CATEGORY: term DEFINITION: An environmental state requiring or using free oxygen in the air for metabolic purposes and which, therefore, causes decay in organic structures. Many materials, including plants, leather, flesh, food remains, and clothing will disintegrate in aerobic conditions.
CATEGORY: term DEFINITION: Without air; the opposite of aerobic. This term is used to describe environmental conditions where oxygen is not present and where decay of organic material is partially or completely stopped. Anaerobic conditions are usually waterlogged but may also occur when a layer or clay, plant, or animal remains is sealed. The remains survive much better than under normal conditions because there is insufficient oxygen for bacterial or fungal growth. The organic materials reach a state of equilibrium beyond which they do not decay.
CATEGORY: fauna DEFINITION: A microscopic, unicellular algae which grow in marine or fresh water and secrete silica skeletons (microfossils) that distinct by species. Their chances of survival are enhanced due to the silica and their deposition in anaerobic conditions. Diatoms can be sampled through deep sea or lake cores. Different species are associated with different habitats, so examples in archaeological deposits can yield information on the changing environment, particularly at coastal sites.
CATEGORY: technique DEFINITION: The study of the remains of fish on archaeological sites, in the form of bones, otoliths, and scales. The latter only survive occasionally in anaerobic conditions, while otoliths have not, to date, been frequently recorded. Fish have markedly different skeletons from mammals. Many fishbones are so small that they appear only in sieving and the bones commonly preserved are the jaws and some other head bones, and the vertebrae. They usually accumulate in refuse deposits and may be interpreted in terms of diet and fishing on the site or in the area that supplied it. Identification of species through comparison with modern fishbones is becoming easier as larger collections of comparative material are built up. When a species has been identified it can lead to evidence for the hydrological conditions around the site; also, the occurrence of the remains of marine species on an inland site has implications for the movement of groups or a trade in fish. A combination of species identification and aging of fish through study of the otoliths can lead to assumptions about the seasonal occupation of certain settlement sites and the subsistence economy of the associated groups.
SYNONYMS OR RELATED TERMS: gleying CATEGORY: geology DEFINITION: A soil horizon characterized by blue, gray, or olive coloring due to excessive moisture in anaerobic conditions; a waterlogging of soil. Gleying may result from a raised water table or from impeded drainage within the soil profile; the latter condition occurs in some podzols. Gley horizons and gley soils are conducive to preservation of organic remains.
SYNONYMS OR RELATED TERMS: gley horizon CATEGORY: geology DEFINITION: The process of waterlogging of soil in which iron is bacterially reduced under anaerobic conditions. Gleying may result from a raised water table or from impeded drainage within the soil profile -- especially in bogs, fens, floodplains, lakes, and swamps. The soil is blue, gray, or olive in coloring and forms gley horizons.
CATEGORY: technique DEFINITION: Any studies of insect remains in an attempt to reconstruct past environments. Pollen analysis and molluscan analysis can reveal information on climate, the environment and, sometimes, the activities of man. Insect remains are usually found in the form of the exoskeleton, parts such as the wing-cases of beetles, and they always come from anaerobic deposits such as ditches, wells, pits, and peat bogs; many of the parts of insects that are species-distinctive do not survive in archaeological deposits. They can be separated from the soilsample by flotation. Insects respond more quickly than plants to climatic change, and may therefore assist in the identification of micro-climatic phases. Insects also have habitat preferences, which is helpful in identifying specific environments.
SYNONYMS OR RELATED TERMS: pollen analysis CATEGORY: related field; technique DEFINITION: The study of fossil and living spores (of lichens and mosses) and pollen (of flowering plants); the technique through which the fossilpollen grains and spores from archaeological sites are studied. The examination of their production, dispersal, and applications is an aid to the reconstruction of past vegetation and climates and developing relative chronologies. Each kind of flowering plant produces pollen that is unique and pollen grains have tough coverings that can last a long time. The resilient exine of the pollen and spores is preserved in anaerobic environments, such as lakes and bogs, and some acidic and dry soils, as in caves. Palynology helps archaeologists find out what plant resources were available to ancient peoples and what the climate was at those times. Palynology was developed by Swedish botanist Lennart von Post.
CATEGORY: geography DEFINITION: An accumulation of dead organic matter, mostly from plants, which becomes preserved mainly by the exclusion of oxygen. It is dark brown or black and partially decomposed, being preserved under anaerobic conditions in an environment of excessive moisture. Peat forms mostly in bogs and fens; the importance of peat to archaeology lies in its preservation of palaeobotanical (palaeoenvironmental) evidence which can be used to reconstruct the ancient environment. The remains can often be radiocarbon dated. Vast beds of this organic fuel occur in Europe, North America, and northern Asia but are worked only where coal is deficient. Peat deposition is the first step in the formation of coal.
SYNONYMS OR RELATED TERMS: palynology CATEGORY: technique DEFINITION: The study of pollen grains in soil samples from an archaeological site which provides information on ancient human use of plants and plant resources. This technique, which is used in establishing relative chronologies as well as in environmental archaeology, was developed primarily as a technique for the relative dating of natural horizons. Pollen grains are produced in vast quantities by all plants, especially the wind-pollinated tree species. The outer skin (exine) of these grains is remarkably resistant to decay, and on wet ground or on a buried surface, it will be preserved, locked in the humus content. The pollen grains of trees, shrubs, grasses, and flowers are preserved in either anaerobic conditions or in acid soils. Samples can be taken from the deposits by means of a core or from individual layers at frequent intervals in a sectionface on an archaeological site. The pollen is extracted and then concentrated and stained and examined under a microscope. Pollen grains are identifiable by their shape, and the percentages of the different species present in each sample are recorded on a pollen diagram. A comparison of the pollen diagrams for different levels within a deposit allows the identification of changes in the percentages of species and thus changes in the environment. As a dating technique, pollen has been used to identify different zones of arboreal vegetation which often correspond to climatic changes. The technique is invaluable for disclosing the environment of early man's sites and can even, over and series of samples, reveal man's influence on his environment by, for example, forest clearance. The sediments most frequently investigated are peat and lake deposits, but the more acid soils, such as podsols, are also analyzed. Radiocarbon dates may be taken at intervals in the sequence, and it is possible to reconstruct the history of vegetation in the area around the site where the samples were taken. Palynology plays an important role in the investigation of ancient climates, particularly through studies of deposits formed during glacial and interglacial stages of the Pleistocene epoch.