Geology
The science that examines Earth, its form and composition, and the changes it has undergone and is undergoing.
Physical Geology
a major division of geology that examines the materials of Earth and seeks to understand the processes and forces acting upon Earth's surface from below.
Historical Geology
a major division of geology that deals with the origin of Earth and its development through time. Usually involves the study of fossils and their sequence in rock beds.
Hypothesis
a tentative explanation that is then tested to determine if it is valid.
Theory
a well-tested and widely accepted view that explains certain observable facts.
Catastrophism
the concept that Earth was shaped by catastrophic events of a short-term nature.
Uniformitarianism
the concept that the processes that have shaped Earth in the geological past are essentially the same as those operating today. "The present is the key to the past
Big Bang Theory
13.7 billion years ago, an incomprehensibly large explosion sent all matter of the universe flying outward at incredible speeds.
Nebular Hypothesis
States that the bodies of our solar system evolved from an enormous rotating cloud called the solar nebula.
Differentiation
Heavy elements sank to the center of the Earth and the light elements floated to the surface, causing the Earth to form the core/mantle/crust (chemically different).
Plate Tectonics
the theory that proposes Earth's outer shell consists of individual plates, which interact in various ways and thereby produce earthquakes, volcanoes, mountains, and the crust itself. (Three types are divergent, convergent and transform fault).
Lithosphere
the rigid outer layer of Earth, including the crust and upper mantle.
Asthenosphere
a subdivision of the mantle situation below the lithosphere. This zone of weak material exists below a depth of about 100 kilometers and in some regions extends as deep as 700 kilometers. The rock within this zone is easily deformed.
Divergent Plate Boundary
a boundary in which two plates move apart, resulting in upwelling of material from the mantle to create new seafloor.
Convergent Plate Boundary
a boundary in which two plates move together, resulting in oceanic lithosphere being thrust beneath an overriding plate, eventually to be reabsorbed into the mantle. It can also involve the collision of two continental plates to create a mountain system.
Transform Fault Boundary
a boundary in which two plates slide past one another without creating or destroying lithosphere.
Element
a substance that cannot be decomposed into simpler substances by ordinary chemical or physical means.
Atom
the smallest particle that exists as an element.
Proton
a positively charged subatomic particle found in the nucleus of an atom.
Neutron
a subatomic particle found in the nucleus of an atom. The neutron is electrically neutral, with a mass approximately equal to that of a proton.
Electron
a negatively charged subatomic particle that has a negligible mass and is found outside the atom's nucleus.
Atomic Number
the number of protons in the nucleus of an atom.
Atomic Mass
# of protons + # of neutrons. It's the number below the element symbol on the periodic table.
Isotope
Varieties of the same element that have different mass numbers; their nuclei contain the same number of protons but different numbers of neutrons.
Compound
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.
Ion
An atom or molecule that possesses an electrical charge.
Cation
Positively charged ion.
Anion
Negatively charged ion.
Ionic Bond
A chemical bond between two oppositely charged ions formed by the transfer of valence electrons from one atom to another.
Covalent Bond
A chemical produced by the sharing of electrons.
Mineral
A naturally occurring, inorganic crystalline material with a unique chemical structure.
Color
A phenomenon of light by which otherwise identical objects may be differentiated.
Streak
The color of a mineral in powdered form.
Luster
The appearance or quality of light reflected from the surface of a mineral.
Hardness
A mineral's resistance to scratching and abrasion.
Cleavage
The tendency of a mineral to break along planes of weak bonding.
Specific Gravity
The ratio of a substance's weight to the weight of an equal volume of water.
Rock Cycle
A model that illustrates the origin of the three basic rock types and the interrelatedness of Earth's materials and processes.
Igneous Rocks
A rock formed by the crystallization of molten magma.
Magma
A body of molten rock found at depth, including any dissolved gases and crystals.
Lava
Magma that reaches Earth's surface.
Extrusive
Igneous activity that occurs at Earth's surface.
Intrusive
Igneous rock that formed below Earth's surface.
Crystallization
The formation and growth of a crystalline solid from a liquid or gas.
Phaneritic
An igneous rock texture in which the crystals are reoughtly equal in size and large enough so that individual minerals can be identified with the unaided eye.
Aphanitic
A texture of igneous rocks in which the crystals are too small for individual minerals to be distinguished with the unaided eye.
Porphyritic
An igneous rock texture characterized by two distinctively different crystal sizes. The larger crystals are called phenocrysts, and the matrix of smaller crystals is termed the groundmass.
Vesicular
A term applied to aphanitic igneous rocks that contain many small cavities, called vesicles.
Glassy
A term used to describe the texture of certain igneous rocks, such as obsidian, that contain no crystals.
Felsic
A term derived from feldspar and silica (quartz). It is a term used to describe granitic igneous rocks.
Intermediate
Compositional category for igneous rocks found near the middle of Bowen's reaction series, mainly amphibole and the intermediate plagioclase feldspars.
Mafic
Because basaltic rocks contain a high percentage of ferromagnesian minerals, they are also called mafic (from magnesium and ferrum, the Latin name for iron).
Ultramafic
Compositional category for igneous rocks made up almost entirely of ferromagnesian minerals (mostly olivine and pyroxene).
Bowen's Reaction Series
A concept proposed by N.L. Bowen that illustrates the relationship between magma and the minerals crystallizing from it during the formation of igneous rock.
Fractional Crystallization
The process that separates magma into components having varied compositions and melting points.
Volcano
A mountain formed from lava and/or pyroclastics.
Viscosity (what affects it)
A measure of a fluids resistance to flow. Silicon affects it.
Fissure Eruption
An eruption in which lava is extruded from narrow fractures or cracks in the crust.
Shield Volcano
A broad, gently sloping volcano built from fluid basaltic lavas.
Pahoehoe
A lavas flow with a smooth-to-ropy surface.
Aa
A type of lava flow that has a jagged, blocky surface.
Pillow Lava
Basaltic lava that solidified in an underwater environment and develops a structure that resembles a pile of pillows.
Physical Geology
a major division of geology that examines the materials of Earth of Earth and seeks to understand the processes and forces acting upon Earth's surface from below.
Cinder Cone
A rather small volcano built primarily of pyroclastics ejected from a single vent.
Caldera
A large depression typically caused by collapse of the summit area of a volcano following a violent eruption.
Pluton
A structure that results from the emplacement and crystallization of magma beneath Earth's surface.
Tabular
Describing a feature such as an igneous pluton having two dimensions that are much longer than the third.
Massive
An igneous pluton that is not tabular in shape.
Concordant
A term used to describe intrusive igneous masses that form parallel to the bedding of the surrounding rock.
Discordant
A term used to describe plutons that cut across existing rock structures, such as bedding planes.
Partial Melting
The process by which most igneous rocks melt. Because 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
Intraplate
Igneous activity that occurs within a tectonic plate away from plate boundaries.
Weathering
The disintegration and decomposition of rock at or near the surface of Earth.
Erosion
The incorporation and transportation of material by a mobile agent, such as water, wind, or ice.
Mass Wasting
The downslope movement of rock, regolith, and soil under the direct influence of gravity.
Frost Wedging
The mechanical breakup of rock caused by the expansion of freezing water in cracks and crevices.
Exfoliation Domes
Large, dome-shaped structure, usually composed of granite, formed by sheeting.
Chemical Weathering
The processes by which the internal structure of a mineral is altered by the removal and/or addition of elements.
Soil
A combination of mineral and organic matter, water, and air; that portion of the regolith that supports plant growth.
Soil Profile
A vertical section through a soil showing its succession of horizons and the underlying parent material.
Solum
The O, A, and B horizon in a soil profile; living roots and other plant and animal life are largely confined to this zone.
Laterite Soil
A red, highly leached soil type found in the tropics and rich in oxides of iron and aluminum.
Metamorphism
The changes in mineral composition and texture of a rock subjected to high temperature and pressure within Earth.
Regional Metamorphism
Metamorphism associated with large-scale mountain building.
Contact Metamorphism
Changes in rock caused by the heat of a nearby magma body.
Foliated
A texture of metamorphic rocks that gives the rock a layered appearance.
Non-Foliated
Metamorphic rocks that do not exhibit foliation.
Parent Rock
The rock from which a metamorphic rock formed.