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A gaseous layer that envelops the Earth and most other planets in the solar system. Earth, Venus, Mars, Jupiter, Saturn, Uranus, Neptune, and Titan (Saturn's largest satellite) are all known to possess substantial atmospheres that are held by the…

A scientific discipline concerned with the chemical composition of the Earth's atmosphere. Topics falling within the field include the emission, transport, and deposition of atmospheric chemical species; the rates and mechanisms of chemical…

A class of the phylum Porifera, including exclusively marine sponges with a skeleton composed of spicules of calcium carbonate to which can be added a solid basal calcitic skeleton. The sponges that constitute the phylum Porifera are assigned to…

An aquatic mammalian order comprising approximately 90 living species of whales, dolphins, and porpoises and their fossil relatives. Like all other mammals, members of the order Cetacea (cetaceans) nurse their young with milk produced by the mother,…

It has been a long-held belief that, as a result of hunting habits, early humans were partly or even primarily responsible for the decline and eventual extinction of most of the largest mammalian species that inhabited ancient Africa. These large…

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 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 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…

Trees provide substantial benefits to the environment. In addition to improving air quality, reducing stormwater runoff, serving as a wildlife habitat, and sequestering carbon by absorbing carbon dioxide, trees also cool the atmosphere through shade…

A class of the phylum Porifera, including sponges with a skeleton of one- to four-rayed siliceous spicules or of spongin fibers, or both. Four taxonomic classes comprise the phylum Porifera—Calcarea, Demospongiae, Hexactinellida, and…

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 life…

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…

A study published in the journal Atmospheric Environment (April 2019), comparing the differences in air pollution caused by automobiles powered by internal combustion (conventional) engines versus electric vehicles (EVs) powered by batteries,…

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 death and disappearance of a species. The extinction of a species usually represents an end point in a long series of population extinctions. During the extinction process, unique evolutionary history is lost at every stage, but the death of the…

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,…

Ancient fossilized members of human beings and those species directly ancestral to modern humans. Fossil humans comprise all prehistoric skeletal remains of humans that are archeologically earlier than the Neolithic (necessarily an imprecise limit,…

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…

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…

Researchers surveying ice loss from 650 glaciers across a 2000-kilometer (1240-mile) west-to-east expanse of the Himalayan Mountains reported in the journal Science Advances (June 2019) significant melting caused by global climate change over the…

Any member of the extinct mammalian subfamily Glyptodontinae, comprising giant, heavily armored relatives of armadillos. The extinct prehistoric creatures known as glyptodonts (whose name is derived from the Greek term for "grooved tooth") [Fig. 1]…

All freshwater comes from precipitation over land, which is distributed on Earth as blue and green water. Blue water—that is, surface and groundwater—is stored as freshwater in lakes, streams, ice, and snow, as well as below ground. Green water is…

An extinct order of the subclass Amphidiscophora in the class Hexactinellida. These extinct sponges are distinguished from the order Amphidiscosa (class Hexactinellida, phylum Porifera) in that the birotulates are hemidiscs with asymmetrical ends.…

A class of sponges whose skeletons are made of siliceous hexactine spicules. Members of the class Hexactinellida (phylum Porifera) are commonly called glass sponges (Fig. 1). These exclusively marine sponges are widely distributed in modern oceans.…

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 ×…

Earth’s surface temperature is warming, and the Arctic region is warming even faster. Yet winters in the mid-latitudes of Asia, Europe, and the United States have been colder than average, thanks to blasts of record-breaking frigid air caused by…

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.…