Precambrian Era The Precambrian era laster 4600-541 million years ago. During this time, there were no plant life on the planet. Most of the things that were on the planet were rocks. The most common type of rock was Isua greenstone. Most rocks have been eroded away, subducted, or metamorphosed. During this time, the atmospheres and oceans were formed, plate tectonics began to build up continental masses. The air during this time was mostly made up of water vapor, carbon dioxide, and nitrogen.
The Evolution of Animals Eukaryotes come in two grades of organization: single-celled (protists) and multicellular (plants, animals, and fungi). The world today is full of complex multicellular plants and animals: how, why, and when did they evolve from protists? Proterozoic Protists A single-celled eukaryote or protist can carry chlorophyll (it can be an autotrophic, photosynthetic, "alga"), it can eat other organisms (it can be an organotrophic, "protozoan" "animal"), or it may do both