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The scientific study of climate. Climate is the expected mean and variability of the weather conditions for a particular location, season, and time of day. The climate is often described in terms of the mean values of meteorological variables such…

A suspension of minute droplets or ice crystals produced by the condensation of water vapor. This article presents an outline of cloud formation upon which to base an understanding of cloud classifications. For a more technical consideration of the…

The study of the physical and dynamical processes governing the structure and development of clouds and the release from them of snow, rain, and hail (collectively known as precipitation). Precipitation (meteorology)The factors of prime importance…

A brown to black combustible carbonaceous sedimentary rock that is mined and used primarily as a fuel. Coal originated by accumulation and subsequent physical and chemical alteration of plant material over about 300 million years, and contains at…

The internal structures and processes that are involved in the acquisition and use of knowledge, including sensation, perception, attention, learning, memory, language, thinking, and reasoning. The mental processes and behaviors that constitute…

Technology used to augment human mental capacity. In contrast, technology is widely used to augment human physical capabilities. We can move faster using cars, we can lift heavier weights using cranes, and we can even fly through the air using…

The ability to discriminate light on the basis of wavelength composition. Color vision is found in humans, in other primates, and in certain species of birds, fishes, reptiles, crustaceans, and insects. These animals have visual receptors that…

Air temperatures adjusted to represent human comfort or discomfort under prevailing conditions of temperature, humidity, radiation, and wind. Theoretical formulas attempt to compare the rate of heat loss to surroundings with rate of heat production…

Clays used as raw material in manufacturing. Commercial clays are among the most important nonmetallic mineral resources. The value of clays is related to their mineralogical and chemical composition, particularly the clay mineral constituents…

A loosely defined term used for a sedimentary mineral segregation that may range in size from inches to many feet. Concretions are usually distinguished from the sedimentary matrix enclosing them by a difference in mineralogy, color, hardness, and…

A learned response performed by a human or other animal to a signal that was previously associated with an event of consequence for that human or animal. A conditioned reflex, also known as a conditioned response, is an acquired response in which…

The state of being aware of one's own existence, of one's mental states, and of the impressions made upon one's senses. Consciousness is central to human existence, yet it has proved difficult to define and characterize. Typically, consciousness…

A protuberance of the Earth's crustal shell with an area of several million square miles and with sufficient elevation above neighboring depressions (the ocean basins) so that much of it is above sea level.The term was originally applied to the most…

The concept that the world's continents once formed part of a single mass and have since drifted into their present positions.The fundamental concept is that not only have the continents drifted, but the continents are merely parts of thicker…

The response of corals to environmental stress in which they eject the single-cell algae that live within the transparent coral tissue, making the white coral skeleton visible. Corals (Fig. 1) are animals that live in a partnership (symbiosis) with…

A syndrome characterized by a generalized decline in cognition that is severe enough to cause functional impairment in daily activities. Dementia is a term used to describe a collection of symptoms of severe cognitive decline. Individuals suffering…

A heterogeneous affective disorder involving a depressed mood and/or a loss of interest in daily activities. The most common form of affective disorder is depression (also termed clinical depression) [Fig. 1]. A major depressive episode is defined…

The study of age-related changes in behavior from birth to death. Developmental psychology is an important branch of psychological analysis that investigates the development and changes of behavior over an individual's lifetime (Fig. 1). In general,…

A crystalline form of carbon and the hardest known mineral. Diamond has been found on all continents except Antarctica, although rocks associated with it have been found there. It occurs in nature as single crystals of gem (Fig. 1) or industrial…

The third planet from the Sun and the largest of the four inner, or terrestrial, planets. The Sun is an average-sized, middle-aged star situated in the Milky Way Galaxy. So far as is known, Earth (Fig. 1) is unique in the solar system in having…

The sciences that attempt to understand the origins, evolution, and behavior of the Earth in a broad context, including its place in the solar system and the universe. Many of the advances in the earth sciences have resulted from the greatly…

A sudden movement of the Earth caused by the abrupt release of accumulated strain along a fault in the interior. The released energy passes through the Earth as seismic waves (low-frequency sound waves), which cause the shaking. Seismic waves…

Disorders characterized by abnormal eating behaviors, extreme weight-control behaviors, and dysfunctional beliefs about eating, weight, and body shape. Individuals suffering from eating disorders display abnormal eating behaviors and extreme…

A burst of electromagnetic energy. In a military context—and the subject of this article—an electromagnetic pulse (EMP) is a transient electromagnetic signal produced by a nuclear explosion in or above Earth's atmosphere (Fig. 1). Though not…

A term commonly associated with both behaviors and states of mind (known as feelings) that are not under the control of reason and disturb the flow of consciously directed behavior. Emotions influence human thinking and behavior (Fig. 1), and they…

The branch of geology that deals with the ways in which geology affects people. Examples of the effect of geology on human civilizations include (1) how fertile soils develop from rocks and how these soils can become polluted by human activities;…

The branch of ecology that studies the environmental changes that occur in ecosystems in relation to fire. Disturbance is a major environmental influence in many of Earth's ecosystems. Vital to the healthy functioning of forests, savannas,…

The discipline of Earth science that investigates the chemical composition of the Earth, other planets, and the universe as a whole, as well as the chemical processes that occur within them. Geochemistry is important because basic knowledge about…

Computer-based technologies for storing, manipulating, and analyzing geographically referenced information. Attribute information and spatial information are integrated in geographic information systems (GIS) through the notion of a data layer,…

The science of the Earth. The study of the Earth's materials and of the processes that shape them is known as physical geology. Historical geology is the record of past events. Earth Earth sciencesEnergy from two sources continually produces changes…

The study of landforms, including the description, classification, origin, development, and history of planetary surface features. Emphasis is placed on the interpretation of the erosional and depositional features of the Earth's surface. However,…

Thermal or electrical power produced from the thermal energy contained in the Earth (geothermal energy). Use of geothermal energy is based thermodynamically on the temperature difference between a mass of subsurface rock and water and a mass of…

A broad field encompassing all aspects of the study of ice. Many glaciologists focus their attention on glaciers, the largest ice masses on Earth, but glaciology also includes the study of ice that forms on rivers, lakes, and the sea; ice in the…

Significant and persistent changes in the state of Earth’s climate. Earth's past climates, or paleoclimates, have alternated between ice ages and periods warmer than today over relatively long time scales (millions to tens of millions of years)…

The rise in the surface temperature of the Earth. Global warming is one of the names given to the systematic increase of globally averaged surface temperature that has been measured since the mid-nineteenth century. There is abundant evidence that…

A sensory experience that occurs in the absence of corresponding external stimulation of the relevant sensory organ or organs. A hallucination is an apparent perception of something that is not present. It typically arises from a mental or nervous…

A mineral with the chemical composition MnWO4. Hübnerite (sometimes spelled huebnerite) is the manganese member of the wolframite solid-solution series. It commonly contains small amounts of iron. It occurs in monoclinic, short, prismatic crystals.…

The application of experimental findings in behavioral science and physiology to the design and operation of technical systems in which humans are users or operators. Human-factors engineering is a scientific discipline that attempts to integrate…

A tropical cyclone with maximum sustained winds that reach or exceed a threshold of 119 km/h (74 mi/h). In the western North Pacific Ocean such a storm is known as a typhoon and in other parts as a severe tropical cyclone. Many tropical cyclones do…

Accelerating fluxes and stores of water in the atmosphere, oceans, and land regions because of global warming. Figure 1 shows the primary hydrologic cycle compartments and fluxes. The total volume of water in the Earth system is approximately 1.36 ×…

A presumed altered state of consciousness in which the hypnotized individual is usually more susceptible to suggestion than in his or her normal state. Individuals who undergo hypnosis (also known as hypnotic suggestion) appear to be in a trancelike…

A large mass of glacial ice broken off and drifted from parent glaciers or ice shelves along polar seas. Icebergs are distinguished from polar pack ice, which is sea ice, and from frozen seawater, whose rafted or hummocked fragments may resemble…

The coding, retrieval, and combination of information in perceptual recognition, learning, remembering, thinking, problem solving, and performance of sensory-motor acts. The brain is the most complex organ of the body, composed of a network of nerve…

Learning based upon the consequences of behavior. Instrumental conditioning, also referred to as operant conditioning, is a method of learning wherein behavior is altered by the effects (either positive or negative) of the resulting consequences.…

General mental ability. Intelligence is the ability to comprehend and reason about things, as well as the skillful use of knowledge. It encompasses the integrative and adaptive functions of the brain (Fig. 1) and permits complex, unstereotyped,…

The gathering, processing, storage, and recall of information received through the senses. The mechanisms involved in learning are associated with those processes, activities, structural components, and alterations of the nervous system that produce…

The harvest of animals and plants from the ocean to provide food for people and animals. Important products in marine capture fisheries include fish (Fig. 1); mollusks such as oysters, clams, and squid; and crustaceans such as crabs and shrimps.…

The pattern of care given an offspring by its mother. Maternal behavior constitutes the various aspects of behavior displayed by the female parent in the course of raising its offspring. In most species that care for their young after birth, the…

The intentions, desires, goals, and needs that determine the behavior of humans and other animals. Motivation involves psychological factors and processes that arouse and guide goal-directed behaviors in animals, including humans. With regard to…

A combustible gas that occurs beneath the surface of the earth, often found in conjunction with petroleum deposits. Its main use is for fuel, but it is also used to make carbon black, certain chemicals, and liquefied petroleum gas. Liquefied…