Fossilized Plants include roots, tree trunks, leaves, amber (sap or tree resin), cones, seeds, fruit, pollen, and spores. Fossil plants have been found in various environments throughout the world various terrestrial settings as well as marine shore, tidal flats, swamps and other semiaquatic areas. Throughout the Geologic Time Scale, especially during the Carboniferous Period , many plant species are used as “Index Fossils” indicating specific Geologic Time Periods in sedimentary rock. The earliest form of plant life known is the Blue-green Algae formed and found from the Pre-Cambrian Period . The earliest recorded single cell plant life fossilization discovered dates back to about 1 Billion years ago.
The Ordovician Period dating back to about 500 million years ago denotes development of the embryophytes group of plants. These multicellular vascular land plants had primitive leaf and root systems. The fossilized plant record from the Silurian Period (430 Million Years ago) show plants preserved such as the lycophyte Baragwanathia longifolia . This primitive vascular plant was un-branched with spiky leaves and shallow roots. The plants of this time lacked seeds and were non-flowering.
The Devonian Period experienced the evolution of what many believe to be the first modern tree, Archaeopteris (Ancient Fern). Archaeopteris is an extinct plant genus with a wood trunk, fern-like leaves. It was a non-flowering and non-seed producing species of flora. This useful index fossil is found in strata dating from the Upper Devonian to the Lower Carboniferous.
During the Mississippian and Pennsylvanian Periods , known as the Carboniferous Period great forests of Lepidodendron trees (scale trees) were abundant and great forests of these types of trees arose. These trees grew in some cases up to 100 feet and the surface of their trunk looked much like the pineapple of today. Their leaves grew straight up somewhat like the fronds of the cactus. This period is where the great abundance of plant life over millions of years gave rise to the coal seams found today.
Petrified wood which is common in many parts of the world is found in desert and arid areas of the world where the land is easily eroded and is readily exposed. Petrified wood has been found on all continents of the world. The process of wood petrification is the replacement of the organic wood cells and fibers with inorganic minerals such as calcium carbonate, soluble silica materials and precipitated salts.
By the Late Devonian Period tall trees and a wide variety of plants diversified and became widely abundant. This abundance gave way to the development of vast forests with shrubs, low lying plants and tall trees. Following the Permian Extinction and well into the Triassic Period (about 210 Million years ago) the flowering plants developed and took a firm hold toward future development and great diversification and climatic adaption .
Flowering Plants embarked on a massive explosion of abundance and diversity in the Cretaceous and Tertiary Periods leading to many of the plant species still in existence today. Finally about 45 million years ago during the Tertiary Period the grasses developed on the vast open plains probably due to the previous extinctions of ancient trees. The wide open areas of space gave way to major groups of primitive grasses to develop, evolve and spread. During the Late Tertiary Period from approximately 10 million years ago, many climatic changes such as temperature drops, temperature increases, fluctuation of O2 and CO2 levels took place. Throughout this time period the grasses the world over adapted, evolved, spread and now are a major part of various ecosystems throughout the world.