Soil is a mixture of organic matter, gases and organisms that together support life. Earth's body of soil, called the pedosphere, has four important functions: as a medium for plant growth as a means of water storage and purification as a modifier of Earth's atmosphere as a habitat for organismsAll of these functions, in their turn, modify the soil; the pedosphere interfaces with the lithosphere, the hydrosphere, the atmosphere, the biosphere. The term pedolith, used to refer to the soil, translates to ground stone in the sense "fundamental stone". Soil consists of a solid phase of minerals and organic matter, as well as a porous phase that holds gases and water. Accordingly, soil scientists can envisage soils as a three-state system of solids and gases. Soil is a product of several factors: the influence of climate, relief and the soil's parent materials interacting over time, it continually undergoes development by way of numerous physical and biological processes, which include weathering with associated erosion.
Given its complexity and strong internal connectedness, soil ecologists regard soil as an ecosystem. Most soils have a dry bulk density between 1.1 and 1.6 g/cm3, while the soil particle density is much higher, in the range of 2.6 to 2.7 g/cm3. Little of the soil of planet Earth is older than the Pleistocene and none is older than the Cenozoic, although fossilized soils are preserved from as far back as the Archean. Soil science has two basic branches of study: pedology. Edaphology studies the influence of soils on living things. Pedology focuses on the formation and classification of soils in their natural environment. In engineering terms, soil is included in the broader concept of regolith, which includes other loose material that lies above the bedrock, as can be found on the Moon and on other celestial objects as well. Soil is commonly referred to as earth or dirt. Soil is a major component of the Earth's ecosystem; the world's ecosystems are impacted in far-reaching ways by the processes carried out in the soil, from ozone depletion and global warming to rainforest destruction and water pollution.
With respect to Earth's carbon cycle, soil is an important carbon reservoir, it is one of the most reactive to human disturbance and climate change. As the planet warms, it has been predicted that soils will add carbon dioxide to the atmosphere due to increased biological activity at higher temperatures, a positive feedback; this prediction has, been questioned on consideration of more recent knowledge on soil carbon turnover. Soil acts as an engineering medium, a habitat for soil organisms, a recycling system for nutrients and organic wastes, a regulator of water quality, a modifier of atmospheric composition, a medium for plant growth, making it a critically important provider of ecosystem services. Since soil has a tremendous range of available niches and habitats, it contains most of the Earth's genetic diversity. A gram of soil can contain billions of organisms, belonging to thousands of species microbial and in the main still unexplored. Soil has a mean prokaryotic density of 108 organisms per gram, whereas the ocean has no more than 107 procaryotic organisms per milliliter of seawater.
Organic carbon held in soil is returned to the atmosphere through the process of respiration carried out by heterotrophic organisms, but a substantial part is retained in the soil in the form of soil organic matter. Since plant roots need oxygen, ventilation is an important characteristic of soil; this ventilation can be accomplished via networks of interconnected soil pores, which absorb and hold rainwater making it available for uptake by plants. Since plants require a nearly continuous supply of water, but most regions receive sporadic rainfall, the water-holding capacity of soils is vital for plant survival. Soils can remove impurities, kill disease agents, degrade contaminants, this latter property being called natural attenuation. Soils maintain a net absorption of oxygen and methane and undergo a net release of carbon dioxide and nitrous oxide. Soils offer plants physical support, water, temperature moderation and protection from toxins. Soils provide available nutrients to plants and animals by converting dead organic matter into various nutrient forms.
A typical soil is about 50% solids, 50% voids of which half is occupied by water and half by gas. The percent soil mineral and organic content can be treated as a constant, while the percent soil water and gas content is considered variable whereby a rise in one is balanced by a reduction in the other; the pore space allows for the infiltration and movement of air and water, both of which are critical for life existing in soil. Compaction, a common problem with soils, reduces this space, preventing air and water from reaching plant roots and soil organisms. Given sufficient time, an undifferentiated soil will evolve a soil profile which consists of two or more layers, referred to as soil horizons, that differ in one or more properties such as in their texture, density, consistency, temperature and reactivity; the horizons differ in thickness and gene
The United States of America known as the United States or America, is a country composed of 50 states, a federal district, five major self-governing territories, various possessions. At 3.8 million square miles, the United States is the world's third or fourth largest country by total area and is smaller than the entire continent of Europe's 3.9 million square miles. With a population of over 327 million people, the U. S. is the third most populous country. The capital is Washington, D. C. and the largest city by population is New York City. Forty-eight states and the capital's federal district are contiguous in North America between Canada and Mexico; the State of Alaska is in the northwest corner of North America, bordered by Canada to the east and across the Bering Strait from Russia to the west. The State of Hawaii is an archipelago in the mid-Pacific Ocean; the U. S. territories are scattered about the Pacific Ocean and the Caribbean Sea, stretching across nine official time zones. The diverse geography and wildlife of the United States make it one of the world's 17 megadiverse countries.
Paleo-Indians migrated from Siberia to the North American mainland at least 12,000 years ago. European colonization began in the 16th century; the United States emerged from the thirteen British colonies established along the East Coast. Numerous disputes between Great Britain and the colonies following the French and Indian War led to the American Revolution, which began in 1775, the subsequent Declaration of Independence in 1776; the war ended in 1783 with the United States becoming the first country to gain independence from a European power. The current constitution was adopted in 1788, with the first ten amendments, collectively named the Bill of Rights, being ratified in 1791 to guarantee many fundamental civil liberties; the United States embarked on a vigorous expansion across North America throughout the 19th century, acquiring new territories, displacing Native American tribes, admitting new states until it spanned the continent by 1848. During the second half of the 19th century, the Civil War led to the abolition of slavery.
By the end of the century, the United States had extended into the Pacific Ocean, its economy, driven in large part by the Industrial Revolution, began to soar. The Spanish–American War and World War I confirmed the country's status as a global military power; the United States emerged from World War II as a global superpower, the first country to develop nuclear weapons, the only country to use them in warfare, a permanent member of the United Nations Security Council. Sweeping civil rights legislation, notably the Civil Rights Act of 1964, the Voting Rights Act of 1965 and the Fair Housing Act of 1968, outlawed discrimination based on race or color. During the Cold War, the United States and the Soviet Union competed in the Space Race, culminating with the 1969 U. S. Moon landing; the end of the Cold War and the collapse of the Soviet Union in 1991 left the United States as the world's sole superpower. The United States is the world's oldest surviving federation, it is a representative democracy.
The United States is a founding member of the United Nations, World Bank, International Monetary Fund, Organization of American States, other international organizations. The United States is a developed country, with the world's largest economy by nominal GDP and second-largest economy by PPP, accounting for a quarter of global GDP; the U. S. economy is post-industrial, characterized by the dominance of services and knowledge-based activities, although the manufacturing sector remains the second-largest in the world. The United States is the world's largest importer and the second largest exporter of goods, by value. Although its population is only 4.3% of the world total, the U. S. holds 31% of the total wealth in the world, the largest share of global wealth concentrated in a single country. Despite wide income and wealth disparities, the United States continues to rank high in measures of socioeconomic performance, including average wage, human development, per capita GDP, worker productivity.
The United States is the foremost military power in the world, making up a third of global military spending, is a leading political and scientific force internationally. In 1507, the German cartographer Martin Waldseemüller produced a world map on which he named the lands of the Western Hemisphere America in honor of the Italian explorer and cartographer Amerigo Vespucci; the first documentary evidence of the phrase "United States of America" is from a letter dated January 2, 1776, written by Stephen Moylan, Esq. to George Washington's aide-de-camp and Muster-Master General of the Continental Army, Lt. Col. Joseph Reed. Moylan expressed his wish to go "with full and ample powers from the United States of America to Spain" to seek assistance in the revolutionary war effort; the first known publication of the phrase "United States of America" was in an anonymous essay in The Virginia Gazette newspaper in Williamsburg, Virginia, on April 6, 1776. The second draft of the Articles of Confederation, prepared by John Dickinson and completed by June 17, 1776, at the latest, declared "The name of this Confederation shall be the'United States of America'".
The final version of the Articles sent to the states for ratification in late 1777 contains the sentence "The Stile of this Confederacy shall be'The United States of America'". In June 1776, Thomas Jefferson wrote the phrase "UNITED STATES OF AMERICA" in all capitalized letters in the headline of his "original Rough draught" of the Declaration of Independence; this draft of the document did not surface unti
Pedogenesis is the process of soil formation as regulated by the effects of place and history. Biogeochemical processes act to both destroy order within soils; these alterations lead to the development of layers, termed soil horizons, distinguished by differences in color, structure and chemistry. These features occur in patterns of soil type distribution, forming in response to differences in soil forming factors. Pedogenesis is studied as a branch of the study of soil in its natural environment. Other branches of pedology are the study of soil morphology, soil classification; the study of pedogenesis is important to understanding soil distribution patterns in current and past geologic periods. Soil develops through a series of changes; the starting point is weathering of freshly accumulated parent material. Primitive microbes feed on simple compounds released by weathering, produce acids which contribute to weathering, they leave behind organic residues. New soils increase in depth by a combination of weathering, further deposition.
An estimated 1/10 mm per year rate of soil production from weathering fits observations rates. New soils can deepen from dust deposition. Soil is able to support higher forms of plants and animals, starting with pioneer species, proceeding to more complex plant and animal communities. Soils deepen with accumulation of humus due to the activities of higher plants. Topsoils deepen through soil mixing; as soils mature, they develop layers. This development of layers is the beginning of the soil profile. Russian geologist Vasily Dokuchaev regarded as the father of pedology, determined in 1883 that soil formation occurs over time under the influence of climate, vegetation and parent material, he demonstrated this in 1898 using the soil forming equation: soil = f tr tr = relative time Clorpt is a mnemonic for American soil scientist Hans Jenny's state equation for the factors influencing soil formation: S = f S soil formation cl climate o organisms r relief p parent material t time Published in 1941, Jenny's state equation in Factors of Soil Formation differs from the Vasily Dokuchaev equation, treating time as a factor, adding topographic relief, pointedly leaving the ellipsis "open" for more factors to be added as our understanding becomes more refined.
There are two principal methods that the state equation may be solved: first in a theoretical or conceptual manner by logical deductions from certain premises, second empirically by experimentation or field observation. The empirical method is still employed today, soil formation can be defined by varying a single factor and keeping the other factors constant; this led to the development of empirical models to describe pedogenesis, such as climofunctions, topofunctions and chronofunctions. Since Hans Jenny published his formulation in 1941, it has been used by innumerable soil surveyors all over the world as a qualitative list for understanding the factors that may be important for producing the soil pattern within a region. Heat and moisture affect rates of biological chemical reactions. Seasonal patterns of heat flux, water content and water movement influence the depth and pattern of removal and accumulation of soluble and colloidal constituents in soil. Climatic extremes, such as ice and wind, can cause physical weathering, soil erosion as well as deposition and accumulation of soil parent material.
Stable, humid climates cause deep soil development. Soils are more warmth. Soils can develop faster in warmer climates; the rate of chemical weathering can nearly double for each 10 degrees Celsius increase in temperature. Climate affects which organisms are present, affecting the soil chemically and physically. Soils with similar climate histories tend to produce similar soils; each soil has a unique combination of microbial, plant and human influences acting upon it. Microorganisms are influential in the mineral transformations critical to the soil forming process. Additionally, some bacteria can fix atmospheric nitrogen and some fungi are efficient at extracting deep soil phosphorus and increasing soil carbon levels in the form of glomalin. Plants hold soil against erosion, accumulated plant material build soil humus levels. Plant root exudation supports microbial activity. Animals serve to mix soil through bioturbation; the influence of man, by association, are state factors placed within the organisms state factor.
Man can import, or extract and energy in ways that change soil formation. Accelerated soil erosion due to overgrazing, Pre-Columbian terraforming the Amazon basin resulting in Terra Preta are two examples of the effects of man's management; the organisms living in and on the soil form distinct soil types. Coniferous forests have acidic leaf litter. Mixed or deciduous forests tend to form soils classed as alfisols. Prairies have high humus accumulation, along with bioturbation can create a dark, thick A horizon characteristic of mollisols. Soi
Soil classification deals with the systematic categorization of soils based on distinguishing characteristics as well as criteria that dictate choices in use. Soil classification is a dynamic subject, from the structure of the system itself, to the definitions of classes, in the application in the field. Soil classification can be approached from the perspective of soil as a material and soil as a resource. Engineers geotechnical engineers, classify soils according to their engineering properties as they relate to use for foundation support or building material. Modern engineering classification systems are designed to allow an easy transition from field observations to basic predictions of soil engineering properties and behaviors; the most common engineering classification system for soils in North America is the Unified Soil Classification System. The USCS has three major classification groups: coarse-grained soils; the USCS further subdivides the three major soil classes for clarification.
It distinguishes sands from gravels by grain size, further classifying some as "well-graded" and the rest as "poorly-graded". Silts and clays are distinguished by the soils' Atterberg limits, separates "high-plasticity" from "low-plasticity" soils as well. Moderately organic soils are considered subdivisions of silts and clays, are distinguished from inorganic soils by changes in their plasticity properties on drying; the European soil classification system is similar, differing in coding and in adding an "intermediate-plasticity" classification for silts and clays, in minor details. Other engineering soil classification systems in the United States include the AASHTO Soil Classification System, which classifies soils and aggregates relative to their suitability for pavement construction, the Modified Burmister system, which works to the USCS, but includes more coding for various soil properties. A full geotechnical engineering soil description will include other properties of the soil including color, in-situ moisture content, in-situ strength, somewhat more detail about the material properties of the soil than is provided by the USCS code.
The USCS and additional engineering description is standardized in ASTM D 2487. For soil resources, experience has shown that a natural system approach to classification, i.e. grouping soils by their intrinsic property, behaviour, or genesis, results in classes that can be interpreted for many diverse uses. Differing concepts of pedogenesis, differences in the significance of morphological features to various land uses can affect the classification approach. Despite these differences, in a well-constructed system, classification criteria group similar concepts so that interpretations do not vary widely; this is in contrast to a technical system approach to soil classification, where soils are grouped according to their fitness for a specific use and their edaphic characteristics. Natural system approaches to soil classification, such as the French Soil Reference System are based on presumed soil genesis. Systems have developed, such as USDA soil taxonomy and the World Reference Base for Soil Resources, which use taxonomic criteria involving soil morphology and laboratory tests to inform and refine hierarchical classes.
Another approach is numerical classification called ordination, where soil individuals are grouped by multivariate statistical methods such as cluster analysis. This produces natural groupings without requiring any inference about soil genesis. In soil survey, as practiced in the United States, soil classification means criteria based on soil morphology in addition to characteristics developed during soil formation. Criteria are designed to guide choices in soil management; as indicated, this is a hierarchical system, a hybrid of both natural and objective criteria. USDA soil taxonomy provides the core criteria for differentiating soil map units; this is a substantial revision of the 1938 USDA soil taxonomy, a natural system. The USDA classification was developed by Guy Donald Smith, former director of the U. S. Department of Agriculture's soil survey investigations. Soil taxonomy based soil map units are additionally sorted into classes based on technical classification systems. Land Capability Classes, hydric soil, prime farmland are some examples.
The European Union uses the World Reference Base for Soil Resources the Update 2015 of the third edition 2014. The earlier editions of the WRB were used. According to the first edition of the WRB, the booklet "Soils of the European Union" was published by the former Institute of Environment and Sustainability. In addition to scientific soil classification systems, there are vernacular soil classification systems. Folk taxonomies have been used for millennia, while scientifically based systems are recent developments; the US Occupational Safety and Health Administration requires the classification of soils to protect workers from injury when working in excavations and trenches. OSHA uses 3 soil classifications plus one for rock, based on strength but other factors which affect the stability of cut slopes: Stable Rock: natural solid mineral matter that can be excavated with vertical sides and remain intact while exposed. Type A - cohesive, plastic soils with unconfined compressive strength greater than 1.5 ton per square foot, meeting several other
USDA soil taxonomy
USDA soil taxonomy developed by United States Department of Agriculture and the National Cooperative Soil Survey provides an elaborate classification of soil types according to several parameters and in several levels: Order, Great Group, Subgroup and Series. The classification was developed by Guy Donald Smith, former director of the U. S. Department of Agriculture's soil survey investigations. A taxonomy is an arrangement in a systematic manner, they are, from most general to specific: order, great group, subgroup and series. Soil properties that can be measured quantitatively are used in this classification system – they include: depth, temperature, structure, cation exchange capacity, base saturation, clay mineralogy, organic matter content and salt content. There are 12 soil orders in soil taxonomy; the names of the orders end with the suffix -sol. The criteria for the different soil orders include properties that reflect major differences in the genesis of soils; the orders are: Alfisol -- soils with iron.
They have horizons of clay accumulation, form where there is enough moisture and warmth for at least three months of plant growth. They constitute 10% of soils worldwide. Andisol – volcanic ash soils, they are young and fertile. They cover 1% of the world's ice-free surface. Aridisol – dry soils forming under desert conditions which have fewer than 90 consecutive days of moisture during the growing season and are nonleached, they include nearly 12% of soils on Earth. Soil formation is slow, accumulated organic matter is scarce, they may have subsurface zones of duripan. Many aridisols have well-developed Bt horizons showing clay movement from past periods of greater moisture. Entisol – formed soils that lack well-developed horizons. Found on unconsolidated river and beach sediments of sand and clay or volcanic ash, some have an A horizon on top of bedrock, they are 18% of soils worldwide. Gelisol – permafrost soils with permafrost within two metres of the surface or gelic materials and permafrost within one metre.
They constitute 9% of soils worldwide. Histosol – organic soils called bog soils, are 1% of soils worldwide. Inceptisol – young soils, they show little eluviation and illuviation. They constitute 15% of soils worldwide. Mollisol – soft, dark fertile soil formed in grasslands and some hardwood forests with thick A horizons, they are 7% of soils worldwide. Oxisol – are weathered, are rich in iron and aluminum oxides or kaolin but low in silica, they have only trace nutrients due to heavy tropical rainfall and high temperatures and low CEC of the remaining clays. They are 8% of soils worldwide. Spodosol – acid soils with organic colloid layer complexed with iron and aluminium leached from a layer above, they deciduous forests in cooler climates. They constitute 4% of soils worldwide. Ultisol – acid soils in the humid tropics and subtropics, which are depleted in calcium and potassium, they are weathered, but not as weathered as Oxisols. They make up 8% of the soil worldwide. Vertisol – inverted soils, they are clay-rich and tend to swell when wet and shrink upon drying forming deep cracks into which surface layers can fall.
They are difficult to construct roads and buildings due to their high expansion rate. They constitute 2% of soils worldwide; the percentages listed above are for land area free of ice. "Soils of Mountains", which constitute the balance, have a mixture of those listed above, or are classified as "Rugged Mountains" which have no soil. The above soil orders in sequence of increasing degree of development are Entisols, Aridisols, Alfisols, Spodosols and Oxisols. Histosols and Vertisols may appear in any of the above at any time during their development; the soil suborders within an order are differentiated on the basis of soil properties and horizons which depend on soil moisture and temperature. Forty-seven suborders are recognized in the United States; the soil great group category is a subdivision of a suborder in which the kind and sequence of soil horizons distinguish one soil from another. About 185 great groups are recognized in the United States. Horizons marked by clay, iron and hard pans and soil features such as the expansion-contraction of clays and marked quantities of various salts are used as distinguishing features.
The great group categories are divided into three kinds of soil subgroups: typic and extragrade. A typic subgroup represents the basic or'typical' concept of the great group to which the described subgroup belongs. An intergrade subgroup describes the properties that suggest how it grades towards soils of other soil great groups, suborders or orders; these properties are not developed or expressed well enough to cause the soil to be included within the great group towards which they grade, but suggest similarities. Extragrade features are aberrant properties which prevent that soil from being included in another soil classification. About 1,000 soil subgroups are defined in the United States. A soil family category is a group of soils within a subgroup and describes the physical and chemical properties which affect the response of soil to agricultural management and engineering applications; the principal characteristics used to differentiate soil families include texture, mineralogy, pH, structure, the locale's precipitation pattern, soil temper
Geology is an earth science concerned with the solid Earth, the rocks of which it is composed, the processes by which they change over time. Geology can include the study of the solid features of any terrestrial planet or natural satellite such as Mars or the Moon. Modern geology overlaps all other earth sciences, including hydrology and the atmospheric sciences, so is treated as one major aspect of integrated earth system science and planetary science. Geology describes the structure of the Earth on and beneath its surface, the processes that have shaped that structure, it provides tools to determine the relative and absolute ages of rocks found in a given location, to describe the histories of those rocks. By combining these tools, geologists are able to chronicle the geological history of the Earth as a whole, to demonstrate the age of the Earth. Geology provides the primary evidence for plate tectonics, the evolutionary history of life, the Earth's past climates. Geologists use a wide variety of methods to understand the Earth's structure and evolution, including field work, rock description, geophysical techniques, chemical analysis, physical experiments, numerical modelling.
In practical terms, geology is important for mineral and hydrocarbon exploration and exploitation, evaluating water resources, understanding of natural hazards, the remediation of environmental problems, providing insights into past climate change. Geology is a major academic discipline, it plays an important role in geotechnical engineering; the majority of geological data comes from research on solid Earth materials. These fall into one of two categories: rock and unlithified material; the majority of research in geology is associated with the study of rock, as rock provides the primary record of the majority of the geologic history of the Earth. There are three major types of rock: igneous and metamorphic; the rock cycle illustrates the relationships among them. When a rock solidifies or crystallizes from melt, it is an igneous rock; this rock can be weathered and eroded redeposited and lithified into a sedimentary rock. It can be turned into a metamorphic rock by heat and pressure that change its mineral content, resulting in a characteristic fabric.
All three types may melt again, when this happens, new magma is formed, from which an igneous rock may once more solidify. To study all three types of rock, geologists evaluate the minerals; each mineral has distinct physical properties, there are many tests to determine each of them. The specimens can be tested for: Luster: Measurement of the amount of light reflected from the surface. Luster is broken into nonmetallic. Color: Minerals are grouped by their color. Diagnostic but impurities can change a mineral’s color. Streak: Performed by scratching the sample on a porcelain plate; the color of the streak can help name the mineral. Hardness: The resistance of a mineral to scratch. Breakage pattern: A mineral can either show fracture or cleavage, the former being breakage of uneven surfaces and the latter a breakage along spaced parallel planes. Specific gravity: the weight of a specific volume of a mineral. Effervescence: Involves dripping hydrochloric acid on the mineral to test for fizzing. Magnetism: Involves using a magnet to test for magnetism.
Taste: Minerals can have a distinctive taste, like halite. Smell: Minerals can have a distinctive odor. For example, sulfur smells like rotten eggs. Geologists study unlithified materials, which come from more recent deposits; these materials are superficial deposits. This study is known as Quaternary geology, after the Quaternary period of geologic history. However, unlithified material does not only include sediments. Magmas and lavas are the original unlithified source of all igneous rocks; the active flow of molten rock is studied in volcanology, igneous petrology aims to determine the history of igneous rocks from their final crystallization to their original molten source. In the 1960s, it was discovered that the Earth's lithosphere, which includes the crust and rigid uppermost portion of the upper mantle, is separated into tectonic plates that move across the plastically deforming, upper mantle, called the asthenosphere; this theory is supported by several types of observations, including seafloor spreading and the global distribution of mountain terrain and seismicity.
There is an intimate coupling between the movement of the plates on the surface and the convection of the mantle. Thus, oceanic plates and the adjoining mantle convection currents always move in the same direction – because the oceanic lithosphere is the rigid upper thermal boundary layer of the convecting mantle; this coupling between rigid plates moving on the surface of the Earth and the convecting mantle is called plate tectonics. The development of plate tectonics has provided a physical basis for many observations of the solid Earth. Long linear regions of geologic features are explained as plate boundaries. For example: Mid-ocean ridges, high regions on the seafloor where hydrothermal vents and volcanoes exist, are seen as divergent boundaries, where two plates move apart. Arcs of volcanoes and earthquakes are theorized as convergent boundaries, where one plate subducts, or moves, under another. Transform boundaries, such as the San Andreas Fault system, resulted in widespread powerful earthquakes.
Plate tectonics has provided a mechan
Laterite is a soil and rock type rich in iron and aluminium and is considered to have formed in hot and wet tropical areas. Nearly all laterites are of rusty-red coloration, they develop by prolonged weathering of the underlying parent rock. Tropical weathering is a prolonged process of chemical weathering which produces a wide variety in the thickness, grade and ore mineralogy of the resulting soils; the majority of the land area containing laterites is between the tropics of Capricorn. Laterite has been referred to as a soil type as well as being a rock type; this and further variation in the modes of conceptualizing about laterite has led to calls for the term to be abandoned altogether. At least a few researchers specializing in regolith development have considered that hopeless confusion has evolved around the name. There is no likelihood, that the name will be abandoned. Laterite was cut into brick-like shapes and used in monument-building. After 1000 CE, construction at Angkor Wat and other southeast Asian sites changed to rectangular temple enclosures made of laterite and stone.
Since the mid-1970s, some trial sections of bituminous-surfaced, low-volume roads have used laterite in place of stone as a base course. Thick laterite layers are porous and permeable, so the layers can function as aquifers in rural areas. Locally available laterites have been used in an acid solution, followed by precipitation to remove phosphorus and heavy metals at sewage-treatment facilities. Laterites are a source of aluminium ore. In Northern Ireland they once provided a major source of aluminium ores. Laterite ores were the early major source of nickel. Francis Buchanan-Hamilton first described and named a laterite formation in southern India in 1807, he named it laterite from the Latin word which means a brick. The word laterite has been used for sesquioxide-rich soil horizons. A sesquioxide is an oxide with three atoms of two metal atoms, it has been used for any reddish soil at or near the Earth's surface. Laterite covers are thick in the stable areas of the Western Ethiopian Shield, on cratons of the South American Plate, on the Australian Shield.
In Madhya Pradesh, the laterite which caps the plateau is 30 m thick. Laterites can be either soft and broken into smaller pieces, or firm and physically resistant. Basement rocks are buried under the thick weathered layer and exposed. Lateritic soils form the uppermost part of the laterite cover. Good water holding capacity: - Because the particles are so small, the water is trapped between them. - After rain, the water moves into the soil slowly. - Palms are less to suffer from drought because the rain water is held in the soil. - However, flooding after heavy rains is more likely. - Nutrient leaching is not because the water moves down slowly. - Nutrients can be washed away from the soil surface because the water stays on top of the soil and doesn’t move inside. Large surface of soil particles: - Small clay particles have a large surface area compared to sand particles. - Nutrients stick to clay soils more strongly. - Most clay soils are quite fertile and oil palms need small amounts of fertiliser.
Heavy structure: - Because of the tiny particles, the soil sticks together easily. - Digging holes or other soil management activities are difficult and should be carried out only on dry soils. - Soil compaction happens especially when the soil is wet. Once compacted, the soil becomes hard and the oil palm roots cannot grow well. Therefore, it is important to be careful with cattle grazing and with allowing machines such as trucks and excavators into the plantation after rain. Tropical weathering is a prolonged process of chemical weathering which produces a wide variety in the thickness, grade and ore mineralogy of the resulting soils; the initial products of weathering are kaolinized rocks called saprolites. A period of active laterization extended from about the mid-Tertiary to the mid-Quaternary periods. Statistical analyses show that the transition in the mean and variance levels of 18O during the middle of the Pleistocene was abrupt, it seems this abrupt change was global and represents an increase in ice mass.
The rate of laterization would have decreased with the abrupt cooling of the earth. Weathering in tropical climates continues to this day, at a reduced rate. Laterites are formed from the leaching of parent sedimentary rocks; the mechanism of leaching involves acid dissolving the host mineral lattice, followed by hydrolysis and precipitation of insoluble oxides and sulfates of iron and silica under the high temperature conditions of a humid sub-tropical monsoon climate. An essential feature for the formation of laterite is the re