, geologists have long noted that early sediment deposits became muddier at some point, and suggested a connection with plants (SN: 6/22/74, p. 398). But no one had ever pinpointed when that muddening happened.