Paleobotany, the study of the geologic history of the plant kingdom, is a major branch of paleontology, the study of ancient life. The most ancient fossils yet discovered, those of the Aecheozoic Era, are over 3 billion years old and are evidently allied to microscopic plants of simple form. The study of the origins and development of all plants and planlike organisms, from yeasts and bacteria to redwoods and orchids, from these ancient beginnings is included in the science of pleobotany. Study of microscopic plant fossils, particularly pollen, has grown into an important specialization known as palynology.
Adolphe Brongniart (1801 – 76) pioneered the use of plant fossils for geologic age determination. Important contributions to 19th century paleonbotany were also made by W.C. Williamson, who studied calcareous concretions called coal balls in which plant tissue structures were preserved in almost perfect condition. Early in the 1900s, A.C. Seward made very important contributions to Gondwana paleobotany and to recognition of floristic diversifications. Modern research has been amplified by extensive palynologic investigations of sediments of all ages.
The advent of Precambrian (Proterozoic and Archeozoic eras) paleobotany is one of the most significant recent developments. In 1965, E.S Barghoorn established the existence of well preserved, divesified blue green algae in chert deposits of the Gunflint Formation of Ontario, approximately 1.9 billion years old. Later studied have demonstrated similar fossil algae in a large number of other similar deposits, mostly associated with calcareous or sometimes siliceous algal structures called stromatolites. These occurrences are likely to provide a basis for paleontological age determination during the later Precambrian (Proterozoic). Such a result would have been unthinkable a generation ago when all suggestions of Precambrian fossils were greeted skeptically. These results have far reaching biological implications about the antiquity of life on Earth and the origin of nucleated. The immensity of Precambrian research potential is indicated by the fact that Precambrian time represented approximately 7/8 of the history of the Earth.