Phytoliths (from Greek, "plant stone") are rigid, microscopic structures made of silica, found in some plant tissues and persisting after the decay of the plant. These plants take up silica from the soil, whereupon it is deposited within different intracellular and extracellular structures of the plant. Phytoliths come in varying shapes and sizes. Although some use "phytolith" to refer to all mineral secretions by plants, it more commonly refers to siliceous plant remains. In contrast, mineralized calcium secretions in cacti are composed of calcium oxalates.
There is still debate in the scientific community as to why plants form phytoliths, and whether silica should be considered an essential nutrient for plants. Studies that have grown plants in silica-free environments have typically found that plants lacking silica in the environment do not grow well. For example, the stems of certain plants will collapse when grown in soil lacking silica. In many cases, phytoliths appear to lend structure and support to the plant, much like the spicules in sponges and leather corals. Phytoliths may also provide plants with protection. These rigid silica structures help to make plants more difficult to consume and digest, lending the plant's tissues a grainy or prickly texture. Phytoliths also appear to provide physiologic benefits. Experimental studies have shown that the silicon dioxide in phytoliths may help to alleviate the damaging effects of toxic heavy metals, such as aluminum. Finally, calcium oxalates serve as a reserve of carbon dioxide. Cacti use these as a reserve for photosynthesis during the day when they close their pores to avoid water loss; baobabs use this property to make their trunks more flame-resistant.
First, soluble silica, also called monosilicic acid, is taken up from the soil when plant roots absorb groundwater. From there, it is carried to other plant organs by the xylem. By an unknown mechanism, which appears to be linked to genetics and metabolism, some of the silica is then laid down in the plant as silicon dioxide. This biological mechanism does not appear to be limited to specific plant structures, as some plants have been found with silica in their reproductive and sub-surface organs.
Phytoliths are composed mainly of noncrystalline silicon dioxide, and about 4% to 9% of their mass is water. Carbon, nitrogen, and other major nutrient elements comprise less than 5%, and commonly less than 1%, of phytolith material by mass. These elements are present in the living cells in which the silica concretions form, so traces are retained in the phytoliths. Such immobilised elements, in particular carbon, are valuable in that they permit radiometric dating in reconstructing past vegetation patterns. The silica in phytoliths has a refractive index ranging from 1.41 to 1.47, and a specific gravity from 1.5 to 2.3. Phytoliths may be colorless, light brown, or opaque; most are transparent. Phytoliths exist in various three-dimensional shapes, some of which are specific to plant families, genera or species.
Phytoliths may form within single cells, or multiple cells within a plant to form 'conjoined' or multi-cell phytoliths, which are three-dimensional replicas of sections of plant tissue. Conjoined phytoliths occur when conditions are particularly favourable for phytolith formation, such as on a silica rich substrate with high water availability
Families where phytolith production is rare or not observed:
Phytoliths are very robust, and are useful in archaeology because they can help to reconstruct the plants present at a site when the rest of the plant parts have been burned up or dissolved. Because they are made of the inorganic substances silica or calcium oxalate, phytoliths don't decay with the rest of the plant and can survive in conditions that would destroy organic residues. Phytoliths can provide evidence of both economically important plants and those that are indicative of the environment at a particular time period.
Phytoliths may be extracted from residue on many sources: dental calculus (buildup on teeth); food preparation tools like rocks, grinders, and scrapers; cooking or storage containers; ritual offerings; and garden areas.
The first step in the laboratory analysis of phytolith samples is processing, in order to extract the phytoliths from the soil. Phytoliths can be extracted from soil samples in two ways: chemically or by ashing. After processing, microscopy is used to identify the phytoliths. Optical microscopes with magnifications of 200-400x are typically used to screen phytoliths. Scanning electron microscopy may also allow for a more detailed study of phytoliths.
Taxonomic resolution issues deriving from the multiplicity and redundancy problems can be dealt with by integrating phytolith analysis with other areas, such as micromorphology and morphometric approaches used in soil analysis. It is suggested that using phytolith data from food residues (on ceramics, usually) can decrease the bias from both of these problems, because phytolith analysis is more likely to represent crop products and identification of phytoliths can be made with more confidence. Also, food residues do not usually accumulate extraneous deposits. In other words, the samples are more likely to represent a primary context.
Phytoliths occur abundantly in the fossil record, and have been reported from the Late Devonian onwards. Robustness of phytoliths make them available to be found in various remains including sedimentary deposits, coprolites, and dental calculus from diverse environmental conditions. In addition to reconstructing human-plant interactions since the Pleistocene, phytoliths can be used to identify palaeoenvironments and to track vegetational change. More and more studies are acknowledging phytolith records as a valuable tool for reconstructing pre-Quaternary vegetation changes (e.g.,). Occasionally, paleontologists find and identify phytoliths associated with extinct plant-eating animals (i.e. herbivores). Findings such as these reveal useful information about the diet of these extinct animals, and also shed light on the evolutionary history of many different types of plants. Paleontologists in India have recently identified grass phytoliths in dinosaur dung (coprolites), strongly suggesting that the evolution of grasses began earlier than previously thought.
Phytolith records in the context of the global silica cycle, along with CO2 concentrations and other paleoclimatological records, can help constrain estimates of certain long-term terrestrial, biogeochemical cycles and interrelated climate changes.
Light intensity (e.g., open versus closed canopies) can affect cell morphology, especially cell length and area, which can be measured from phytolith fossils. These can be useful for tracing fluctuations in the ancient light regime and canopy cover.
Freshwater oases and related landscape changes that could have affected plant-human interactions were reconstructed through synthesizing phytolith, pollen, and paleoenvironmental data in the well-known early hominin site of Olduvai Gorge in Tanzania.
Comparisons between paleorecords of phytolith remains and modern reference remains in the same region can aid reconstructing how plant composition and related environments changed over time.
Though further testing is required, evolution and development of phytoliths in vascular plants seem to be related to certain types of plant-animal interactions in which phytoliths function as a defensive mechanism for herbivores or related to adaptive changes to habitats.
Japanese and Korean archaeologists refer to grass and crop plant phytoliths as "plant opal" in archaeological literature.
For extended examples of phytolith taxonomy, see the University of Sheffield's comprehensive Phytolith Interpretation page.
Research, particularly since 2005 has shown that carbon in phytoliths can be resistant to decomposition for millennia and can accumulate in soils. While researchers had previously known that phytoliths could persist in some soils for thousands of years  and that there was carbon occluded within phytoliths that could be used for radiocarbon dating, research into the capacity of phytoliths as a method of storing carbon in soils was pioneered by Parr and Sullivan  suggested that there was a real opportunity to sequester carbon securely in soils for the long term, in the form of carbon inclusions in durable silica phytoliths. Subsequent research has shown the effectiveness of phytoliths as a process to sequester carbon using a range of agricultural crops and other economically important plants. While carbon sequestration is a potentially important way to limit atmospheric greenhouse gas concentrations in the long term, the use of phytoliths to achieve this must be balanced against other uses that might be made of the same biomass carbon (or land for producing biomass) to reduce GHG emissions by other means including, for example, the production of bioenergy to offset fossil fuel emissions. If enhanced phytolith production results in a reduced availability of biomass for other GHG mitigation strategies, its effectiveness for lowering net GHG emissions may be reduced or negated.
Deborah M. Pearsall (born 1950) is an American archaeologist who specializes in paleoethnobotany. She maintains an online phytolith database. She is a full professor in the Department of Anthropology at the University of Missouri in Columbia, Missouri, where she first began working in 1978. She received her Ph.D. in anthropology from the University of Illinois at Urbana-Champaign in 1979, with a dissertation entitled The Application of Ethnobotanical Techniques to the Problem of Subsistence in the Ecuadorian Formative.
Pearsall was awarded the 2002 Fryxell Award for Exceptional Interdisciplinary Research by the Society for American Archaeology.Dolores Piperno
Dolores Piperno is an American archaeologist specializing in archaeobotany. She is a senior scientist emeritus of the Smithsonian Tropical Research Institute in Balboa, Panama and the Smithsonian National Museum of Natural History, Washington.Erella Hovers
Erella Hovers (born 1956) is an Israeli paleoanthropologist. She is currently a professor at The Hebrew University of Jerusalem, working within the Institute of Archeology. The majority of her field work is centered in the Horn of Africa, with a primary focus on Ein Qashish, Israel and Eastern Ethiopia. Her research concentrates on the development of the use of symbolism during the Levantine Middle Palaeolithic and Middle Stone Age. Other research interests include lithic technology, taphonomy, and general behavior of early hominids..Fosters Site
The Fosters Site, designated 20SA74, is an archaeological site located near Bridgeport, Michigan. It was listed on the National Register of Historic Places in 1982.Fosters Site, located beside the Flint River, is the site of a village dating from the Late Woodland period. The village was likely seasonally occupied in the fall and winter. It was excavated in 1967 by researchers from the University of Michigan Museum of Archaeology, who found ceramic shards, triangular weapon points, and fish and plant remains.HaYonim Cave
HaYonim Cave (Hebrew: מערת היונים, Me'arat HaYonim, lit. Cave of the Pigeons) is a cave located in a limestone bluff about 250 meters above modern sea level, in the Upper Galilee, Israel.Hatula
Hatula is an early Neolithic archeological site in the Judean hills south of Latrun, beside Nahal Nachshon, in Israel, 20 kilometres (12 mi) west of Jerusalem. The site is 15 metres (49 ft) above the riverbed on a rocky slope in an alluvial valley. Excavations revealed three levels of occupation in the Natufian, Khiamian and PPNA (Sultanian).The site was excavated in eight seasons between 1981 and 1990 by Monique Lechevallier of the CNRS and Avraham Ronen from the University of Haifa. They unearthed a semi-circular dwelling with burial in the latest period. The site was suggested to have been a hunting station for flocks of gazelle. Radiocarbon dates for the site suggest habitation between 10150 and 9320 BC by semi-sedentary groups. Evidence suggested domesticated dogs were present at the site. Study of the lithic industry suggested the Khiamian was an adaptation of the Natufian in the area. Evidence of an accomplished bone industry were found but no signs of any grinding tools, art objects or building materials in the earliest two levels indicating a short term settlement pattern.Archeaobotanical samples were taken from the Khiamian and Sultanian periods for phytolith analysis. This gave evidence of wheat at the site, along with an unidentified grass whose seeds were possibly a food source, both of which suggested that cereals may have been part of the Natufian economy in Hatula. Changes in morphology of cells from husks of the grasses suggest a larger seed content, possibly due to increased exploitation, in the Sultanian.Idioblast
An idioblast is an isolated plant cell that differs from neighboring tissues. They have various functions such as storage of reserves, excretory materials, pigments, and minerals. They could contain oil, latex, gum, resin, tannin or pigments etc. Some can contain mineral crystals such as acrid tasting and poisonous calcium oxalate or carbonate or silica.
Any of the tissue or tissue systems of plants can contain idioblasts.
Idioblasts are divided into three main categories: excretory, tracheoid, and sclerenchymatous.
Idioblasts can contain biforine cells that form crystals. The chemicals are excreted by the plant and stored in liquid or crystalline form. In bundles they are known as druse and as crystals they can be of raphide [needle] form. When the end of an idioblast is broken the crystals or other substance is ejected by internal water pressure. Idioblasts of calcium oxalate may function as a deterrent to herbivores, as a means of sequestering or storing calcium, or as a means of stiffening tissue structure.Irwin Rovner
Irwin Rovner (born 1941) is an American archaeologist who initiated the study and use of phytoliths in archaeology. He is retired from the faculty of North Carolina State University. Rovner is CEO of Binary Analytical Consultants, which provides expert vision and computer-assisted morphometric analysis of micro- and macro- remains and artifacts in support of archaeological investigations.Las Vegas culture (archaeology)
The Las Vegas culture is the name given to a large number of Holocene settlements which flourished between 8000 BCE and 4600 BCE.(10,000 to 6,600 BP) near the coast of present-day Ecuador. The name comes from the location of the most prominent settlement, Site No. 80, near the Las Vegas River and now within the city of Santa Elena. The Las Vegas culture represents "an early, sedentary adjustment to an ecologically complex coastal environment."The Las Vegas culture is important because it was one of the earliest cultures in South America to practice agriculture.Leersia oryzoides
Leersia oryzoides is a species of grass known by the common name rice cutgrass or just cut-grass. It is a widespread grass native to Europe, Asia, and North America and present in many other regions, such as Australia, as an introduced species. This is a rhizomatous perennial grass growing to a maximum height between 1 and 1.5 meters. The leaves are up to about 28 centimeters long and have very rough, minutely toothed edges. The inflorescence is a loose, open array of wavy, hairlike branches bearing rows of spikelets. Each spikelet is a flat fruit with a rough, bristly lemma without an awn, and no glumes. Some of the spikelet branches develop within the sheaths of the leaves and are cleistogamous. This grass is sometimes used for erosion control and restoring wetlands.Merychippus
Merychippus is an extinct proto-horse of the family Equidae that was endemic to North America during the Miocene, 15.97–5.33 million years ago. It had three toes on each foot and is the first horse known to have grazed.New World crops
The phrase "New World crops" is usually used to describe crops, food and otherwise, that were native to the New World (mostly the Americas) before 1492 CE and not found anywhere else at that time. Many of these crops are now grown around the world and have often become an integral part of the cuisine of various cultures in the Old World.
Notable among these crops are the Three Sisters: maize, winter squash, and climbing beans.Paleoethnobotany
Pal(a)eoethnobotany or Archaeobotany is the archaeological sub-field that studies plant remains from archaeological sites. Basing on the recovery and identification of plant remains and the ecological and cultural information available for modern plants, the major research themes are the use of wild plants, the origins of agriculture and domestication, and the co-evolution of human-plant interactions.Paleosol
In the geosciences, paleosol (palaeosol in Great Britain and Australia) can have two meanings. The first meaning, common in geology and paleontology, refers to a former soil preserved by burial underneath either sediments (alluvium or loess) or volcanic deposits (volcanic ash), which in the case of older deposits have lithified into rock. In Quaternary geology, sedimentology, paleoclimatology, and geology in general, it is the typical and accepted practice to use the term "paleosol" to designate such "fossil soils" found buried within either sedimentary or volcanic deposits exposed in all continents as illustrated by Rettallack (2001), Kraus (1999), and other published papers and books.
In soil science, paleosols are soils formed long periods ago that have no relationship in their chemical and physical characteristics to the present-day climate or vegetation.
Such soils form on extremely old continental cratons and as small scattered localities in outliers of ancient rock.Post-excavation analysis
Post-excavation analysis constitutes processes that are used to study archaeological materials after an excavation is completed. Since the advent of "New Archaeology" in the 1960s, the use of scientific techniques in archaeology has grown in importance. This trend is directly reflected in the increasing application of the scientific method to post-excavation analysis. The first step in post-excavation analysis should be to determine what one is trying to find out and what techniques can be used to provide answers. Techniques chosen will ultimately depend on what type of artifact(s) one wishes to study. This article outlines processes for analyzing different artifact classes and describes popular techniques used to analyze each class of artifact. Keep in mind that archaeologists frequently alter or add techniques in the process of analysis as observations can alter original research questions.In most cases, basic steps crucial to analysis (such as cleaning and labeling artifacts) are performed in a general laboratory setting while more sophisticated techniques are performed by specialists in their own labs. The sections of this article describe specialized techniques and section descriptions assume that artifacts have already been cleaned and cataloged.Shijiahe culture
The Shijiahe culture (2500–2000 BC) was a late Neolithic culture centered on the middle Yangtze River region in Shijiahe Town, Tianmen, Hubei Province, China. It succeeded the Qujialing culture in the same region and inherited its unique artefact of painted spindle whorls. Pottery figurines and distinct jade worked with advanced techniques were also common to the culture.Songze culture
The Songze Culture was a Neolithic culture that existed between 3800 and 3300 BCE in the Lake Tai area near Shanghai.Theopetra cave
The Theopetra cave is located in Thessaly, Greece, on the north-east side of a limestone rock formation, 3 km (2 mi) south of Kalambaka. The site has become increasingly important as human presence is attributed to all periods of the Middle and Upper Paleolithic, the Mesolithic, Neolithic and beyond, bridging the Pleistocene with the Holocene.