Reference work entry
Plants were the earliest life on Earth. Fossils of blue algae and fugus have been found in 3.5-billion-year-old Archaean rocks. Primitive bacteria and algae developed in the Archaean and early Proterozoic, and marine algae developed from the Middle Proterozoic to the Ordovician. Terrestrial spore-bearing plants developed from the Silurian to the Carboniferous, and gymnosperms developed from the Permian to the Jurassic. Angiosperms prospered in the Cretaceous and Cenozoic. Plant fossils are key indicators used to identify and classify ancient continents, climatic regions and biogeographic regions. Ancient plants were also involved in mineral and rock formation. For example, the formation of Archaean sedimentary iron ore was related to ferro-bacteria activity. Various types of algae can form reef limestone, boghead coal and diatomite. Lower plants are associated with the formation of crude oil and oil shale, whereas higher plants are the basis for the formation of coal seams (Fig. 22).
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