A relatively small fraction of the plants and other organisms that live on the Earth at any particular time will ever become fossils. Most dead plant material is decayed by aerobic (oxygen-loving) fungi and bacteria. So, the first requirement for fossilization is that dead plants must be deposited in an environment where air is excluded, that is an anaerobic environment. This usually involves deposition in a body of water (discussed below), but not always. Once deposited, the plants must be buried by sediments so that air is excluded. In addition, these sediments must have enough acidity that anaerobic decay is also reduced.
Paleobotanists are often asked the question, where do you look for fossil plants? The answer is that they typically are found in places where the rocks containing them have been exposed in some way (FIG. 1.8); these rocks may be as far away as the Arctic (FIG. 1.4 ) or the Antarctic. Because streams and rivers cut down through the rocks, exposed strata along waterways are often excellent sites to prospect for fossil plants. Erosion by water in many other places also exposes fossil-bearing rocks. Sometimes it is possible to find plants in eroded cliffs along seashores. In addition to the natural exposure of plant-bearing strata, excavations are frequently the source of many fossils. Road cuts, for example, often reveal fresh surfaces with unweathered rocks that contain well-preserved fossils. As might be expected, quarries and mines are rich sources of fossil plants, revealing rocks that would otherwise have been inaccessible to paleobotanists. Coal balls (FIG. 1.43), a type of permineralization, are frequently encountered in coal mines, and often the shales immediately above the coal seams in such mines contain abundant fossil plants. Quarries in which clay is being excavated for bricks,
tiles, or pottery are sites that often provide fossils. In fact, almost any massive construction site, such as for a dam, a hydroelectric plant, or a building with a deep foundation, can, and has, yielded an abundance of fossil plants.
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