Hadean eon: adhesion: the force of attraction between unlike molecules, or the attraction between the surfaces of contacting bodies. The binding of a cell to another cell, or a cell to a surface, via specific cell adhesion molecules: archean eon: the time from about 3. 8 to 2. 5 billion years ago. During this time the earth had an atmosphere consisting primarily of methane, ammonia, and other gases that would be toxic to most modern life forms. Rocks from the earliest part of the archaean are predominantly volcanic, suggesting that they formed underwater. Fossils preserved in rocks from this period of time include remains of cyanobacteria, the first single-celled forms of life. The cenozoic era is characterized by the formation of modern continents and the diversification of mammals and plants. The climate was warm and tropical toward the beginning of the era and cooled significantly in the second half, leading to several ice ages.