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A troughlike glaciated valley recognized as a narrow, deep inlet of the sea between high cliffs or steep slopes. It differs from other glaciated valleys only in the fact of submergence (Fig. 1). The floors of many fjords are elongate basins…

A physiologically interactive system within which growth, adaptation, species composition, nutrient cycling, biological productivity, and energy flows among inland aquatic microbial, plant, and animal communities are integrated with the environment.…

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,…

An ordered, internally consistent, internationally recognized sequence of time intervals, each distinct in its own history and record of life on Earth, including the assignment of absolute time in years to each geologic interval. The geologic time…

The study of the Earth’s physical properties using the principles and practices of physics. Geophysics is distinguished from geology by its use of instruments to make direct and indirect measurements of the phenomena being studied in contrast to 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 caused by increasing concentrations of greenhouse gases in the atmosphere. Although carbon dioxide (CO2) is only the fourth most abundant gas in the atmosphere, it is vitally important in maintaining…

The occurrence, circulation, distribution, and properties of any liquid water residing beneath the surface of the Earth. This article excludes any water molecules that constitute mineral species such as clays. Generally, groundwater is that fraction…

The period extending for several hundred million years from the formation of the Earth, probably around 4500 million years ago (MYA) to the first known occurrence of a preserved rock record around 4000 MYA. The length of the Hadean is comparable to…

A well stimulation technique, commonly referred to as “fracking,” that is part of a larger process of the development of unconventional oil and gas wells. During hydraulic fracturing, oil and gas operators inject a treatment fluid into an oil or gas…