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Stone Age

Stone Age

The Stone Age is a broad prehistoric time period during which humans widely used stone for toolmaking. Stone tools were made from a variety of different kinds of stone. For example, flint and chert were shaped (or chipped) for use as cutting tools and weapons, while basalt and sandstone were used for ground stone tools, such as quern-stones. Wood, bone, shell, antler and other materials were widely used, too. During the most recent part of the period, sediments (like clay) were used to make pottery. A series of metal technology innovations characterize the later Chalcolithic (Copper Age), Bronze Age and Iron Age. The period encompasses the first widespread use of technology in human evolution and the spread of humanity from the savannas of East Africa to the rest of the world. It ends with the development of agriculture, the domestication of certain animals and the smelting of copper ore to produce metal. It is termed prehistoric, since humanity had not yet started writing -- the traditional start of history (i.e., recorded history). The term "Stone Age" was used by archaeologists to designate this vast pre-metallurgic period whose stone tools survived far more widely than tools made from other (softer) materials. It is the first age in the three-age system and was subdivided into the Palaeolithic, Mesolithic and Neolithic periods, by John Lubbock in his now classic 1865 book Pre-historic Times. These three periods are further subdivided. In reality, the succession of phases differs enormously from one region (and culture) to another, indeed, humanity continued to expand into new areas even during the metal ages. Therefore, it is better to speak of a Stone Age, instead of the Stone Age.

The Stone Age in archaeology

culture] The date range of this period is ambiguous, disputed, and variable according to the region in question. While it is possible to speak of a general 'stone age' period for the whole of humanity, some groups never developed metal-smelting technology, so remained in a 'stone age' until they encountered technologically developed cultures. However, in general, it is believed that this period began somewhere around 3 million years ago, starting with the first hominid tool-making in Africa. Most australopithecines probably did not use stone tools (although they seem to be invented by Paranthropus robustus) but the study of their remains still falls within the remit of archaeologists studying the period. Due to the prevalence of stone artefacts, which are frequently the only remains which still exist, lithic analysis is a major, and specialised, form of archaeological investigation for the period. This involves the measurement of the stone tools to determine their typology, function and the technology involved. This frequently involves an analysis of the lithic reduction of the raw materials, examining how the artefacts were actually made. This can also be examined through experimental archaeology, by attempting to create replica tools. This is done by flintknappers who reduce flintstone to a flint tool.

Modern use of the term

flint tool One problem with the term is that it implies that human advancement and time periods in prehistory are only measured by the type of tool material most widely used, rather than, for example, type of social organisation, food sources exploited, or adaption to harsh climates. This is a product of the level of knowledge of the distant past during the nineteenth century when the three age system was developed, a time when finds of artefacts were the main goal of an archaeological excavation. Modern archaeological techniques stress a wider collection of information that has expanded our knowledge of prehistory and rendered neat divisions such as the term 'Stone Age' increasingly obsolete. We now know that the changes in past societies over the millennia were complex and involved multiple factors such as the adoption of agriculture, settlement or religion and that tool use is just one unrepresentative indicator of a society's practices and beliefs. Another problem connected with the term Stone Age is that it was created to describe the archaeological cultures of Europe, and that it is inconvenient to use it in relation to regions such as some parts of the Americas and Oceania, where farmers or hunter-gatherers used stone for tools until European colonisation began. Metal-working was a much less important part of people's lives there and it is more useful to use other terms when dividing prehistory in those areas. The same incongruence applies to the Iron Age worldwide, because in the Americas iron (but not copper, silver or gold) was unknown until 1492, in Oceania until the 17th century. A Stone Age was usually followed by a Bronze Age, during which metalworking technology allowed bronze (copper and tin or other metals) tools to become more common. The transition out of the Stone Age occurred between 6000 BC and 2500 BC for much of humanity living in North Africa, Asia and Europe. In some regions, such as Subsaharan Africa, the Stone Age was followed directly by an Iron Age. It is generally believed that the Middle East and southeastern Asian regions progressed past Stone Age technology around 6000 BC. Europe, and the rest of Asia became post-Stone Age societies by about 4000 BC. The proto-Inca cultures of South America continued at a Stone Age level until around 2000 BC, when gold, copper and silver made their entrance, the rest following later. Australia remained in the Stone Age until the 17th century. We also now know that the transition from a Stone Age to a Bronze Age was not a neat switch but a long, gradual process involving the working of gold and copper at what are technically Neolithic sites. This "transition" period is known as the Copper age or Chalcolithic. It was a short and more a regional development, because alloying tin with copper began quite soon, except in regions lacking tin. Ötzi the Iceman for instance, a mummy from about 3300 BC carried with him a copper axe and a flint knife. Stone tool manufacture also continued long into the succeeding metal-using ages, possibly even until the Early Middle Ages. In Europe and North America, millstones were in use until deep the 20th century, and still are in many parts of the world.

Human development during the Stone Age

The Stone Age covers an immense time span, and during this period major climatic and other changes occurred, which affected the evolution of humans. Humans themselves evolved into their current morphological form during the later period of the Stone Age. See also: Human evolution

Palaeolithic

The Old Stone Age period runs from about 2 million years ago to the end of the Pleistocene, 10,000 years ago. For areas with an early neolithisation, the Palaeolithic includes the Epipalaeolithic, and ends around 8,000 years ago.

Lower Palaeolithic

Near the end of the Pliocene epoch in Africa, an early ancestor of modern humans, called Homo habilis, developed the earliest known stone tools. These were relatively simple tools known as choppers. Homo habilis is presumed to have mastered the Oldowan era tool case which utilized stone flakes and cores. This industry of stone tools is named after the site of Oldupai Gorge in Tanzania. These humans likely subsisted on scavenged meat and wild plants, rather than hunted prey. Around 1.5 million years ago, a more evolved human species, Homo erectus, appeared. H. erectus learnt to control fire and created more complex chopper tools, as well as expanding out of Africa to reach Asia, as shown by sites such as Zhoukoudian in China. By 1 million years ago, the earliest evidence of humans in Europe is known, as well use of the more advanced handaxe tool.

Middle Palaeolithic

handaxe This period began about 200,000 years ago and is most well-known as being the era during which the Neanderthals lived (c. 120,000–35,000 years ago). The stone artefact technology of the Neanderthals is generally known as the Mousterian. The Neanderthals eventually disappeared from the archaeological record, replaced by modern humans who first appeared in southern Africa around 100,000 years ago. Although often identified in the public's mind as primitive, there is evidence that Neanderthals nursed their elderly and practised ritual burial indicating an organised society. The earliest evidence of settlement in Australia dates to around 40,000 years ago when modern humans likely crossed from Asia by hopping from island to island. Middle Palaeolithic peoples demonstrate the earliest evidence for art and other expressions of abstract thought such as ochre body decoration.

Upper Palaeolithic

ochre is an example of Upper Palaeolithic culture]] From 35,000 to 10,000 years ago (the end of the last ice age) modern humans spread out further across the Earth during the period known as the Upper Palaeolithic. After the arrival of the first modern humans (Cro-Magnons) in Europe a relatively rapid succession of often complex stone artefact technologies took place during this period, including the Châtelperronian, Aurignacian, Solutrean, Gravettian and Magdalenian. The Americas were colonised via the Bering land bridge which was exposed during this period by lower sea levels. These people are called the Paleo Indians, and the earliest accepted dates are those of the Clovis culture sites, some 13,500 years ago. Globally, societies were hunter-gatherers but evidence of regional identities begins to appear in the wide variety of stone tool types being developed to suit different environments.

Epipalaeolithic/Mesolithic

Main articles: Epipalaeolithic, Mesolithic The period between the end of the last ice age, 10,000 years ago to around 6,000 years ago, is characterised by rising sea levels and a need to adapt to a changing environment and find new food sources. The development of microlith tools began in response to these changes. They were derived from the previous Palaeolithic tools, hence the term Epipalaeolithic. However, in Europe the term Mesolithic (Middle Stone Age) is used, as the tools (and way of life) was imported from the Near East. There, microlith tools permitted more efficient hunting, while more complex settlements, such as Lepenski Vir developed based around fishing. Domestication of the dog as a hunting companion probably dates to this period.

Neolithic

dog The Neolithic (New Stone Age) is characterised by the adoption of agriculture (the so-called Neolithic Revolution), the development of pottery and more complex, larger settlements such as Çatal Hüyük and Jericho. The first Neolithic cultures started around 8000 BC in the fertile crescent. Agriculture and the culture it led to spread to the Mediterranean, the Indus valley, China, and Southeast Asia. Due to the increased need to harvest and process plants, ground stone and polished stone artefacts became much more widespread, including tools for grinding, cutting, chopping and adzing. The first large-scale constructions were built, including settlement towers and walls (e.g., Jericho) and ceremonial sites (e.g., Stonehenge). These show that there was sufficient resources and co-operation to enable large groups to work on these projects. To what extent this was the development of elites and social hierarchies is a matter of on-going debate. The earliest evidence for established trade exists in the Neolithic with newly settled people importing exotic goods over distances of many hundreds of miles.

Stone Age material culture

Food and drink

Food sources of the hunter-gatherer humans of the Stone Age included both animals and plants that were part of the natural environment in which these humans lived. These humans liked animal organ meats, including the liver, kidneys, and brains. They consumed little dairy food or carbohydrate-rich plant foods like legumes or cereal grains. Current research indicates that two-thirds of the energy was derived from animal foods. The fat content of the diet was believed to be similar to that of the present day, but the ratio of the types of fats consumed differed: the Omega-6 to Omega-3 ratio was about 3:1 compared to 12:1 of today. Near the end of the last ice age, 15,000 to 9,000 years ago, a large scale extinction of large mammals (the mammalian megafauna) occurred in Asia, Europe, North America and Australia. This was the first Holocene extinction event. This event possibly forced modification in the dietary habits of the humans of that age and with the emergence of agricultural practices, plant-based foods also became a regular part of the diet. A report in the National Geographic News indicated that "the first wine-tasting may have occurred when Neolithic humans slurped the juice of naturally fermented wild grapes from animal-skin pouches or crude wooden bowls."

Shelters and habitats

Around 2 million years before present, Homo habilis is believed to have constructed first man-made structure in East Africa, consisting of simple arrangements of stones to hold branches of trees in position. Almost similar stone arrangements in circle believed to be around 500,000 years old was discovered at Terra Amata, near Nice (France). Several human habitats dating back to the Stone Age have been discovered in different parts of the earth, including:
- A tent-like structure inside a cave near the Grotte du Lazaret , Nice, France.
- A structure with roof supported with timber, discovered in Dolni Vestonice, Czechoslovakia, dates to around 23,000 BC. The walls were made of packed clay blocks and stones. Czechoslovakia]]
- Many huts made of mammoth bones were found in Eastern Europe and Siberia. The people who made these huts were specialised mammoth hunters. Examples have been found along the Dniepr river valley of Ukraine, including near Chernihiv, in Moravia (in the Czech Republic) and in southern Poland.
- An animal hide tent dated to around 15,000 to 10,000 BC (in the Magdalenian) was discovered at Plateau Parain, France.
- Megalithic tombs, multi-chambered, and dolmens, single-chambered, were graves with a huge stone slab stacked over other similarly large stone slabs. They have been discovered all across Europe, and were built in the Neolithic. Several tombs with copper and bronze tools have also been discovered, illustrating the problems of attempting to define periods based on technology.

Art

Pre-historic art can only be traced from surviving artefacts. Prehistoric music is inferred from found instruments, while parietal art can be found on rocks of any kind. The latter are petroglyphs and rock paintings. The art may or may not have had a religious function.

Petroglyphs

Petroglyphs appeared in the New Stone Age, commonly known as Neolithic period. A Petroglyph is an abstract or symbolic image recorded on stone, usually by prehistoric peoples, by means of carving, pecking or otherwise incised on natural rock surfaces. They were a dominant form or pre-writing symbols used in communication. Petroglyphs have been discovered in different parts of the world, including Asia (Bhimbetka, India), North America (Death Valley National Park), South America (Cumbe Mayo, Peru), and Europe (Finnmark, Norway).

Rock paintings

Finnmark, Norway] Rock paintings were painted on rock and were more naturalistic depictions than petroglyphs. In paleolithic times, the representation of humans in cave paintings was rare. Mostly, animals were painted: not only animals that were used as food but also animals that represented strength like the rhinoceros or large cats (as in the Chauvet Cave). Signs like dots were sometimes drawn. Rare human representations include handprints and half-human/half-animal figures. The Cave of Chauvet in the Ardèche département, France, contains the most important preserved cave paintings of the paleolithic era, painted around 31,000 BC. The Altamira cave paintings in Spain were done 14,000 to 12,000 BC and show, among others, bisons. The hall of bulls in Lascaux, Dordogne, France, is one of the best known cave paintings from about 15,000 to 10,000 BC. The meaning of the paintings remains unknown. The caves were not in an inhabited area, so they may have been used for seasonal rituals. The animals are accompanied by signs which suggest a possible magic use. Arrow-like symbols in Lascaux are sometimes interpreted as calendar or almanac use. But the evidence remains inconclusive. The most important work of the Mesolithic era were the marching Warriors, a rock painting at Cingle de la Mola, Castellón in Spain dated to about 7,000–4,000 BC. The technique used was probably spitting or blowing the pigments onto the rock. The paintings are quite naturalistic, though stylized. The figures are not three-dimensional, even though they overlap.

Stone Age rituals and beliefs

Modern studies and the in-depth analysis of finds dating from the Stone Age indicate certain rituals and beliefs of the people in those prehistoric times. It is now believed that activities of the Stone Age humans went beyond the immediate requirements of procuring food, body coverings, and shelters. Specific rites relating to death and burial were practiced, though certainly differing in style and execution between cultures. Several Stone Age-dated sites of the in different parts of the world indicate traces of dancing, dancing in files, and initiation rites.

Remnants of Stone Age living in modern times

Anthropologists have used several tribes to study and interpret what life during the Stone Age might have been like. Such tribes can be found in Papua New Guinea, Andaman and Nicobar Islands (India), Africa and South America.

The Stone Age in popular culture

As a slang term, "Stone Age" can be used to describe a modern civilization or group of people that live in relatively primitive conditions, even though its use is often a misnomer. The phrase "bomb them back into the Stone Age" implies a fierce attack that utterly destroys its target's infrastructure, forcing its survivors to revert to primitive technology in order to survive. The image of the caveman is commonly associated with the Stone Age. For example, the 2003 documentary series showing the evolution of humans through the Stone Age was called Walking with Cavemen, although only the last programme showed humans living in caves. While the idea that human beings and dinosaurs coexisted is sometimes portrayed in cartoons, films, and computer games, such as The Flintstones and One Million Years B.C., the notion of primates and dinosaurs co-existing is simply a [http://en.wiktionary.org/wiki/conceit conceit] of fiction and only seriously held by Young Earth creationism. Other depictions of the Stone Age include the best-selling Earth's Children series of books by Jean M. Auel, which are set in the Palaeolithic and are loosely based on archaeological and anthropological findings. The 1981 movie Quest for Fire by Jean-Jacques Annaud tells the story of a group of humans searching their lost fire.

Notes

# "[http://www.annecollins.com/stone-age-diet.htm Diet and Eating Habits in the Stone-Age]," annecollins.com (accessed June 11, 2005). # William Cocke, "[http://news.nationalgeographic.com/news/2004/07/0721_040721_ancientwine.html First Wine? Archaeologist Traces Drink to Stone Age]," National Geographic News, July 21, 2004 (accessed June 11, 2005). # M. Hoover, "[http://www.accd.edu/sac/vat/arthistory/arts1303/PALNEO.htm Art of the Paleolithic and Neolithic Eras]," from Art History Survey 1, San Antonio College (July 2001; accessed June 11, 2005). #"[http://www.owlnet.rice.edu/~hart205/Lectures/lecture2.htm Paleolithic, Mesolithic and Neolithic Art]" (lecture 2, Rice University, Houston, TX, September 2, 1998; accessed June 11, 2005). # Christopher L. C. E. Witcombe, "[http://witcombe.sbc.edu/willendorf/willendorfwomen.html Women in the Stone Age]," in the essay "The Venus of Willendorf" (accessed June 11, 2005). # See note 4 above. # [http://museums.ncl.ac.uk/flint/archrit.html Burial and mysticism in prehistory] (accessed June 11, 2005).

References

- The Times Atlas of Archaeology, Times Books, London, 1993 category:ISBN needed
-

External links

- [http://history-world.org/stone_age.htm The Stone Age]
- [http://www.personal.psu.edu/users/w/x/wxk116/axe/ Stone Age Handaxes]
- [http://www.personal.psu.edu/users/w/x/wxk116/habitat/ Stone Age Habitats] Category:Periods and stages in archaeology Category:Prehistory ko:석기시대 ja:石器時代 nb:Steinalderen

Prehistory

- The term prehistory (Greek words προ = before and ιστορία = history) is usually used to describe the period before written history became available. Paul Tournal originally coined the term Pré-historique in describing the finds he had made in the caves of southern France, and was used in French since the 1830s to describe the time before writing, then introduced into English by Daniel Wilson in 1851.
- The term became less meaningful in the 20th century as the boundary between history (strictly the written record) and other disciplines became less rigid and defined. Indeed today most historians rely on evidence from multiple sources and the notion of limiting historical study to a 5000 year span, out of a possible few million years of human existence, and of only those few world cultures that left written records, is no longer taken seriously. For example historians study the Celts, African civilizations and North American civilizations, even though they are by definition "prehistory".
- Prehistory can be said to date back to the beginning of the universe itself, although the term is most often used to describe periods when there was life on Earth; dinosaurs can be described as prehistoric animals and cavemen are described as prehistoric people.
- Because, by definition, there are no written records from prehistoric times, the information we know about the time period is informed by the fields of palaeontology, astronomy, biology, geology, anthropology, archaeology, indeed all the natural sciences.
- Human prehistory differs from history not only in terms of chronology but in the way it deals with the activities of archaeological cultures rather than named nations or individuals. Restricted to material remains rather than written records (and indeed only those remains that have survived), prehistory is anonymous. Because of this, the cultural terms used by prehistorians such as Neanderthal or Iron Age are modern, arbitrary labels, the precise definition of which are often subject to discussion and argument.
- The date marking the end of prehistory, that is the date when written historical records become a useful academic resource, varies from region to region. In Egypt it is generally accepted that prehistory ended around 3500 BC whereas in New Guinea the end of the prehistoric era is set much more recently, AD 1900.

Age systems

- Until the arrival of humans, a geologic time scale defines periods in prehistory. Archaeology has augmented this record and provided more precise divisions during later, human, prehistory.
- Human prehistory in the Old World is often subdivided by the three-age system. This system of classifying human prehistory creates three consecutive time periods, named for their respective predominant tool-making technologies. In the New World other naming schemes have been defined such as that listed in Archeology of the Americas.
- These very general systems of dividing up prehistory are being found to be increasingly inapplicable as archaeological discoveries suggest a much more complex view of prehistory.

External links

- The Neanderthal site at [http://www.geocities.com/patrickbringmans/veldwezelt-hezerwater.html Veldwezelt-Hezerwater], Belgium

Rock (geology)

, plutonic, metamorphic rock types of North America. ]] Rock is a naturally occurring aggregate of minerals and/or mineraloids. Rocks are classified by mineral and chemical composition; the texture of the constituent particles; and also by the processes that formed them. These indicators separate rocks into igneous, sedimentary, and metamorphic. Igneous rocks are formed from molten magma, and are divided into two main categories: Plutonic rock and Volcanic rock. Plutonic rocks result when the magma cools and crystallises slowly within the Earth's crust, while Volcanic rocks result from the magma reaching the surface either as lava or fragmental ejecta. Sedimentary rocks are formed by deposition of either detrital or organic matter, or chemical precipitates (evaporites), followed by compaction of the particulate matter and cementation. The latter can occur at or near the earth's surface, especially in the case of carbonate-rich sediments. Metamorphic rocks are formed by subjecting any rock type (including previously-formed metamorphic rock) to different temperature and pressure conditions than those in which the original rock was formed. These temperatures and pressures are always higher than those at the earth's surface, and must be sufficiently high so as to change the original minerals into other mineral types or else into other forms of the same minerals (e.g. by recrystallisation). The transformation of one rock type to another is described by the geological model called the rock cycle. The Earth's crust (including the lithosphere) and mantle are formed of rock.

External links

- [http://www.geol.lsu.edu/henry/Geology3041/2IgneousClassify/IgneousClassFlow.htm Classification of Igneous Rocks] Category:Geology Category:Rocks ja:岩石 ms:Batu th:หิน

Flint

Flint (or flintstone) is a hard, sedimentary cryptocrystalline silicate rock with a glassy appearance. Flint is usually dark-grey, blue, black, or deep brown in colour. It occurs chiefly as nodules and masses in chalks and limestones. A type of chert, this material is one of the most commonly used materials for the manufacture of stone tools during the Stone Age, as it splits into thin, sharp splinters called flakes or blades (depending in the shape) when struck by another hard object (such as a hammerstone made of another material). It remained an essential mineral resource for making fire, including the flintlocks on early firearms, until the close of the 18th century. It was also used extensively from the 13th century until the present day as a material for building stone walls, especially in England. In Europe, some of the best toolmaking flint has come from Belgium (Obourg, flint mines of Spiennes), the coastal chalks of the English Channel, the Paris Basin, the Sennonian deposits of Rügen and the Jurassic deposits of the Kraków-area in Poland. Flint mining is attested since the Palaeolithic, but became more common since the Neolithic (Michelsberg culture, Funnelbeaker culture). Funnelbeaker culture, Rügen]]

External links

- [http://www.theaaca.com/Learning_Center/flintvs.htm Flint vs Chert Authentic Artefacts Collectors Assn.]
- [http://www.science.uwaterloo.ca/earth/waton/f9811.html General quartz & silica ref.]
- [http://www.flintsource.net/ Flintsource.net European Artefacts - detailed site] Category:Sedimentary rocks Category:Lithics ko:플린트 ja:燧石

Chert

Chert is a fine-grained silica-rich cryptocrystalline sedimentary rock that may contain small fossils. It varies greatly in color from white to black, but most often manifests as gray, brown, grayish brown and light green to rusty red; its color is an expression of trace elements present in the rock, and both red and green are most often related to traces of iron (in its oxidized and reduced forms respectively). Jasper is basically chert which owes its red color to iron(III) inclusions. Chert outcrops as oval to irregular nodules in limestone, chalk, and dolostone formations as a replacement mineral, as well as in thin beds when it is a primary deposit. Thick beds of chert occur in deep geosynclinal deposits. These thickly bedded cherts include the novaculite of the Ouachita Mountains of Arkansas, Oklahoma, and similar occurrences in Texas in the United States. The banded iron formations of Precambrian age are composed of alternating layers of chert and iron oxides. Chert is generally considered to be less attractive and more common than flint, although the two materials are closely related. In geological terms flint and chert are the same, with the term flint referring to chert found in chalk.

Chert and Precambrian fossils

The cryptocrystalline nature of chert, combined with its above average ability to resist weathering, recrystallisation and metamorphism has made it an ideal rock for preservation of early life forms. For example:
- The 3.2 billion year old chert of the Fig Tree Formation in the Barbeton Mountains between Swaziland and South Africa preserved non-colonial unicellular bacterial-like fossils.
- The Gunflint Chert of western Ontario (1.9 to 2.3 BYA) preserves not only bacteria and cyanobacteria but also organisms believed to be ammonia-consuming and some that resemble green algae and fungus-like organisms.
- The Apex Chert (3.4 BYA) of the Pilbara Craton, Australia preserved eleven taxa of prokaryotes.
- The Devonian Rhynie chert (400 MYA) of Scotland has the oldest remains of land flora, and the preservation is so perfect that it allows cellular studies of the fossils.

Chert and flint: archaeological and historical uses

In prehistoric times, chert was often used as a source material for stone tools. Like flint, obsidian, and chalcedony, as well as some rhyolites, felsites, quartzites and a few other tool stones used in lithic reduction, chert fractures in a Hertzian cone when struck with sufficient force. This results in conchoidal fractures, a characteristic of all minerals with no cleavage planes. In this kind of fracture, a cone of force propagates through the material from the point of impact, eventually removing a full or partial cone; this result is familiar to anyone who has seen what happens to a plate-glass window when struck by a small object, such as an airgun projectile. The partial Hertzian cones produced during lithic reduction are called flakes, and exhibit features characteristic of this sort of breakage, including striking platforms, bulbs of force, and occasionally eraillures, which are small secondary flakes detached from the flake's bulb of force. When a chert stone is struck against steel, sparks result. This makes it an excellent tool for starting fires, and both flint and chert were used in various types of fire-starting tools, such as tinderboxes, throughout history. A primary historic use of chert was as flints for flintlock firearms, in which flint or chert striking a metal plate produces a spark that ignites a small reservoir containing black powder, discharging the firearm. In some areas chert is ubiquitous as stream gravel and fieldstone and is used as construction material and road surfacing.

References and external links

- [http://www.lpi.usra.edu/meetings/marsmet98/pdf/7033.pdf Fig Tree Formation of South Africa]
- [http://www.globalcommunity.org/wtt/walk_photos/3200.htm Photo & note re: Fig Tree Formation]
- [http://www2.bc.edu/~strother/GE_146/labs/lab7/Archaean.html Microphotographs of Fig Tree fossils]
- [http://gsc.nrcan.gc.ca/paleochron/05_e.php Gunflint chert]
- [http://www.uni-muenster.de/GeoPalaeontologie/Palaeo/Palbot/seite1.html THE EARLIEST LIFE: Annotated listing]
- [http://www.lpi.usra.edu/meetings/lpsc2003/pdf/1267.pdf BIOGENICITY OF MICROFOSSILS IN THE APEX CHERT]
- Schopf, J.W. (1999) Cradle of Life: The Discovery of Earth's Earliest Fossils, Princeton University Press, 336 p. ISBN 0691002304 Category:Petrology Category:Sedimentary rocks Category:Lithics ja:チャート (岩石)

Weapon

:The following article refers to the instrument of fighting or hunting. For other uses, see Weapon (disambiguation). See military technology and equipment for a comprehensive list of weapons and doctrines. military technology and equipment and spearpoint.]] A weapon is a tool which can be used during combat to kill or incapacitate, to destroy property, or to otherwise render resources non-functional or unavailable. It may be used to attack and defend, and consequently also to threaten. The use of weapons has been recorded since the advent of cave painting, and the process has been formulated resulting in both martial arts and strategic doctrines. Metaphorically, anything used to damage (even psychologically) can be referred to as a weapon. A weapon can be as simple as a club or as complex as an intercontinental ballistic missile (ICBM).

History

The weapon is any tool or object that is used to increase the range and power of a human hand. From the earliest traces of mankind up to our modern civilization, weapons have been a facet of human development. Weapons development has accelerated along with other areas of technology in more modern times. In ancient times, from the dawn of humanity through the Classical civilizations of Greece and Rome, weapons were primarily extensions of an individual's strength, essentially making up for the human body's lack of natural weapons such as claws. These weapons allowed the bearer to be substantially more lethal than a similar human without such a weapon. The Medieval period, including the Middle Ages, marked a period of distinct advancement in weaponry. Due to some of the unique influences of the period, weapons revolved around two major areas. First was that of knights. These horsemen required new weapons, as well as promoting development of weapons to defeat them. Second was that of castles. The building of castles on a large scale necessitated new weapons to help defend and attack them. The Renaissance marked the beginning of the implementation of combustion based devices in warfare. The most long-lasting effect of this was the introduction of cannon and firearms to the battlefield, where they are still at the core of modern weaponry. However, many other machines of war were experimented with. From the American Revolution through the beginning of the 20th Century, human-powered weapons were finally excluded from the battlefield for the most part. Sometimes referred to as the Age of Rifles, this period was characterized by the development of firearms for infantry and cannons for support, as well as the beginnings of mechanized weapons such as the machine gun. World War I marked the entry of fully industrialized warfare, and weapons as well were developed quickly to meet wartime needs. Many new technologies were developed, particularly in the development of military aircraft and vehicles. World War II however, perhaps marked the most frantic period of weapons development in the history of humanity. Massive numbers of new designs and concepts were fielded, and all existing technologies were improved between 1939 and 1945. Ultimately, the most powerful of all invented weapons was the nuclear bomb. After World War II, with the onset of the Cold War, the constant technological development of new weapons was institutionalized, as participants engaged in a constant race to develop weapons and counter-weapons. This constant state of weapons development continues into the modern era, and remains a constant draw on the resources of most nations.

Ancient Weapons

The basic tasks a weapon must perform have not changed since ancient times. All weapons do one or more of the following: #Concentrate pressure: the sharp end of a broken stone or pointed stick will apply more pressure, and do more harm, than the blunt end. A material's hardness determines its ability to apply or resist pressure. #Store energy: an object accumulates kinetic energy as a person accelerates it, and releases this energy in a much shorter time frame upon impact, thus magnifying a person's power. #Project force: a thrown rock or long stick allow a person to affect an adversary from a distance. As shown by the preceding examples, even simple items such as rocks and sticks can often serve these functions better than the human body. The usefulness of such tools made their development of paramount importance for a humanity consisting of small, thinly spread, hunter-gatherer communities. The first known traces of weapons are from the stone age with flint knives, handaxes and heads for large darts. There is no evidence for handaxes being thrown, but very good evidence for them having been used to butcher animals. Instead, darts seem to have been a powerful projectile weapon: anthropologists have thrown reconstructed darts through several inches of oak using atlatls. The broad, leaf-shaped heads penetrate deeply, and easily cut arteries. arteries Some weapons are probably much older than the dart, although little early evidence for them exists. These include the sling and the spear. Even though these weapons are quite simple, they were a major military weapon at least until Roman times; a unit of fast-moving skirmishers could be equipped with them at very little cost. Lack of early evidence is understandable, as slings are prone to decay, and it would be difficult to prove that a particular stone has been used as ammunition. Similarly, there is less incentive to put a stone point onto a spear than a dart. A weighted spear point is a liability rather than an asset, and the greater momentum imparted by stabbing makes sharpness less critical than toughness, so that points of bone, antler, or even fire-hardened wood can make more effective spear points. Once metal became available, its toughness made spears and pikes the core of most infantry forces. Some of the earliest evidence for arrows are from ca. 20,000 BC in the Levant (the so-called 'Geometric Kebaran' period), made with several very small sharp pieces of stone embedded in an arrowshaft. Here again, far earlier examples may have been subject to decay: for instance, some cultures make weighted arrow points by cutting a hollow reed diagonally and filling the end segment with clay. Archery and swords have been crucial for warfare. Archery, because of the large amount of energy that can be easily stored and released using a bow, and short swords because of their lethality in close combat. Far greater energy can be stored in a composite bow than a wooden bow of the same weight due to clever mechanical design and choice of materials, but militarily such weapons were mostly limited to use in dry climates. Traditional designs are held together by animal glue (chemically similar to gelatin); moisture would weaken the glue and damage bows of this design. The long bow makes up for less exotic materials with its larger size. In another tradeoff, short swords can be optimized for either stabbing or chopping; the former focuses on pressure, the latter on energy. The gladius hispaniensis could slip through openings in armor, and Roman doctrine held that a stab wound as shallow as one inch could be lethal. The hatchet-like Greek kopis, by contrast, seems built to dismember, but its point-heavy balance might make it clumsy against comprehensive armor. The most effective defense to traditional weapons was a fortress. The doctrines to support fortresses in the age of edged weapons may have greatly influenced medieval and noble history. Medieval siege weapons were used in countervailing doctrines, but the stave-sling and even the bow often had superior range, making them unsafe to use.

Combustion-powered weapons

Firearms are qualitatively different from earlier weapons because they store energy in a combustible propellant such as gunpowder, rather than in a weight or spring. This energy is released quite rapidly, and can be restored without much effort by the user, so that even early firearms were much more powerful than human-powered weapons. They became increasingly important and effective during the 16th century to 19th century, with progressive improvements in ignition mechanisms followed by revolutionary changes in ammunition handling and propellant. During the U.S. Civil War various technologies including the machine gun and ironclad warship emerged that would be recognizable and useful military weapons today, particularly in lower-technology conflicts. In the 19th century warship propulsion changed from sail power to fossil fuel-powered steam engines. steam engineThe age of edged weapons ended abruptly just before World War I with rifled artillery, such as howitzers which are able to destroy any masonry fortress. This single invention caused a revolution in military affairs and doctrines that continues to this day. See Technology during World War I for a detailed discussion. An important feature of industrial age warfare was technological escalation - an innovation could, and would, be rapidly matched by copying it, and often with yet another innovation to counter it. The technological escalation during World War I was profound, producing armed aircraft and tanks. This continued in the period between the end of that war and the next, with continuous improvements of all weapons by all major powers. Many modern military weapons, particularly ground-based ones, are relatively minor improvements on those of World War II. See military technology during World War II for a detailed discussion.

Nuclear Weapons

The most notable, development in weaponry since World War II has been the combination and further development of two weapons first used in it—nuclear weapons and the ballistic missile, leading to its ultimate configuration: the ICBM. The mutual possession of these by the United States and the Soviet Union ensured that either nation could inflict terrible damage on the other; so terrible, in fact, that neither nation was willing to instigate direct, all-out war with the other. The indiscriminate nature of the destruction has made nuclear-tipped missiles essentially useless for the smaller wars fought since. However computer-guided weaponry of all kinds, from smart bombs to computer-aimed tank rounds, has greatly increased weaponry's accuracy.

Information Warfare

In modern warfare, since all redoubts are traps, maneuver and coordination of forces is decisive, overshadowing particular weapons. The goal of every modern commander is therefore to "operate within the observation-decision-action cycle of the enemy." In this way, the modern commander can bring overwhelming force to bear on isolated groups of the enemy, and "tactically" overwhelm an enemy. Traditional military maneuvers tried to achieve this coordination with "fronts" made of lines of military assets. These were formerly the only way to prevent harm to friendly forces. Close-order marching and drill (a traditional military skill) was an early method to get relative superiority of coordination. Derivative methods (such as "leapfrogging units to advance a line") survived into combined arms warfare to coordinate aircraft, artillery, armor and infantry. Computers are changing this. The most extreme example so far (2003) is the use of "swarm" tactics by the U.S. military in Iraq. The U.S. had instantaneous, reliably encrypted communications, perfect navigation using GPS and computer-mediated communications to aim precision weapons. In swarm tactics, small units pass through possible enemy territory. When attacked they attempt to survive by calling down immediate overwhelming showers of precision-guided air-dropped munitions for armor, and cluster bombs for enemy troops. To consolidate such a region, nearby artillery begin bombardment, and ground units rush in on safe vectors through the bombardments, avoiding them by computer-mediated navigation aids. Thus in modern warfare, satellite navigation systems, digital radios and computers give decisive advantages to ordinary military personnel armed with weapons that are otherwise unremarkable.

Types of weapons

There are essentially three facets to classifying weapon types: who uses it, how it works, and what it targets. Who uses it essentially determines how it can be employed:
- Personal weapons are designed to be used by an individual person.
- Crew served weapons are larger than personal weapons, requiring more than one crew member to operate correctly.
- Fortification weapons are designed to be mounted in a permanent installation, or used primarily within a fortification.
- Mountain weapons are designed for use by mountain forces or those operating in difficult terrain and harsh climates.
- Vehicle weapons are designed to be mounted on any type of military vehicle.
- Railway weapons are designed to be mounted on railway cars, including armored trains.
- Aircraft weapons are designed to be carried on and used by some type of aircraft, helicopter, or other aerial vehicle.
- Naval weapons are designed to be mounted on ships and submarines.
- Space weapons are designed to be used in or launched from space. How it works refers to the construction of the weapon and how it operates:
- Archery related weapons operate by using a tensioned string to launch a projectile at some target.
- Artillery are large firearms capable of launching heavy projectiles (normally explosive) over long distances.
- Biological weapons spread biological agents, attacking humans (or livestock) by causing disease and infection.
- Chemical weapons spread chemical agents, attacking humans by poisoning and causing reactions.
- Energy weapons rely on concentrating forms of energy to attack, such as lasers, electrical shocks, and thermal or sonic attack.
- Explosive weapons use a physical explosion to create blast concussion or spread shrapnel.
- Firearms use a chemical charge to launch one or more projectiles down a rifled or smoothbore barrel.
- Incendiary weapons rely on combustible materials and an ignition mechanism to cause damage by fire.
- Non-lethal weapons are used to attack and subdue humans, but are designed to minimize the risk of killing the target.
- Magnetic weapon is one that uses magnetic fields to accelerate and propel projectiles, or to focus charged particle beams.
- Mêlée weapons operate as physical extensions of the user's body and directly impact their target.
- Missiles are rockets which are guided to their target after launch. This is also a general term for projectile weapons.
- Nuclear weapons use radioactive materials to create nuclear-fission explosions above a target ("air-burst") or at ground-level.
- Primitive weapons make no use of technological or industrial elements, instead being purely constructed of easily obtainable natural materials.
- Ranged weapons cause a projectile to leave the user and (ideally) strike a target afterwards.
- Rockets use chemical propellent to accelerate a projectile (usually with an explosive warhead) towards a target and are typically unguided once fired.
- Suicide weapons are typically explosive in nature and exploit the willingness of their operator to not survive the attack to reach their target. What it targets refers to what type of target the weapon is designed to attack:
- Anti-aircraft weapons target enemy aircraft, helicopters, missiles and any other aerial vehicles in flight.
- Anti-fortification weapons are designed to target enemy installations, including bunkers and fortifications.
- Anti-personnel weapons are designed to attack people, either individually or in numbers.
- Anti-radiation weapons target enemy sources of electronic radiation, particularly radar emitters.
- Anti-ship weapons target enemy ships and vessels on water.
- Anti-submarine weapons target enemy submarines and other underwater targets.
- Anti-tank weapons are primarily used to defeat armored targets, but may be targeted against other less well armored targets.
- Area denial weapons are designed to target territory, making it unsafe or unsuitable for enemy use or travel.
- Hunting weapons are designed particularly for use against animals for hunting purposes.
- Infantry support weapons are designed to attack various threats to infantry units, supporting the infantry's operations.

Weapons by era

- Ancient
- Medieval
- Military technology during the Napoleonic wars
- Technology during World War I
- Military technology during World War II
- Military technology of the late 20th century
- Modern weapons
- All eras

External links

- [http://www.higgins.org Higgins Armory Museum]
- [http://world.guns.ru Modern Firearms Encyclopedia] Category:Military equipment Category:Security
- ko:무기 ms:Senjata ja:武器 simple:Weapon th:อาวุธ

Sandstone

]] Sandstone is a sedimentary rock composed mainly of sand-size mineral or rock grains. Most sandstone is comprised of quartz and/or feldspar because these are the most common minerals in earth's crust. Like sand, sandstone may be any color, but the most common colors are tan, brown, yellow, red, gray, and white. Since sandstone beds often form highly visible cliffs and other topographic features, certain colors of sandstone may be strongly identified with certain regions. For instance, much of the North American West is well-known for its red sandstones. Some sandstones are resistant to weathering, yet are easy to work. This makes sandstone a common building and paving material. Because of the hardness of the individual grains, uniformity of grain size, and somewhat friable nature, sandstone is an excellent material from which to make grindstones for sharpening blades and other implements. Non-friable sandstone can be used for grindstones grinding grain. Rock formations that are primarily sandstone usually allow percolation of water and are porous enough to store large quantities, making them valuable aquifers. Fine grained aquifers, such as sandstones, are more apt to filter out pollutants from the surface than are rocks with cracks and crevices such as limestones or other rocks fractured from seismic activity.

Origins

aquifer Sandstones are clastic in origin (as opposed to organic, like chalk or coal). They are formed from the cemented grains that may be fragments of a pre-existing rock, or else just mono-minerallic crystals. The cements binding these grains together are typically calcite, clays and silica. Grain sizes in sands are in the range of 0.1mm to 2mm. (Rocks with smaller grainsizes include siltstones and shales and are typically called argillaceous sediments, as are also clays. Rocks with larger grainsizes include both breccias and conglomerates and are termed rudaceous sediments.). The principal mechanism for the formation of sandstone is by the sedimentation of grains out of a fluid, such as a river, lake or sea. The environment of deposition is crucial in determining the characteristics of the resulting sandstone, which on a finer scale include its grainsize, sorting, composition and on a larger scale include the rock geometry. Principal environments of deposition may be split between terrestrial and marine, as illustrated by the following broad groupings:
- Terrestrial environments # Rivers (levees, point bars, channel sands) # Lakes
- Marine environments # Shoreface sands # Deltas # Turbidites (submarine channels)

Types of sandstone

Turbidite Once the geological characteristics of a sandstone have been established, it can then be assigned to one of three broad groups:
- arkosic sandstones, which have a high (>25%) feldspar content.
- quartzose sandstones which have a high (>90%) quartz content. Sometimes these sandstones are termed "orthoquartzites", e.g., the Tuscarora Quartzite of the Ridge-and-valley Appalachians.
- argillaceous sandstones, such as greywacke, which have a significant clay or silt content. Dholpur beige, rajpura pink,marson copper and khatu teak are some types of sandstone. Image:USDA Mineral Sandstone 93c3955.jpg|Prepared sample of sandstone Image:Sandstone Concretion.jpg|A natural sandstone formation comprised of cemented quartz sand Image:Wall Patterns.jpg|Sandstone patterns on an chamber wall in Petra Image:Arbroath_Abbey1.jpg|Arbroath Abbey, showing distinctive sandstone colouring

Quern-stone

Quern-stones are a pair of stone tools for hand grinding a wide variety of materials. The lower, stationary, stone is called a quern, whilst the upper, mobile, stone is called a handstone.

Uses of quern-stones

Quern-stones have been used throughout the world to grind materials, the most important of which was usually grain to make flour for bread-making. They were generally replaced by millstones once mechanised forms of milling appeared, particularly the water mill and the windmill, although animals were also used to operate the millstones. However, in many non-Westernised, non-mechanised cultures they are still manufactured and used regulary and have only been replaced in many parts of the world in the last century or so. As well as grain, ethnographic evidence and Mesopotamian texts shows that a wide range of materials were processed using stone querns or mortars, including nuts, seeds, fruit, vegetables, herbs, spices, meat, bark, pigments, temper and clay (Wright 1992:87f). Moreover, one study analysing quern-stones discovered that noted that a number of querns had traces of arsenic and bismuth, unlike their source rocks, and had levels of antimony which were ten times higher than those of the rocks (Lease et al 2001:235). They concluded that this was probably due to the use of these querns in the preparation of medicines, cosmetics, dyes or even in the manufacture of alloys. There are however, more surprising recorded uses of quern-stones. For example, DeBoer (2001:223), in his review of the traditional gambling games of North American tribes, reports that one of the games involved bouncing a group of split canes off a quern. A further example is recorded in the book of Judges (9:53; NRSV): “But a certain woman threw an upper-millstone on Abimelech’s head, and crushed his skull.”

Manufacture of quern-stones

The best type of stone to manufacture quern-stones from are igneous rocks such as basalt. These have naturally rough surfaces, but grains do not detach easily, so the material being ground does not become gritty. However, such rocks are not always available, meaning that quern-stones have been manufactured from a wide variety of rocks, including sandstone, quartzite and limestone. Rutter (2003) was able to show, for the southern Levant, that basalt quern-stones were preferred to those manufactured from other rock types. Basalt quern-stones were therefore transported over long-distances, leading Rutter (2003:236) to argue that, despite their every-day, utilitarian function, they were also used as a status symbol.

Types of quern-stones

There are a variety of types of quern-stone, with the two most common being the saddle quern and the rotary quern. The saddle quern is produced by grinding the handstone using parallel motions (ie pushing and pulling the handstone), which forms a shape looking like a saddle. These are the most ancient and widely used type of quern-stone. The handstones for saddle querns are generally either roughly spherical (not unlike a rolling pin) and used with both hands, or rough hemispheres and used with one hand. As the name implies, the rotary quern used circular motions to grind the material, meaning both the quern and the handstone were generally circular. Other forms of quern-stone include hopper-rubbers and Pompeian mills, both used by the Romans.

Bibliography

- DeBoer, W. 2001 Of dice and women: gambling and exchange in Native North America, In Journal of Archaeological Method and Theory 8:215-268.
- Lease, N., Laurent, R., Blackburn, M. and Fortin, M. 2001 Caractérisation pétrologie d’artefact en basalte provenant de Tell ‘Atij et de Tell Gudeda en Syrie de Nord (3000-2500 av J-C), In Serie archéométrie 1:227-240.
- Wright, K. 1992 Ground stone assemblage variations and subsistence strategies in the Levant, 22,000 to 5,500 bp, unpublished PhD thesis, Yale University.

External links

- Rutter, G. 2003 [http://myweb.tiscali.co.uk/rutter1/basalt/index.html Basaltic-rock procurement systems of the southern Levant] - Information on basaltic artefacts, including quern-stones. Also includes PDF version of the PhD thesis. Category:Archaeological artefact types

Wood

:This article describes the material produced by trees. For other uses, see Wood (disambiguation). Wood (disambiguation)]] Wood derives from woody plants, notably trees but also shrubs. Wood from the latter is only produced in small sizes, reducing the diversity of uses. Wood is a hygroscopic, cellular and anisotropic material. Dry wood is composed of fibers of cellulose (40%–50%) and hemicellulose (20%–30%) held together by lignin (25%–30%). Wood is the xylem tissue of the plant.
Uses
xylems.]] Wood has been used by man for millennia for many purposes, being many things to many people. One of its primary uses is as fuel. It may also be used as a material, for making artworks, boats, buildings, furniture, ships, tools, weapons, etc. Wood has been an important construction material since humans began building shelters, and remains in plentiful use today. Construction wood is commonly known as timber in International English, and lumber in American English. Wood may be broken down and be made into chipboard, engineered wood, hardboard, medium-density fibreboard (MDF), oriented strand board (OSB), paper or used to make other synthetic substances.
Formation
A tree increases in diameter by the formation, between the old wood and the inner bark, of new woody layers which envelop the entire stem, living branches, and roots. Where there are clear seasons, this can happen in a discrete pattern, leading to what is known as growth rings, as can be seen on the end of a log. If these seasons are annual these growth rings are annual rings. Where there is no seasonal difference growth rings are likely to be absent. Within a growth ring it may be possible to see two more or less well-defined parts. The part nearest the centre of the tree is more open textured and almost invariably lighter in color than that near the outer portion of the ring. The inner portion is formed early in the season, when growth is comparatively rapid; it is known as early wood or spring wood. The outer portion is the late wood or summer wood, being produced in the summer. In white pines there is not much contrast in the different parts of the ring, and as a result the wood is very uniform in texture and is easy to work. In hard pines, on the other hand, the late wood is very dense and is deep-colored, presenting a very decided contrast to the soft, straw-colored early wood. In ring-porous woods each season's growth is always well defined, because the large pores of the spring abut on the denser tissue of the fall before. In the diffuse-porous woods, the demarcation between rings is not always so clear and in some cases is almost (if not entirely) invisible to the unaided eye.
Knots
Knots are portions of branches included in the wood of the stem or larger branch. Branches generally originate at or near the pith (central axis) of a stem, and the living portion will increase in size through the addition of annual woody layers which are a continuation of those of the stem. The included portion is irregularly conical in shape with the tip at the pith. The fibre direction is at right angles or oblique to the grain of the stem, thus producing local cross grain. Note that a small knot may also be the result of a dormant bud. During the development of a tree the lower limbs die, but may persist for a time--often for years. Subsequent layers of growth of the stem are no longer intimately joined with the dead limb, but are laid around it. Hence dead branches produce knots which are nothing more than pegs in a hole, and likely to drop out after the tree has been sawn. In grading lumber and structural timber, knots are classified according to their form, size, soundness, and the firmness with which they are held in place. Knots materially affect checking (cracking) and warping, ease in working, and cleavability of timber. They are defects which weaken timber and depreciate its value for structural purposes where strength is an important consideration. The weakening effect is much more serious where timber is subjected to bending and tension than where under compression. The extent to which knots affect the strength of a beam depends upon their position, size, number, direction of fibre, and condition. A knot on the upper side is compressed, while one on the lower side is subjected to tension. The knot, especially (as is often the case) if there is a season check in it, offers little resistance to this tensile stress. Small knots, however, may be so located in a beam along the neutral plane as actually to increase the strength by tending to prevent longitudinal shearing. Knots in a board or plank are least injurious when they extend through it at right angles to its broadest surface. Knots which occur near the ends of a beam do not weaken it. Sound knots which occur in the central portion one-fourth the height of the beam from either edge are not serious defects. Knots do not necessarily influence the stiffness of structural timber. Only defects of the most serious character affect the elastic limit of beams. Stiffness and elastic strength are more dependent upon the quality of the wood fibre than upon defects in the beam. The effect of knots is to reduce the difference between the fibre stress at elastic limit and the modulus of rupture of beams. The breaking strength is very susceptible to defects. Sound knots do not weaken wood when subject to compression parallel to the grain. For some purposes, e.g. wall panelling, knots are considered a plus as they add visual texture to the wood, giving it a more interesting appearance.
Heartwood and sapwood
grain (centre dark spot). The dark radial lines are small knots.]] Examination of the end of a log of many species reveals a darker-colored inner portion, called the heartwood or duramen, surrounded by a lighter-colored zone called the sapwood. In some instances this distinction in color is very marked; in others, the contrast is slight, so that it is not always easy to tell where one leaves off and the other begins. The color of fresh sapwood is always light, sometimes nearly white, but more often with a decided tinge of yellow or brown. Sapwood is comparatively new wood, comprising living cells in the growing tree. All wood in a tree is first formed as sapwood. Its principal functions are to conduct water from the roots to the leaves and to store up and give back according to the season the food prepared in the leaves. The more leaves a tree bears and the more vigorous its growth, the larger the volume of sapwood required. Hence trees making rapid growth in the open have thicker sapwood for their size than trees of the same species growing in dense forests. Sometimes trees grown in the open may become of considerable size, 30 cm or more in diameter, before any heartwood begins to form, for example, in second-growth hickory, or open-grown pines. As a tree increases in age and diameter an inner portion of the sapwood becomes inactive and finally ceases to function, as the cells die. This inert or dead portion is called heartwood. Its name derives solely from its position and not from any vital importance to the tree. This is shown by the fact that a tree can thrive with its heart completely decayed. Some species begin to form heartwood very early in life, so having only a thin layer of live sapwood, while in others the change comes slowly. Thin sapwood is characteristic of such trees as chestnut, black locust, mulberry, osage-orange, and sassafras, while in maple, ash, hickory, hackberry, beech, and pine, thick sapwood is the rule. There is no definite relation between the annual rings of growth and the amount of sapwood. Within the same species the cross-sectional area of the sapwood is very roughly proportional to the size of the crown of the tree. If the rings are narrow, more of them are required than where they are wide. As the tree gets larger, the sapwood must necessarily become thinner or increase materially in volume. Sapwood is thicker in the upper portion of the trunk of a tree than near the base, because the age and the diameter of the upper sections are less. When a tree is very young it is covered with limbs almost, if not entirely, to the ground, but as it grows older some or all of them will eventually die and be broken off. Subsequent growth of wood may completely conceal the stubs which will however remain as knots. No matter how smooth and clear a log is on the outside, it is more or less knotty near the middle. Consequently the sapwood of an old tree, and particularly of a forest-grown tree, will be freer from knots than the heartwood. Since in most uses of wood, knots are defects that weaken the timber and interfere with its ease of working and other properties, it follows that sapwood, because of its position in the tree, may have certain advantages over heartwood. It is remarkable that the inner heartwood of old trees remains as sound as it usually does, since in many cases it is hundreds of years, and in a few instances thousands of years, old. Every broken limb or root, or deep wound from fire, insects, or falling timber, may afford an entrance for decay, which, once started, may penetrate to all parts of the trunk. The larvae of many insects bore into the trees and their tunnels remain indefinitely as sources of weakness. Whatever advantages, however, that sapwood may have in this connection are due solely to its relative age and position. If a tree grows all its life in the open and the conditions of soil and site remain unchanged, it will make its most rapid growth in youth, and gradually decline. The annual rings of growth are for many years quite wide, but later they become narrower and narrower. Since each succeeding ring is laid down on the outside of the wood previously formed, it follows that unless a tree materially increases its production of wood from year to year, the rings must necessarily become thinner as the trunk gets wider. As a tree reaches maturity its crown becomes more open and the annual wood production is lessened, thereby reducing still more the width of the growth rings. In the case of forest-grown trees so much depends upon the competition of the trees in their struggle for light and nourishment that periods of rapid and slow growth may alternate. Some trees, such as southern oaks, maintain the same width of ring for hundreds of years. Upon the whole, however, as a tree gets larger in diameter the width of the growth rings decreases. There may be decided differences in the grain of heartwood and sapwood cut from a large tree, particularly one that is mature. In some trees, the wood laid on late in the life of a tree is softer, lighter, weaker, and more even-textured than that produced earlier, but in other species, the reverse applies. In a large log the sapwood, because of the time in the life of the tree when it was grown, may be inferior in hardness, strength, and toughness to equally sound heartwood from the same log.
Different woods
There is a strong relationship between the properties of wood and the properties of the particular tree that yielded it. For every trees species there is a range of density for the wood it yields. There is a rough correlation between density of a wood and its strength (mechanical properties). For example, while mahogany is a medium-dense hardwood which is excellent for fine furniture crafting, balsa is light, making it useful for model building. The densest wood may be black ironwood. Wood is commonly classified as either softwood or hardwood. The wood from conifers (e.g. pine) is called softwood, and the wood from broad-leaved trees (e.g. oak) is called hardwood. These names are a bit misleading, as hardwoods are not necessarily hard, and softwoods are not necessarily soft. The well-known balsa (a hardwood) is actually softer than any commercial softwood. Conversely, some softwoods (e.g. yew) are harder than most hardwoods.
Color
In species which show a distinct difference between heartwood and sapwood the natural color of heartwood is usually darker than that of the sapwood, and very frequently the contrast is conspicuous. This is produced by deposits in the heartwood of various materials resulting from the process of growth, increased possibly by oxidation and other chemical changes, which usually have little or no appreciable effect on the mechanical properties of the wood. Some experiments on very resinous Longleaf Pine specimens, however, indicate an increase in strength. This is due to the resin which increases the strength when dry. Such resin-saturated heartwood is called "fat lighter". Structures built of fat lighter are almost impervious to rot and termites; however they are very flammable. Stumps of old longleaf pines are often dug, split into small pieces and sold as kindling for fires. Stumps thus dug may actually remain a century or more since being cut. Spruce impregnated with crude resin and dried is also greatly increased in strength thereby. Spruce Since the late wood of a growth ring is usually darker in color than the early wood, this fact may be used in judging the density, and therefore the hardness and strength of the material. This is particularly the case with coniferous woods. In ring-porous woods the vessels of the early wood not infrequently appear on a finished surface as darker than the denser late wood, though on cross sections of heartwood the reverse is commonly true. Except in the manner just stated the color of wood is no indication of strength. Abnormal discoloration of wood often denotes a diseased condition, indicating unsoundness. The black check in western hemlock is the result of insect attacks. The reddish-brown streaks so common in hickory and certain other woods are mostly the result of injury by birds. The discoloration is merely an indication of an injury, and in all probability does not of itself affect the properties of the wood. Certain rot-producing fungi impart to wood characteristic colors which thus become symptomatic of weakness. Ordinary sap-staining is due to fungous growth, but does not necessarily produce a weakening effect.
Structure
fungi (parquet).]] In coniferous or softwood species the wood cells are mostly of one kind, tracheids, and as a result the material is much more uniform in structure than that of most hardwoods. There are no vessels ("pores") in coniferous wood such as one sees so prominently in oak and ash, for example. The structure of the hardwoods is more complex. They are more or less filled with vessels: in some cases (oak, chestnut, ash) quite large and distinct, in others (buckeye, poplar, willow) too small to be seen plainly without a small hand lens. In discussing such woods it is customary to divide them into two large classes, ring-porous and diffuse-porous. In ring-porous species, such as ash, black locust, catalpa, chestnut, elm, hickory, mulberry, and oak, the larger vessels or pores (as cross sections of vessels are called) are localized in the part of the growth ring formed in spring, thus forming a region of more or less open and porous tissue. The rest of the ring, produced in summer, is made up of smaller vessels and a much greater proportion of wood fibres. These fibres are the elements which give strength and toughness to wood, while the vessels are a source of weakness. In diffuse-porous woods the pores are scattered throughout the growth ring instead of being collected in a band or row. Examples of this kind of wood are basswood, birch, buckeye, maple, poplar, and willow. Some species, such as walnut and cherry, are on the border between the two classes, forming an intermediate group. If a heavy piece of pine is compared with a light specimen it will be seen at once that the heavier one contains a larger proportion of late wood than the other, and is therefore considerably darker. The late wood of all species is denser than that formed early in the season, hence the greater the proportion of late wood the greater the density and strength. When examined under a microscope the cells of the late wood are seen to be very thick-walled and with very small cavities, while those formed first in the season have thin walls and large cavities. The strength is in the walls, not the cavities. In choosing a piece of pine where strength or stiffness is the important consideration, the principal thing to observe is the comparative amounts of early and late wood. The width of ring is not nearly so important as the proportion of the late wood in the ring. It is not only the proportion of late wood, but also its quality, that counts. In specimens that show a very large proportion of late wood it may be noticeably more porous and weigh considerably less than the late wood in pieces that contain but little. One can judge comparative density, and therefore to some extent weight and strength, by visual inspection. cherry No satisfactory explanation can as yet be given for the real causes underlying the formation of early and late wood. Several factors may be involved. In conifers, at least, rate of growth alone does not determine the proportion of the two portions of the ring, for in some cases the wood of slow growth is very hard and heavy, while in others the opposite is true. The quality of the site where the tree grows undoubtedly affects the character of the wood formed, though it is not possible to formulate a rule governing it. In general, however, it may be said that where strength or ease of working is essential, woods of moderate to slow growth should be chosen. But in choosing a particular specimen it is not the width of ring, but the proportion and character of the late wood which should govern. In the case of the ring-porous hardwoods there seems to exist a pretty definite relation between the rate of growth of timber and its properties. This may be briefly summed up in the general statement that the more rapid the growth or the wider the rings of growth, the heavier, harder, stronger, and stiffer the wood. This, it must be remembered, applies only to ring-porous woods such as oak, ash, hickory, and others of the same group, and is, of course, subject to some exceptions and limitations. In ring-porous woods of good growth it is usually the middle portion of the ring in which the thick-walled, strength-giving fibres are most abundant. As the breadth of ring diminishes, this middle portion is reduced so that very slow growth produces comparatively light, porous wood composed of thin-walled vessels and wood parenchyma. In good oak these large vessels of the early wood occupy from 6 to 10 per cent of the volume of the log, while in inferior material they may make up 25 per cent or more. The late wood of good oak, except for radial grayish patches of small pores, is dark colored and firm, and consists of thick-walled fibres which form one-half or more of the wood. In inferior oak, such fibre areas are much reduced both in quantity and quality. Such variation is very largely the result of rate of growth. Wide-ringed wood is often called "second-growth", because the growth of the young timber in open stands after the old trees have been removed is more rapid than in trees in the forest, and in the manufacture of articles where strength is an important consideration such "second-growth" hardwood material is preferred. This is particularly the case in the choice of hickory for handles and spokes. Here not only strength, but toughness and resilience are important. The results of a series of tests on hickory by the U.S. Forest Service show that: :"The work or shock-resisting ability is greatest in wide-ringed wood that has from 5 to 14 rings per inch (rings 1.8-5 mm thick), is fairly constant from 14 to 38 rings per inch (rings 0.7-1.8 mm thick), and decreases rapidly from 38 to 47 rings per inch (rings 0.5-0.7 mm thick). The strength at maximum load is not so great with the most rapid-growing wood; it is maximum with from 14 to 20 rings per inch (rings 1.3-1.8 mm thick), and again becomes less as the wood becomes more closely ringed. The natural deduction is that wood of first-class mechanical value shows from 5 to 20 rings per inch (rings 1.3-5 mm thick) and that slower growth yields poorer stock. Thus the inspector or buyer of hickory should discriminate against timber that has more than 20 rings per inch (rings less than 1.3 mm thick). Exceptions exist, however, in the case of normal growth upon dry situations, in which the slow-growing material may be strong and tough." The effect of rate of growth on the qualities of chestnut wood is summarized by the same authority as follows: :"When the rings are wide, the transition from spring wood to summer wood is gradual, while in the narrow rings the spring wood passes into summer wood abruptly. The width of the spring wood changes but little with the width of the annual ring, so that the narrowing or broadening of the annual ring is always at the expense of the summer wood. The narrow vessels of the summer wood make it richer in wood substance than the spring wood composed of wide vessels. Therefore, rapid-growing specimens with wide rings have more wood substance than slow-growing trees with narrow rings. Since the more the wood substance the greater the weight, and the greater the weight the stronger the wood, chestnuts with wide rings must have stronger wood than chestnuts with narrow rings. This agrees with the accepted view that sprouts (which always have wide rings) yield better and stronger wood than seedling chestnuts, which grow more slowly in diameter." In diffuse-porous woods, as has been stated, the vessels or pores are scattered throughout the ring instead of collected in the early wood. The effect of rate of growth is, therefore, not the same as in the ring-porous woods, approaching more nearly the conditions in the conifers. In general it may be stated that such woods of medium growth afford stronger material than when very rapidly or very slowly grown. In many uses of wood, strength is not the main consideration. If ease of working is prized, wood should be chosen with regard to its uniformity of texture and straightness of grain, which will in most cases occur when there is little contrast between the late wood of one season's growth and the early wood of the next.
Water content
Water occurs in living wood in three conditions, namely: (1) in the cell walls, (2) in the protoplasmic contents of the cells, and (3) as free water in the cell cavities and spaces. In heartwood it occurs only in the first and last forms. Wood that is thoroughly air-dried retains from 8-16% of water in the cell walls, and none, or practically none, in the other forms. Even oven-dried wood retains a small percentage of moisture, but for all except chemical purposes, may be considered absolutely dry. The general effect of the water content upon the wood substance is to render it softer and more pliable. A similar effect of common observation is in the softening action of water on paper or cloth. Within certain limits the greater the water content the greater its softening effect. Drying produces a decided increase in the strength of wood, particularly in small specimens. An extreme example is the case of a completely dry spruce block 5 cm in section, which will sustain a permanent load four times as great as that which a green block of the same size will support. The greatest increase due to drying is in the ultimate crushing strength, and strength at elastic limit in endwise compression; these are followed by the modulus of rupt