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How Do We Know?
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Palynology is the study of pollen. Scientists at the Illinois State Museum study fossil pollen that has been preserved in peats and lake sediments. Pollen preserves best if the sedimentary environment lacks oxygen or is acidic, conditions unfavorable for the organisms that decompose pollen. Fossil pollen is an important kind of data for reconstructing past vegetation. Because vegetation is sensitive to climate, fossil pollen is a very important kind of proxy data for reconstructing past climates.
Most plants are either insect pollinated or wind pollinated. In insect pollinated plants, insects, especially bees, transport pollen from one flower to the other. Because the insect vector of pollen transport is highly efficient, insect pollinated plants produce relatively less pollen and little of this pollen is released into the air. On the other hand, wind-pollinated plants produce large amounts of pollen because the probability is small that an individual pollen grain will actually land on another flower of the same species. Many of our forest trees are wind pollinated, as well as important prairie plants such as grasses, ragweed, and sage. Some insect pollinated plants do release significant amounts of pollen into the atmosphere, and pollen from these plants is also important for reconstructing past vegetation.
Because of their very small size, pollen grains, which are living plants, are easily dried out and destroyed. Thus, they have evolved a very tough and resistant outer "shell," which preserves well and which enables the scientist to concentrate the pollen for study. Some pollen eventually falls into lakes or peatlands where it accumulates with other sediments, layer after layer, year after year. Lake sediments typically lack oxygen necessary for decomposing organisms, and if the sediment remains wet, the pollen will preserve for thousands or even millions of years.
Pollen is an especially valuable kind of fossil for reconstructing past environments for a number of reasons:
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