Only about 400 million years ago did plants and animals leave the water and settle on dry land. The Rhynie Chert, a formation near Aberdeen in northeastern Scotland, holds a trove of well-preserved fossils from the days shortly after that milestone in the history of life. The chert also stars in a Web site sponsored by the University of Aberdeen and aimed at university students.
A geology primer gets you oriented by explaining the formation of the chert at the beginning of the Devonian period. Because the organisms were cloaked by silica from nearby hot springs shortly after their death, fossils preserve incredible detail—sometimes, even the internal structures of cells are visible. Several well-illustrated sections let you meet some of the plants and wee beasties that inhabited the land and adjacent ponds. Asteroxylon, a leafless relative of modern club mosses, is one of the first terrestrial plants and had a vascular system for transporting water and sugars. Arthropods fixed in the chert include spiderlike predators, mites, centipedes, and Heterocrania, a bottom-dwelling, freshwater creature about 15 millimeters long.
Another nice overview of the Rhynie Chert can be found at this site in Germany.