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Palynology is the science of palynomorphs, organic particles between 5 and 500 micrometers in size. Sometimes, but not always, it includes the study of silicaceous or calcareous palynomorphs like diatoms or foraminiferans. The word is derived from Greek and means "strewn or sprinkled forms." Typical palynomorphs are pollen grains, dinoflagellate cysts, spores, ostrocods, phytoliths, acritarchs, chitinozoans and scolecodonts. Other materials studied include particulate organic matter (POM) and kerogen, always found in sedimentary rocks. The palynomorphs may be either contemporary or fossilized and millions or even billions of years old.
Palynology covers the study of many important microfossils. Because of their abundance, some palynomorphs give important clues to dating strata (biostratigraphy) or inferring climactic information about a long-past geologic period. Palynology is considered a branch of earth science and biology, with a focus on micropaleontology and paleobotany. Three useful tools for the palynologist are 1) acids, to burn away inorganic material and reveal palynomorphs, 2) a sieve, to catch particles of the desired size, and 3) a microscope, preferably a powerful scanning electron microscope, to get a detailed image of the palynomorph being studied.
Palynology has made various contributions to the study of Earth's past. For instance, acritarchs, small fossils believed to be mostly algae cysts, are the earliest actual fossils in the fossil record, dating back to as much as two billion years ago, over a billion years before appearance of the first multicellular life. About a billion years ago, acritarchs got larger and more complex, demonstrating evolution in unicellular organisms, and acquired spikes, signaling the first appearance of defense against predation. During the worst Ice Age in Earth's history, the Cryogenian, about 700 million years ago, numerous acritarchs are found, proving that unicellular organisms did just fine during this frigid period.
Two important palynomorphs besides acritarchs are scolecodonts, the jaws of marine chaetognath annelid worms, and chitinozoans, flask-shaped marine palynomorphs of unknown affinity. Scolecodonts give us information about ancient annelids, which otherwise rarely fossilize due to their soft bodies, and are useful biostratigraphic markers due to their rapid evolution and distinctive features.
Some of the first fossil evidence of terrestrial life comes from studies in palynology. A feature found only in pollen from terrestrial plants, called a tetrad, has been located in fossilized pollen dating to the mid-Ordovician, 470 million years ago. This probably came from a plant like liverwort or hornwort, among the first to colonize the land. The first actual macrofossils of plants don't appear in the fossil record until the early Silurian, about 440 million years ago.
Palynology can also be used to catch crooks. If a murderer hides in a bush before or after committing a crime, he might be covered in distinctive pollen from that bush. A palynological test on the suspect's clothes can thus exonerate or condemn them. This is called forensic palynology.