Plant fossils are important discoveries because they tell us about climatic changes that did or did not support species development over geologic time. They are also important because they are the basis for all carbon based- or "fossil"--fuels including coal, oil and natural gas. As we confront global warming from burning of fossil fuels, the information provided by plant fossils becomes even more important.
Coal
Plant fossils that relate to the Paleozoic/Devonian/Carboniferous geologic age, which occurred about 360 million years ago, make up coal. During the Carboniferous period, a warmer climate allowed for abundant plant life that pulled carbon out of the atmosphere as it grew through photosynthesis. The warmer climate also produced a lot of lakes and lagoons. Over time, plants died and were encapsulated in sediments that were compressed into coal, a most abundant fossil fuel source.
Lycopods were primitive trees that grew up to 100 feet tall and their leaves, stems and trunks make up most coal deposits. Burning of these plant fossils emits the previously trapped carbon into the atmosphere, warming the planet.
Other Plant Fossils
Other plant fossils from different geologic times tell us about the climate of the period during which they grew and offer insights into the development and extinction of species on earth over millions of years. Spore-like fossils like Hornworts occurring about 540 million years ago show us how plant life emerged and colonized land early in the geologic period.
Fern fossils, dating back about 400 million years, like Zosterophyllophytes and Trimerophytes, proliferated in hot swamps, suggesting a global warming period. The geologic record suggests their disappearance correlates to a period of mass extinction and then their reappearance later led to seed plants, like conifers, about 300 million years ago during a more arid climate, and then later flowering plants about 80 million years ago during another warming period.
Plant Fossil Identification
Plant fossil identification can help you generally date the plant to the geologic period in which it originated. For example, spores originated in the Cambrian era; ferns originated in the Devonian era during a warming period; while conifers originated during an arid period.
Most plant fossils are found during the exploration for fuel sources as all fossil fuels are composed of plant material.
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