Weathering is the breaking down of rocks and minerals as well as wood and artificial materials through contact with the Earth's atmosphere and biological organisms. Weathering occurs in situ, that is, in the same place, with little or no movement, thus should not be confused with erosion, which involves the movement of rocks and minerals by agents such as water, snow, wind and gravity and being transported and deposited in other locations. Two important classifications of weathering processes exist – physical and chemical weathering. Mechanical or physical weathering involves the breakdown of rocks and soils through direct contact with atmospheric conditions, such as heat, water and pressure; the second classification, chemical weathering, involves the direct effect of atmospheric chemicals or biologically produced chemicals known as biological weathering in the breakdown of rocks and minerals. While physical weathering is accentuated in cold or dry environments, chemical reactions are most intense where the climate is wet and hot.
However, both types of weathering occur together, each tends to accelerate the other. For example, physical abrasion decreases the size of particles and therefore increases their surface area, making them more susceptible to chemical reactions; the various agents act in concert to convert primary minerals to secondary minerals and release plant nutrient elements in soluble forms. The materials left over after the rock breaks down combined with organic material creates soil; the mineral content of the soil is determined by the parent material. In addition, many of Earth's landforms and landscapes are the result of weathering processes combined with erosion and re-deposition. Physical weathering called mechanical weathering or disaggregation, is the class of processes that causes the disintegration of rocks without chemical change; the primary process in physical weathering is abrasion. However and physical weathering go hand in hand. Physical weathering can occur due to temperature, frost etc. For example, cracks exploited by physical weathering will increase the surface area exposed to chemical action, thus amplifying the rate of disintegration.
Abrasion by water and wind processes loaded with sediment can have tremendous cutting power, as is amply demonstrated by the gorges and valleys around the world. In glacial areas, huge moving ice masses embedded with soil and rock fragments grind down rocks in their path and carry away large volumes of material. Plant roots pry them apart, resulting in some disintegration. However, such biotic influences are of little importance in producing parent material when compared to the drastic physical effects of water, ice and temperature change. Thermal stress weathering, sometimes called insolation weathering, results from the expansion and contraction of rock, caused by temperature changes. For example, heating of rocks by sunlight or fires can cause expansion of their constituent minerals; as some minerals expand more than others, temperature changes set up differential stresses that cause the rock to crack apart. Because the outer surface of a rock is warmer or colder than the more protected inner portions, some rocks may weather by exfoliation – the peeling away of outer layers.
This process may be accelerated if ice forms in the surface cracks. When water freezes, it expands with a force of about 1465 Mg/m^2, disintegrating huge rock masses and dislodging mineral grains from smaller fragments. Thermal stress weathering comprises thermal shock and thermal fatigue. Thermal stress weathering is an important mechanism in deserts, where there is a large diurnal temperature range, hot in the day and cold at night; the repeated heating and cooling exerts stress on the outer layers of rocks, which can cause their outer layers to peel off in thin sheets. The process of peeling off is called exfoliation. Although temperature changes are the principal driver, moisture can enhance thermal expansion in rock. Forest fires and range fires are known to cause significant weathering of rocks and boulders exposed along the ground surface. Intense localized heat can expand a boulder; the thermal heat from wildfire can cause significant weathering of rocks and boulders, heat can expand a boulder and thermal shock can occur.
The differential expansion of a thermal gradient can be understood in terms of stress or of strain, equivalently. At some point, this stress can exceed the strength of the material. If nothing stops this crack from propagating through the material, it will result in the object's structure to fail. Frost weathering called ice wedging or cryofracturing, is the collective name for several processes where ice is present; these processes include frost frost-wedging and freeze -- thaw weathering. Severe frost shattering produces huge piles of rock fragments called scree which may be located at the foot of mountain areas or along slopes. Frost weathering is common in mountain areas where the temperature is around the freezing point of water. Certain frost-susceptible soils expand or heave upon freezing as a result of water migrating via capillary action to grow ice lenses nea
A mineral is, broadly speaking, a solid chemical compound that occurs in pure form. A rock may consist of a single mineral, or may be an aggregate of two or more different minerals, spacially segregated into distinct phases. Compounds that occur only in living beings are excluded, but some minerals are biogenic and/or are organic compounds in the sense of chemistry. Moreover, living beings synthesize inorganic minerals that occur in rocks. In geology and mineralogy, the term "mineral" is reserved for mineral species: crystalline compounds with a well-defined chemical composition and a specific crystal structure. Minerals without a definite crystalline structure, such as opal or obsidian, are more properly called mineraloids. If a chemical compound may occur with different crystal structures, each structure is considered different mineral species. Thus, for example and stishovite are two different minerals consisting of the same compound, silicon dioxide; the International Mineralogical Association is the world's premier standard body for the definition and nomenclature of mineral species.
As of November 2018, the IMA recognizes 5,413 official mineral species. Out of more than 5,500 proposed or traditional ones; the chemical composition of a named mineral species may vary somewhat by the inclusion of small amounts of impurities. Specific varieties of a species sometimes have official names of their own. For example, amethyst is a purple variety of the mineral species quartz; some mineral species can have variable proportions of two or more chemical elements that occupy equivalent positions in the mineral's structure. Sometimes a mineral with variable composition is split into separate species, more or less arbitrarily, forming a mineral group. Besides the essential chemical composition and crystal structure, the description of a mineral species includes its common physical properties such as habit, lustre, colour, tenacity, fracture, specific gravity, fluorescence, radioactivity, as well as its taste or smell and its reaction to acid. Minerals are classified by key chemical constituents.
Silicate minerals comprise 90% of the Earth's crust. Other important mineral groups include the native elements, oxides, carbonates and phosphates. One definition of a mineral encompasses the following criteria: Formed by a natural process. Stable or metastable at room temperature. In the simplest sense, this means. Classical examples of exceptions to this rule include native mercury, which crystallizes at −39 °C, water ice, solid only below 0 °C. Modern advances have included extensive study of liquid crystals, which extensively involve mineralogy. Represented by a chemical formula. Minerals are chemical compounds, as such they can be described by fixed or a variable formula. Many mineral groups and species are composed of a solid solution. For example, the olivine group is described by the variable formula 2SiO4, a solid solution of two end-member species, magnesium-rich forsterite and iron-rich fayalite, which are described by a fixed chemical formula. Mineral species themselves could have a variable composition, such as the sulfide mackinawite, 9S8, a ferrous sulfide, but has a significant nickel impurity, reflected in its formula.
Ordered atomic arrangement. This means crystalline. An ordered atomic arrangement gives rise to a variety of macroscopic physical properties, such as crystal form and cleavage. There have been several recent proposals to classify amorphous substances as minerals; the formal definition of a mineral approved by the IMA in 1995: "A mineral is an element or chemical compound, crystalline and, formed as a result of geological processes." Abiogenic. Biogenic substances are explicitly excluded by the IMA: "Biogenic substances are chemical compounds produced by biological processes without a geological component and are not regarded as minerals. However, if geological processes were involved in the genesis of the compound the product can be accepted as a mineral."The first three general characteristics are less debated than the last two. Mineral classification schemes and their definitions are evolving to match recent advances in mineral science. Recent changes have included the addition of an organic class, in both the new Dana and the Strunz classification schemes.
The organic class includes a rare group of minerals with hydrocarbons. The IMA Commission on New Minerals and Mineral Names adopted in 2009 a hierarchical scheme for the naming and classification of mineral groups and group names and established seven commissions and four working groups to review and classify minerals into an official listing of their published names. According to these new r
Archaeology, or archeology, is the study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, biofacts or ecofacts and cultural landscapes. Archaeology can be considered a branch of the humanities. In North America archaeology is a sub-field of anthropology, while in Europe it is viewed as either a discipline in its own right or a sub-field of other disciplines. Archaeologists study human prehistory and history, from the development of the first stone tools at Lomekwi in East Africa 3.3 million years ago up until recent decades. Archaeology is distinct from palaeontology, the study of fossil remains, it is important for learning about prehistoric societies, for whom there may be no written records to study. Prehistory includes over 99% of the human past, from the Paleolithic until the advent of literacy in societies across the world. Archaeology has various goals, which range from understanding culture history to reconstructing past lifeways to documenting and explaining changes in human societies through time.
The discipline involves surveying and analysis of data collected to learn more about the past. In broad scope, archaeology relies on cross-disciplinary research, it draws upon anthropology, art history, ethnology, geology, literary history, semiology, textual criticism, information sciences, statistics, paleography, paleontology and paleobotany. Archaeology developed out of antiquarianism in Europe during the 19th century, has since become a discipline practiced across the world. Archaeology has been used by nation-states to create particular visions of the past. Since its early development, various specific sub-disciplines of archaeology have developed, including maritime archaeology, feminist archaeology and archaeoastronomy, numerous different scientific techniques have been developed to aid archaeological investigation. Nonetheless, archaeologists face many problems, such as dealing with pseudoarchaeology, the looting of artifacts, a lack of public interest, opposition to the excavation of human remains.
The science of archaeology grew out of the older multi-disciplinary study known as antiquarianism. Antiquarians studied history with particular attention to ancient artifacts and manuscripts, as well as historical sites. Antiquarianism focused on the empirical evidence that existed for the understanding of the past, encapsulated in the motto of the 18th-century antiquary, Sir Richard Colt Hoare, "We speak from facts not theory". Tentative steps towards the systematization of archaeology as a science took place during the Enlightenment era in Europe in the 17th and 18th centuries. In Europe, philosophical interest in the remains of Greco-Roman civilization and the rediscovery of classical culture began in the late Middle Age. Flavio Biondo, an Italian Renaissance humanist historian, created a systematic guide to the ruins and topography of ancient Rome in the early 15th century, for which he has been called an early founder of archaeology. Antiquarians of the 16th century, including John Leland and William Camden, conducted surveys of the English countryside, drawing and interpreting the monuments that they encountered.
One of the first sites to undergo archaeological excavation was Stonehenge and other megalithic monuments in England. John Aubrey was a pioneer archaeologist who recorded numerous megalithic and other field monuments in southern England, he was ahead of his time in the analysis of his findings. He attempted to chart the chronological stylistic evolution of handwriting, medieval architecture and shield-shapes. Excavations were carried out by the Spanish military engineer Roque Joaquín de Alcubierre in the ancient towns of Pompeii and Herculaneum, both of, covered by ash during the Eruption of Mount Vesuvius in AD 79; these excavations began in 1748 in Pompeii, while in Herculaneum they began in 1738. The discovery of entire towns, complete with utensils and human shapes, as well the unearthing of frescos, had a big impact throughout Europe. However, prior to the development of modern techniques, excavations tended to be haphazard; the father of archaeological excavation was William Cunnington. He undertook excavations in Wiltshire from around 1798.
Cunnington made meticulous recordings of Neolithic and Bronze Age barrows, the terms he used to categorize and describe them are still used by archaeologists today. One of the major achievements of 19th-century archaeology was the development of stratigraphy; the idea of overlapping strata tracing back to successive periods was borrowed from the new geological and paleontological work of scholars like William Smith, James Hutton and Charles Lyell. The application of stratigraphy to archaeology first took place with the excavations of prehistorical and Bronze Age sites. In the third and fourth decades of the 19th-century, archaeologists like Jacques Boucher de Perthes and Christian Jürgensen Thomsen began to put the artifacts they had found in chronological order. A major figure in the development of archaeology into a rigorous science was the army officer and ethnologist, Augustus Pitt Rivers, who began excavations on his land in England in the 1880s, his approach was methodical by the standards of the time, he is regarded as the first scientific archaeologist.
He arranged his artifacts by type or "typologically, within types by date or "chronologically"
Porosity or void fraction is a measure of the void spaces in a material, is a fraction of the volume of voids over the total volume, between 0 and 1, or as a percentage between 0% and 100%. Speaking, some tests measure the "accessible void", the total amount of void space accessible from the surface. There are many ways to test porosity in a part, such as industrial CT scanning; the term porosity is used in multiple fields including pharmaceutics, metallurgy, manufacturing, earth sciences, soil mechanics and engineering. In gas-liquid two-phase flow, the void fraction is defined as the fraction of the flow-channel volume, occupied by the gas phase or, alternatively, as the fraction of the cross-sectional area of the channel, occupied by the gas phase. Void fraction varies from location to location in the flow channel, it fluctuates with time and its value is time averaged. In separated flow, it is related to volumetric flow rates of the gas and the liquid phase, to the ratio of the velocity of the two phases.
Used in geology, soil science, building science, the porosity of a porous medium describes the fraction of void space in the material, where the void may contain, for example, air or water. It is defined by the ratio: ϕ = V V V T where VV is the volume of void-space and VT is the total or bulk volume of material, including the solid and void components. Both the mathematical symbols ϕ and n are used to denote porosity. Porosity is a fraction between 0 and 1 ranging from less than 0.01 for solid granite to more than 0.5 for peat and clay. The porosity of a rock, or sedimentary layer, is an important consideration when attempting to evaluate the potential volume of water or hydrocarbons it may contain. Sedimentary porosity is a complicated function of many factors, including but not limited to: rate of burial, depth of burial, the nature of the connate fluids, the nature of overlying sediments. One used relationship between porosity and depth is given by the Athy equation: ϕ = ϕ 0 e − k z where ϕ 0 is the surface porosity, k is the compaction coefficient and z is depth.
A value for porosity can alternatively be calculated from the bulk density ρ bulk, saturating fluid density ρ fluid and particle density ρ particle: ϕ = ρ particle − ρ bulk ρ particle − ρ fluid If the void space is filled with air, the following simpler form may be used: ϕ = 1 − ρ bulk ρ particle Normal particle density is assumed to be 2.65 g/cm3, although a better estimation can be obtained by examining the lithology of the particles. Porosity can be proportional to hydraulic conductivity; the principal complication is that there is not a direct proportionality between porosity and hydraulic conductivity but rather an inferred proportionality. There is a clear proportionality between hydraulic conductivity. There tends to be a proportionality between pore throat radii and pore volume. If the proportionality between pore throat radii and porosity exists a proportionality between porosity and hydraulic conductivity may exist. However, as grain size or sorting decreases the proportionality between pore throat radii and porosity begins to fail and therefore so does the proportionality between porosity and hydraulic conductivity.
For example: clays have low hydraulic conductivity but have high porosities, which means clays can hold a large volume of water per volume of bulk material, but they do not release water and therefore have low hydraulic conductivity. Well sorted materials have higher porosity than sized poorly sorted materials; the graphic illustrates how some smaller grains can fill the pores, drastically reducing porosity and hydraulic conductivity, while only being a small fraction of the total volume of the material. For tables of common porosity values for earth materials, see the "further reading" section in the Hydrogeology article. Consolidated roc
Collagen is the main structural protein in the extracellular space in the various connective tissues in the body. As the main component of connective tissue, it is the most abundant protein in mammals, making 25% to 35% of the whole-body protein content. Collagen consists of amino acids wound together to form triple-helices of elongated fibrils, it is found in fibrous tissues such as tendons and skin. Depending upon the degree of mineralization, collagen tissues may be rigid, compliant, or have a gradient from rigid to compliant, it is abundant in corneas, blood vessels, the gut, intervertebral discs, the dentin in teeth. In muscle tissue, it serves as a major component of the endomysium. Collagen constitutes one to two percent of muscle tissue and accounts for 6% of the weight of strong, muscles; the fibroblast is the most common cell. Gelatin, used in food and industry, is collagen that has been, hydrolyzed. Collagen has many medical uses in treating complications of skin; the name collagen comes from the Greek κόλλα, meaning "glue", suffix -γέν, -gen, denoting "producing".
This refers to the compound's early use in the process of boiling the skin and tendons of horses and other animals to obtain glue. Over 90% of the collagen in the human body is type I. However, as of 2011, 28 types of collagen have been identified and divided into several groups according to the structure they form: Fibrillar Non-fibrillar FACIT Short chain Basement membrane Multiplexin MACIT Other The five most common types are: Type I: skin, vasculature, bone Type II: cartilage Type III: reticulate found alongside type I Type IV: forms basal lamina, the epithelium-secreted layer of the basement membrane Type V: cell surfaces and placenta The collagenous cardiac skeleton which includes the four heart valve rings, is histologically and uniquely bound to cardiac muscle; the cardiac skeleton includes the separating septa of the heart chambers – the interventricular septum and the atrioventricular septum. Collagen contribution to the measure of cardiac performance summarily represents a continuous torsional force opposed to the fluid mechanics of blood pressure emitted from the heart.
The collagenous structure that divides the upper chambers of the heart from the lower chambers is an impermeable membrane that excludes both blood and electrical impulses through typical physiological means. With support from collagen, atrial fibrillation never deteriorates to ventricular fibrillation. Collagen is layered in variable densities with cardiac muscle mass; the mass, distribution and density of collagen all contribute to the compliance required to move blood back and forth. Individual cardiac valvular leaflets are folded into shape by specialized collagen under variable pressure. Gradual calcium deposition within collagen occurs as a natural function of aging. Calcified points within collagen matrices show contrast in a moving display of blood and muscle, enabling methods of cardiac imaging technology to arrive at ratios stating blood in and blood out. Pathology of the collagen underpinning of the heart is understood within the category of connective tissue disease. Collagen has been used in cosmetic surgery, as a healing aid for burn patients for reconstruction of bone and a wide variety of dental and surgical purposes.
Both human and bovine collagen is used as dermal fillers for treatment of wrinkles and skin aging. Some points of interest are: When used cosmetically, there is a chance of allergic reactions causing prolonged redness. Most medical collagen is derived from young beef cattle from certified BSE-free animals. Most manufacturers use donor animals from either "closed herds", or from countries which have never had a reported case of BSE such as Australia and New Zealand; as the skeleton forms the structure of the body, it is vital that it maintains its strength after breaks and injuries. Collagen is used in bone grafting as it has a triple helical structure, making it a strong molecule, it is ideal for use in bones. The triple helical structure of collagen prevents it from being broken down by enzymes, it enables adhesiveness of cells and it is important for the proper assembly of the extracellular matrix. Collagen scaffolds are used in tissue regeneration, whether in thin sheets, or gels. Collagen has the correct properties for tissue regeneration such as pore structure, permeability and being stable in vivo.
Collagen scaffolds are ideal for the deposition of cells such as osteoblasts and fibroblasts, once inserted, growth is able to continue as normal in the tissue. Collagens are employed in the construction of the artificial skin substitutes used in the management of severe burns and wounds; these collagens may be derived from bovine, porcine, or human sources. Collagen is one of the body’s key natural resources and a component of skin tissu
A carbohydrate is a biomolecule consisting of carbon and oxygen atoms with a hydrogen–oxygen atom ratio of 2:1 and thus with the empirical formula Cmn. This formula holds true for monosaccharides; some exceptions exist. The carbohydrates are technically hydrates of carbon; the term is most common in biochemistry, where it is a synonym of saccharide, a group that includes sugars and cellulose. The saccharides are divided into four chemical groups: monosaccharides, disaccharides and polysaccharides. Monosaccharides and disaccharides, the smallest carbohydrates, are referred to as sugars; the word saccharide comes from the Greek word σάκχαρον, meaning "sugar". While the scientific nomenclature of carbohydrates is complex, the names of the monosaccharides and disaccharides often end in the suffix -ose, as in the monosaccharides fructose and glucose and the disaccharides sucrose and lactose. Carbohydrates perform numerous roles in living organisms. Polysaccharides serve as structural components; the 5-carbon monosaccharide ribose is an important component of coenzymes and the backbone of the genetic molecule known as RNA.
The related deoxyribose is a component of DNA. Saccharides and their derivatives include many other important biomolecules that play key roles in the immune system, preventing pathogenesis, blood clotting, development, they are found in a wide variety of processed foods. Starch is a polysaccharide, it is abundant in cereals and processed food based on cereal flour, such as bread, pizza or pasta. Sugars appear in human diet as table sugar, lactose and fructose, both of which occur in honey, many fruits, some vegetables. Table sugar, milk, or honey are added to drinks and many prepared foods such as jam and cakes. Cellulose, a polysaccharide found in the cell walls of all plants, is one of the main components of insoluble dietary fiber. Although it is not digestible, insoluble dietary fiber helps to maintain a healthy digestive system by easing defecation. Other polysaccharides contained in dietary fiber include resistant starch and inulin, which feed some bacteria in the microbiota of the large intestine, are metabolized by these bacteria to yield short-chain fatty acids.
In scientific literature, the term "carbohydrate" has many synonyms, like "sugar", "saccharide", "ose", "glucide", "hydrate of carbon" or "polyhydroxy compounds with aldehyde or ketone". Some of these terms, specially "carbohydrate" and "sugar", are used with other meanings. In food science and in many informal contexts, the term "carbohydrate" means any food, rich in the complex carbohydrate starch or simple carbohydrates, such as sugar. In lists of nutritional information, such as the USDA National Nutrient Database, the term "carbohydrate" is used for everything other than water, fat and ethanol; this includes chemical compounds such as acetic or lactic acid, which are not considered carbohydrates. It includes dietary fiber, a carbohydrate but which does not contribute much in the way of food energy though it is included in the calculation of total food energy just as though it were a sugar. In the strict sense, "sugar" is applied for sweet, soluble carbohydrates, many of which are used in food.
The name "carbohydrate" was used in chemistry for any compound with the formula Cm n. Following this definition, some chemists considered formaldehyde to be the simplest carbohydrate, while others claimed that title for glycolaldehyde. Today, the term is understood in the biochemistry sense, which excludes compounds with only one or two carbons and includes many biological carbohydrates which deviate from this formula. For example, while the above representative formulas would seem to capture the known carbohydrates and abundant carbohydrates deviate from this. For example, carbohydrates display chemical groups such as: N-acetyl, carboxylic acid and deoxy modifications. Natural saccharides are built of simple carbohydrates called monosaccharides with general formula n where n is three or more. A typical monosaccharide has the structure H–x–y–H, that is, an aldehyde or ketone with many hydroxyl groups added one on each carbon atom, not part of the aldehyde or ketone functional group. Examples of monosaccharides are glucose and glyceraldehydes.
However, some biological substances called "monosaccharides" do not conform to this formula and there are many chemicals that do conform to this formula but are not considered to be monosaccharides. The open-chain form of a monosaccharide coexists with a closed ring form where the aldehyde/ketone carbonyl group carbon and hydroxyl group react forming a hemiacetal with a new C–O–C bridge. Monosaccharides can be linked togeth