Term
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Definition
| The science that examines Earth, its form and composition, and the changes that it has undergone and is undergoing. |
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Definition
| Very level area of the deep-ocean floor, usually lying at the foot of the continental rise |
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Term
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Definition
| A subdivision of the mantle situated below the lithosphere. This zone of weak material exists below a depth of about 100 kilometers and in some regions as deep as 700 kilometers. The rock within this zone is easily deformed. |
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Term
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Definition
| The concept that Earth was shaped by catastrophic events of a short-term nature |
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Definition
| That portion of the seafloor adjacent to the continents. It may include the continental shelf, continental slope, and continental rise. |
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Term
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Definition
| The gently sloping surface at the base of the continental slope. |
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Term
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Definition
| The gently sloping submerged portion of the continental margin, extending from the shoreline to the continental slope. |
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Term
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Definition
| The steep gradient that leads to the deep-ocean floor and marks the seaward edge of the continental shelf. |
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Definition
| The innermost layer of Earth based on composition. Largely an iron-nickel alloy with minor amounts of oxygen, silicon, and sulfur. |
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Term
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Definition
| That part of the continental crust that has attained stability; that is, it has not been affected by significant tectonic activity during the Phanerozoic eon. It consists of the shield and stable platform. |
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Term
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Definition
| The very thing outermost layer of Earth. |
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Term
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Definition
| The portion of seafloor that lies between the continental margin and the oceanic ridge system. This region comprises almost 30 percent of the Earth's surface. |
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Term
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Definition
| A narrow, elongated depression of the seafloor. |
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Term
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Definition
| A tentative explanation that is tested to determine validity. |
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Term
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Definition
| Rock formed from the crystallization of magma. |
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Term
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Definition
| The solid innermost layer of Earth, about 1216 km in radius. |
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Term
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Definition
| The rigid outer layer of Earth, including the crust and upper mantle. |
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Term
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Definition
| The part of the mantle extending from the core-mantle boundary to a depth of 660 km. AKA mesosphere. |
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Term
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Definition
| One of Earth's compositional layers. The solid rocky shell that extends from the base of the crust to a depth of 2900 km. |
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Term
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Definition
| Rock formed by alteration of preexisting rock deep within Earth by heat, pressure, and/or chemically active fluids. |
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Term
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Definition
| A continuous mountainous ridge on the floor of all the major ocean basins and varying in width from 500 to 5000 km. Rifts at the crests of these ridges represent divergent boundaries. |
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Term
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Definition
| A layer beneath the mantle about 2270 km thick, with liquid properties. |
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Definition
| A model that illustrates the origin of the three basic rock types and the interrelatedness of Earth materials and processes. |
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Definition
| Rock formed by the weathered products of preexisting rocks that have been transported, deposited, and lithified. |
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Term
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Definition
| A large, relatively flat expanse of ancient igneous and metamorphic rocks within the craton. |
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Term
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Definition
| That part of the craton that is mantled by relatively undeformed sedimentary rocks and underlain by a basement complex of igneous and metamorphic rocks. |
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Term
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Definition
| A group of interacting or interdependent parts that form a complex whole. |
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Definition
| A well-tested and widely accepted view explaining certain observable facts. |
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Term
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Definition
| The concept that the processes that have shaped Earth in the past are the same as those operating today. |
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Definition
| A group of rock-forming minerals, including Hornblende. They are characterized by dark color and cleavage at 60 and 120 degrees. They are common as the dark portion off otherwise light-colored igneous rocks. |
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Term
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Definition
| The smallest particle that exists as an element. |
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Term
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Definition
| A rock-forming mineral, characterized by rhombohedral cleavage. It is the primary mineral comprising limestone. |
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Term
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Definition
| A substance formed by the chemical combination of two or more elements in definite proportions and usually having properties different from those of its constituent elements. |
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Term
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Definition
| The tendency of a mineral to break along planes of weak bonding. |
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Term
| Constancy of Interfacial Angles |
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Definition
| A law stating that the angle between equivalent faces of the same mineral are always the same. |
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Term
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Definition
| A chemical bond produced by the sharing of electrons. |
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Definition
| Any natural solid with an ordered, repetitive atomic structure. Generally refers to a single mineral displaying geometrically related faces. |
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Term
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Definition
| Any natural solid with an ordered, repetitive atomic structure. |
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Term
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Definition
| Characteristic combination of intersecting faces typical of specific crystalline materials. |
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Term
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Definition
| A negatively charged subatomic particle that has a negligible mass and is found outside an atom’s nucleus. |
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Term
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Definition
| A substance that cannot be decomposed into simpler substances by ordinary chemical or physical means. |
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Term
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Definition
| A group of rock-forming minerals, including Orthoclase and Plagioclase. They are mostly light-colored, with two directions of cleavage at 90 degrees. |
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Term
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Definition
| The tendency of a mineral to break randomly, in the absence of planes of weak bonding. |
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Term
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Definition
| A mineral’s resistance to scratching and abrasion. |
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Term
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Definition
| An atom or molecule that posses an electrical charge. |
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Term
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Definition
| A chemical bond between two oppositely charged ions formed by the transfer of valence electrons from one atom to the other. |
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Definition
| Variety of the same element with a different mass number; nuclei have same number of protons but different number of neutrons. |
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Term
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Definition
| The appearance or quality of light reflected from the surface of a mineral. |
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Term
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Definition
| A chemical bond present in all metals that may be characterized as an extreme type of electron sharing in which the electrons move freely from atom to atom. |
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Term
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Definition
| A series of 10 minerals used as a standard in determining hardness. |
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Term
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Definition
| A naturally occurring, inorganic crystalline material with a unique chemical structure. |
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Term
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Definition
| A rock-forming mineral, characterized by light color and one excellent direction of cleavage, resulting in shiny thin sheets. Once used as window “glass”. |
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Term
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Definition
| A rock-forming mineral, common to basalt, and characterized by olive-green color and conchoidal fracture. The gemstone Peridot, is a variety of Olivine. |
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Term
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Definition
| A group of rock-forming minerals, including Augite. They are characterized by dark color and two directions of cleavage at 90 degrees. They are common in dark-colored igneous rocks. |
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Term
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Definition
| A common rock-forming mineral, characterized by its hardness and conchoidal fracture. It is very resistant to weathering. |
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Term
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Definition
| A consolidated mixture of minerals. |
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Term
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Definition
| Any one of numerous minerals that have the silicon-oxygen tetrahedron as their basic structure. |
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Term
| Silicon-oxygen tetrahedron |
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Definition
| A structure composed of four oxygen atoms surrounding a silicon atom that constitutes the basic building block of silicate minerals. |
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Term
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Definition
| The ratio of a substance’s weight to the weight of an equal volume of water. |
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Term
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Definition
| The color of a mineral in powdered form. |
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Term
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Definition
| Describes a mineral’s toughness or its resistance to breaking or deforming. |
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Term
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Definition
| The basic building block of crystalline solids; the smallest unit that exhibits the physical and chemical properties of the particular mineral. |
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Term
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Definition
| A fine-grained igneous rock with an intermediate composition. |
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Term
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Definition
| A texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished without the aid of a microscope. |
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Term
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Definition
| A fine-grained igneous rock of mafic composition. |
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Term
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Definition
| A large mass of igneous rock that formed when magma was emplaced at depth, crystallized, and subsequently was exposed by erosion. |
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Term
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Definition
| A concept proposed by N.L. Bowen that illustrates the relationships between magma and the minerals crystallizing from it during the formation of igneous rocks. |
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Term
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Definition
| A pattern of cracks that form during cooling of molten rock to generate columns. |
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Term
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Definition
| A term used to describe intrusive igneous masses that form parallel to the bedding of the surrounding rock. |
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Term
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Definition
| The formation and growth of a crystalline solid from a liquid or gas. |
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Term
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Definition
| During the crystallization of magma, the earlier-formed minerals are denser than the liquid portion and settle to the bottom of the magma chamber. |
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Term
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Definition
| Melting that occurs as rock ascends due to a drop in confining pressure. |
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Term
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Definition
| A tabular-shaped intrusive igneous feature that cuts through the surrounding rock. |
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Term
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Definition
| A coarse-grained igneous rock with an intermediate composition. |
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Term
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Definition
| A term used to describe plutons that cut across existing rock structures, such as bedding planes. |
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Term
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Definition
| Igneous activity that occurs at Earth’s surface. |
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Term
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Definition
| A compositional group of igneous rocks indicating the rock is composed almost entirely of light-colored silicates. |
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Term
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Definition
| An igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent volcanic eruption. |
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Term
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Definition
| A coarse-grained igneous rock of mafic composition. |
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Term
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Definition
| The gradual increase in temperature with depth in the crust. The average is 30 degrees Celsius per kilometer in the upper crust. |
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Term
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Definition
| A term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals. |
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Term
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Definition
| A coarse-grained igneous rock of felsic composition. |
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Term
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Definition
| The matrix of smaller crystals within an igneous rock that has prophyritic texture. |
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Term
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Definition
| A compositional group of igneous rocks, indicating that the rock contains at least 25 percent dark silicate minerals. The other dominant mineral is plagioclase feldspar. |
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Term
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Definition
| Igneous rock that formed below Earth’s surface. AKA plutonic. |
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Term
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Definition
| A massive igneous body intruded between preexisting strata. |
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Term
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Definition
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Term
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Definition
| A compositional group of igneous rocks indicating that the rock contains substantial dark silicate minerals and calcium-rich plagioclase feldspar. |
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Term
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Definition
| A body of molten rock found at depth, including any dissolved gases and crystals. |
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Term
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Definition
| The process of altering the composition of a magma through the mixing of material from another magma body. |
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Term
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Definition
| The process of generating more than one rock type from a single magma. |
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Term
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Definition
| The liquid portion of magma excluding the solid crystals. |
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Term
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Definition
| Volcanic glass, usually of silica-rich composition. |
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Term
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Definition
| The process by which most igneous rocks melt. Since individual minerals have different melting points, most igneous rocks melt over a temperature range of a few hundred degrees. If the liquid is squeezed out after some melting has occurred, a melt with a higher silica content results. |
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Term
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Definition
| A texture of igneous rocks in which the interlocking crystals are all larger than one centimeter in diameter. |
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Term
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Definition
| An igneous rock texture in which the crystals are roughly equal in size and large enough so the individual minerals can be identified without the aid of a microscope. |
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Term
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Definition
| A light-colored glassy vesicular rock commonly having a granitic composition |
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Term
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Definition
| An igneous rock texture resulting from the consolidation of individual rock fragments that are ejected during a violent volcanic eruption. |
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Term
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Definition
| A fine-grained igneous rock of felsic composition. |
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Term
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Definition
| A tabular igneous body that was intruded parallel to the layering of preexisting rock. |
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Term
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Definition
| A pluton similar to but smalled than a batholith |
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Term
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Definition
| The size, shape, and distribution of the particles that collectively constitute a rock. |
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Term
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Definition
| A pyroclastic igneous rock composed of tiny ash-sized fragments. |
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Term
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Definition
| A compositional group of igneous rocks containing mostly olivine and pyroxene. |
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Term
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Definition
| A term applied to Aphanitic igneous rocks that contain many small cavities called vesicles. |
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Term
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Definition
| Pertaining to the activities, structures, or rock types of a volcano. |
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Term
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Definition
| A pyroclastic igneous rock in which the ash-sized fragments have been fused (welded) together by remnant heat. |
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Term
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Definition
| An inclusion of unmelted country rock in an igneous pluton. |
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Term
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Definition
| Conspicuously large crystal embedded in a matrix of finer-grained crystals. |
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Term
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Definition
| An igneous rock texture characterized by two distinctively different crystal sizes. |
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Term
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Definition
| A type of lava flow that has a jagged, blocky surface. |
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Term
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Definition
| Lava that has a surface of angular blocks associated with material having andesitic and rhyolitic compositions. |
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Term
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Definition
| A large depression typically caused by collapse or ejection of the summit area of a volcano. |
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Term
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Definition
| A rather small volcano built primarily of ejected lava fragments that consist mostly of pea to walnut-size lapilli. |
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Term
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Definition
| A volcano composed of both lava flows and pyroclastic material. |
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Term
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Definition
| The depression at the summit of a volcano. |
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Term
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Definition
| A crack in rock along which there is a distinct separation. |
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Term
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Definition
| Flows of basaltic lava that issue from numerous cracks or fissures and commonly cover extensive areas to thicknesses of hundreds of meters |
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Term
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Definition
| A vent in a volcanic area from which fumes or gases escape. |
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Term
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Definition
| Debris flows on the slopes of volcanoes that result when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels. |
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Term
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Definition
| A bulbous mass associated with an old-age volcano, produced when thick lava is slowly squeezed from the vent. |
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Term
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Definition
| Tunnel in hardened lava that acts as a horizontal conduit for lava flowing from a volcanic vent. |
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Term
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Definition
| Incandescent volcanic debris buoyed up by hot gases that moves downslope in an avalanche fashion. |
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Term
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Definition
| A lava flow with a smooth-to-ropy surface. |
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Term
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Definition
| Basaltic lava that solidifies in an underwater environment and develops a structure that resembles a pile of pillows. |
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Term
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Definition
| A highly heated mixture, largely of ash and pumice fragments, traveling down the flanks of a volcano or along the surface of the ground. |
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Term
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Definition
| Vesicular ejecta that is the product of basaltic magma. |
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Term
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Definition
| A broad, gently sloping volcano built from fluid basaltic lavas. |
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Term
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Definition
| A volcano composed of both lava flows and pyroclastic material. |
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Term
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Definition
| Volcanic rock ejected during an eruption. (Pyroclastic material) |
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Term
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Definition
| The surface opening of a conduit or pipe. |
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Term
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Definition
| A measure of a fluid’s resistance to flow. |
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Term
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Definition
| An isolated, steep-sided, erosional remnant consisting of lava that once occupied the vent of a volcano. |
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Term
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Definition
| A mountain formed from lava and/or pyroclastics. |
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Term
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Definition
| Gaseous components of magma dissolved in the melt |
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Term
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Definition
| A fan-shaped deposit of sediment formed when a stream’s slope is abruptly reduced. |
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Term
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Definition
| A wave of sand formed by a directional water or wind current, so that the wave is tipped in the direction of the current. |
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Term
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Definition
| A measure of the degree to which a sedimentary clast’s edges and corners are rounded. |
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Term
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Definition
| A nearly flat surface separating two beds of sedimentary rock, and marking the end of one deposit and beginning of another. |
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Term
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Definition
| Parallel layers of sedimentary rock. |
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Term
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Definition
| A type of chemical sediment that forms when material dissolved in water is precipitated by water-dwelling organisms. |
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Term
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Definition
| A poorly sorted detrital sedimentary rock composed of large angular clasts |
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Term
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Definition
| A type of lithification in which precipitates from water percolate through the sediment, filling open spaces and joining particles into a solid mass. |
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Term
| Chemical sedimentary rock |
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Definition
| Sedimentary rock consisting of material that was precipitated from water by either inorganic or organic means. |
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Term
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Definition
| A chemical sedimentary rock composed of microcrystalline quartz. |
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Term
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Definition
| A sedimentary rock texture consisting of broken fragments of preexisting rock. |
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Term
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Definition
| An organic sedimentary rock composed of carbon derived from plant debris. |
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Term
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Definition
| A type of lithification in which the weight of overlying material compresses more deeply buried sediment. |
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Term
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Definition
| A sedimentary rock composed of rounded, gravel-size particles |
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Term
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Definition
| Structure in which relatively thin layers are inclined at an angle to the main bedding. |
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Term
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Definition
| A term for the texture of sedimentary rocks in which the minerals form a pattern of interlocking crystals. |
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Term
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Definition
| Deposition environment that occupies the portion of the seafloor that lies between the continental margin and the oceanic ridge system. |
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Term
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Definition
| Depositional environment associated with dunes, or hills/ridges of wind-deposited sand. |
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Term
| Detrital sedimentary rock |
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Definition
| Rocks that form from the accumulation of materials that originate and are transported as solid particles derived from both mechanical and chemical weathering. |
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Term
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Definition
| A collective term for all the chemical, physical, and biological changes that take place after sediments are deposited and during and after lithification. |
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Term
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Definition
| A chemical sedimentary rock composed of the mineral dolomite. |
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Term
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Definition
| Depositional environment associated with dunes, or hills/ridges of wind-deposited sand. |
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Term
| Environment of deposition |
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Definition
| A geographic setting where sediment accumulates under a particular set of geologic processes and environmental conditions. |
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Term
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Definition
| A sedimentary rock formed of material deposited from solution by evaporation of the water. |
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Term
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Definition
| A portion of a rock unit that possesses a distinctive set of characteristics that distinguishes it from other parts of the same unit. |
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Term
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Definition
| The remains or traces of organisms preserved from the geologic past. |
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Term
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Definition
| Depositional environments associated with glaciers and glaciation. |
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Term
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Definition
| A sediment layer characterized by a decrease in sediment size from bottom to top. |
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Term
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Definition
| A chemical sedimentary rock composed of the mineral limestone. |
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Term
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Definition
| The process, generally cementation and/or compaction, of converting sediments to solid rock. |
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Term
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Definition
| A feature in some sedimentary rocks that forms when wet mud dries out, shrinks, and cracks. |
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Term
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Definition
| A term for the texture of sedimentary rocks in which the minerals form a pattern of interlocking crystals. |
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Term
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Definition
| Sedimentary rock composed of organic carbon from the remains of plants that died and accumulated on the floor of a swamp. |
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Term
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Definition
| The reduction in the angularity of a sedimentary clast’s edges and corners, usually by abrasion experienced during transportation. |
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Term
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Definition
| A white crust on the ground produced when water evaporates and leaves its dissolved materials behind. |
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Term
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Definition
| A detrital sedimentary rock composed of sand-sized particles. |
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Term
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Definition
| A detrital sedimentary rock composed of silt and clay-sized particles. |
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Term
| Shallow marine environment |
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Definition
| System of depositional environments found between the shoreline and the continental rise. |
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Term
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Definition
| The degree of similarity in particle size in sediment or sedimentary rock. |
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Term
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Definition
| Parallel layers of sedimentary rock. |
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Term
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Definition
| A wave of sand formed by oscillation or back and forth movement of water or wind, so that sides slope equally away from the peak. |
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Term
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Definition
| System of depositional environments found between the shoreline and the continental rise. |
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Term
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Definition
| A zone or halo of contact metamorphism found in the country rock surrounding an igneous intrusion |
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Term
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Definition
| Low-grade metamorphism that occurs in the lowest layers of very thick accumulations of sedimentary strata. |
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Term
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Definition
| An equal, all-sided pressure. |
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Term
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Definition
| Changes in rock caused by the heat from a nearby magma body |
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Term
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Definition
| Forces that are unequal in different directions. |
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Term
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Definition
| A term for linear arrangement of textural features often exhibited by metamorphic rocks. |
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Term
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Definition
| A high-grade foliated metamorphic rock with a banded appearance. |
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Term
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Definition
| A texture of metamorphic rocks in which dark and light silicate minerals are separated, giving the rock a banded appearance. |
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Term
| Hydrothermal metamorphism |
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Definition
| Chemical alterations that occur as hot, ion-rich water circulates through fractures in rock. |
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Term
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Definition
| The hot, watery solution that escapes from a mass of magma during the latter stages of crystallization. |
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Term
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Definition
| Metamorphism that occurs when meteorites strike Earth’s surface. |
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Term
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Definition
| A mineral that is a good indicator of the metamorphic environment in which it formed. |
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Term
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Definition
| An unfoliated metamorphic rock composed of calcite. |
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Term
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Definition
| A group of associated minerals that are used to establish the pressures and temperatures at which rocks undergo metamorphism. |
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Term
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Definition
| The degree to which a parent rock changes during metamorphism. |
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Term
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Definition
| The changes in mineral composition and texture of a rock subjected to high temperatures and pressures within Earth. |
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Term
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Definition
| A metamorphic change in composition by the interaction with fluids around a magma body. |
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Term
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Definition
| A texture of metamorphic rocks in which there is no linear arrangement of textural features. |
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Term
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Definition
| The rock from which a metamorphic rock formed. |
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Term
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Definition
| a foliate metamorphic rock that is made up mainly of very fine-grained mica. |
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Term
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Definition
| An unfoliated metamorphic rock composed of quartz. |
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Term
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Definition
| Metamorphism associated with large-scale mountain building. |
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Term
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Definition
| The tendency of rocks to split along parallel, closely spaced surfaces. |
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Term
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Definition
| A medium to coarse grained foliated metamorphic rock in which platy minerals are visible. |
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Term
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Definition
| A type of foliation characterized by parallel arrangement of platy minerals. |
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Term
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Definition
| Metamorphism caused when high-speed projectiles (meteorites) impact Earth. |
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Term
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Definition
| A low-grade foliated metamorphic rock that is fine-grained and composed of undiscernible platy minerals. |
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Term
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Definition
| The type of foliation in which there is a parallel arrangement of fine-grained metamorphic minerals. |
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Term
| Subduction zone metamorphism |
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Definition
| High-pressure, low-temperature metamorphism that occurs where sediments are carried to great depths by a subducting plate. |
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Term
| Nonmetallic mineral resource |
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Definition
| A mineral resource that is not a fuel or processed for the metals it contains. |
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Term
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Definition
| Changes in rock caused by the heat from a nearby magma body. |
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Term
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Definition
| A mineral resource that forms or accumulates over such long time spans that it must be considered as fixed in total quantity. |
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Term
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Definition
| The splitting of atomic nuclei into smaller nuclei, causing neutrons to be emitted and heat energy to be released. |
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Term
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Definition
| A set of impermeable layers and/or geologic structures that result in the accumulation of oil and gas. |
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Term
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Definition
| Usually a useful metallic (and certain non-metallic) mineral that can be mined at a profit. |
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Term
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Definition
| A very coarse-grained igneous rock commonly found as dike associated with a large mass of plutonic rock that has smaller crystals. |
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| Deposit formed when heavy minerals are mechanically concentrated by currents, most commonly streams and waves. |
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| A resource that is virtually inexhaustible or that can be replenished over relatively short time spans. |
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| Already identified deposits from which minerals can be extracted profitably. |
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| Organic material that is renewable energy derived from trees, crops and water |
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| An impermeable layer that constitutes an oil trap by preventing mobile oil and gas from escaping at the surface. |
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| Any economic mineral deposit in which the desired mineral occurs as scattered particles in the rock but in sufficient quantity to make the deposit an ore. |
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| General term for any hydrocarbon that may be used as fuel, including coal, oil, natural gas, bitumen from tar sands, and shale oil. |
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| Compact chemical structures made of water and natural gas (usually methane) that occur in permafrost and under the ocean floor at depths greater than 1720 feet. |
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| Natural steam used for power generation. |
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| Electricity generated by falling water that is used to drive turbines. |
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| The hot, watery solution that escapes from a mass of magma during the latter stages of crystallization. |
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| All discovered and undiscovered deposits of a useful mineral that can be extracted now or at some time in the future. |
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| The porous, permeable portion of an oil trap that yields oil and gas. |
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| The concentration of minor amounts of metals that are scattered through unweathered rock into economically valuable concentrations by weathering processes. |
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| A mineral filling a fracture or fault in a host rock. |
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| Mine drainage water that has been rendered acidic by the chemical alteration of pyrite exposed by the mining process. |
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| The processes by which the internal structure of a mineral is altered by the removal and/or addition of elements. |
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| The variation in the rate and degree of weathering caused by such factors as mineral makeup, degree of jointing, and climate. |
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| A common form of chemical weathering, it is the process of dissolving into a homogeneous solution, as when an acidic solution dissolves limestone. |
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| The washing out of fine soil components from the A horizon by downward-percolating water. |
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| The incorporation and transportation of material by a mobile agent, such as water, wind, or ice. |
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e
Large dome-shaped structure, usually composed of granite, formed by sheeting. |
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| The mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices. |
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| A layer in a soil profile. |
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| Organic matter in soil produced by the decomposition of plants and animals. |
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| A chemical weathering process in which minerals are altered by chemically reacting with water and acids. |
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| Fractures in rock along which there has been no movement. |
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| The depletion of soluble materials from the upper soil by downward-percolating water. |
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| The downslope movement of rock, regolith, and soil under the direct influence of gravity. |
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| The physical disintegration of rock, resulting in smaller fragments. |
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| The removal of one or more electrons from an atom or ion. |
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| The material upon which a soil develops. |
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| The layer of rock and mineral fragments that nearly everywhere covers Earth’s land surface. |
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| salt crystallization (haloclasty) causes disintegration of rocks when saline solutions seep into cracks and joints in rock |
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| A mechanical weathering process characterized by the splitting off of slablike sheets of rock. |
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| A combination of mineral and organic matter, water, and air; that portion of the regolith that supports plant growth. |
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| A vertical section through a soil, showing its succession of horizons and the underlying parent material. |
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| A soil classification system consisting of six hierarchical categories based on observable soil characteristics. |
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| Any weathering process that tends to produce a spherical shape from an initially blocky shape. |
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| An accumulation of rock debris at the base of a cliff |
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| The disintegration and decomposition of a rock at or near the surface of Earth |
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| The steepest angle at which loose material remains stationary without sliding downslope. |
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| The slow downhill movement of soil and regolith. |
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| A flow of soil and regolith containing a large amount of water. |
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| The rapid slide of a mass of rock downslope along planes of weakness. |
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| The downslope movement of water-saturated, clay-rich sediment. |
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| A type of movement common to mass-wasting processes that refers to the freefalling of detached individual pieces of any size. |
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| A type of movement common to mass-wasting processes in which water-saturated material moves downslope as a viscous fluid. |
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| Debris flows on the slopes of volcanoes that result when unstable layers of ash and debris become saturated and flow downslope, usually following stream channels. |
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| The downslope movement of rock, regolith, and soil under the direct influence of gravity. |
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| A flow of soil and regolith containing a large amount of water. |
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| Any permanently frozen subsoil. |
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| The very rapid downslope movement of rock and debris; often aided by a layer of air trapped beneath the debris. |
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| The rapid slide of a mass of rock downslope along planes of weakness. |
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| A movement common to mass-wasting processes in which the material moving downslope remains fairly coherent and moves along a well-defined surface. |
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| The downward slipping of a mass of rock or unconsolidated material moving as a unit along a curved surface. |
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| Slow, downslope flow of water-saturated materials common to permafrost areas. |
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| An unconformity in which the older strata dip at an angle different from that of the younger beds. |
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| A time span on the geologic time scale beginning about 65.5 million years ago, following the Mesozoic era. |
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| Rock layers that were deposited or emplaced parallel to each other. |
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| Establishing the equivalence of rocks of similar age in different areas. |
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| A principle of relative dating, in which a rock or fault is younger than any rock or fault through which it cuts. |
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| A type of unconformity in which the beds above and below are parallel. |
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| A unit of the geologic time scale that is a subdivision of a period. |
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| A major division of the geologic time scale. |
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| The remains or traces of organisms preserved from the geologic past. |
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| Fossil organisms succeed one another in a definite and determinable order, and any time period can be recognized by its fossil content. |
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| The division of Earth history into blocks of time – eons, eras, periods, and epochs. |
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| The time required for one-half of the atoms of a radioactive substance to decay. |
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| Pieces of one rock unit contained within another. |
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| A fossil that is associated with a particular span of geologic time. |
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| Varieties of the same element that have different mass numbers; their nuclei contain the same number of protons but different numbers of neutrons. |
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| A principle which states that sedimentary beds originate as continuous layers that extend in all directions until they grade into a different type of sediment or thin out at the edge of a sedimentary basin. |
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| A time span on the geologic time scale between the Paleozoic and Cenozoic eras (between 238 and 65.5 million years). |
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| An unconformity in which older metamorphic or igneous rocks are overlain by younger sedimentary strata. |
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| The number of years that have passed since an event occurred. |
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| Layers of sediment that are generally deposited in a horizontal or nearly horizontal position. |
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| A time span on the geologic time scale between the Precambrian and Mesozoic eras (between 542 and 251 million years). |
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| A basic unit of the geologic time scale that is a subdivision of an era. |
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| All geologic time prior to the Phanerozoic eon. |
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| The spontaneous decay of certain unstable atomic nuclei. |
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| The radioactive isotope of carbon is produced continuously in the atmosphere and used in dating events from the very recent geologic past. Also known as carbon-14 dating. |
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Definition
| Rocks and structures are placed in their proper chronological sequence or order. |
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| In any undeformed sequence of sedimentary rocks, each bed is older than the one above and younger than the one below. |
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| A surface that represents a break in the rock record, caused by erosion and nondeposition. |
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