Geology and Soil Vocabulary

soil
Complex mixture of inorganic minerals (clay, silt, pebbles, and sand), decaying organic matter, water, air, and living organisms.
soil horizons
Horizontal zones that make up a particular mature soil. Each horizon has a distinct texture and composition that vary with different types of soils. See soil profile.
soil permeability
Rate at which water and air move from upper to lower soil layers. Compare porosity.
soil porosity
See porosity.
soil profile
Cross-sectional view of the horizons in a soil. See soil horizon.
soil structure
How the particles that make up a soil are organized and clumped together. See also soil permeability, soil texture.
soil texture
Relative amounts of the different types and sizes of mineral particles in a sample of soil.
porosity
Percentage of space in rock or soil occupied by voids, whether the voids are isolated or connected. Compare permeability.
permeability
The degree to which underground rock and soil pores are interconnected and thus a measure of the degree to which water can flow freely from one pore to another. Compare porosity.
percolation
Passage of a liquid through the spaces of a porous material such as soil.
loams
Soils containing a mixture of clay, sand, silt, and humus. Good for growing most crops.
leaching
Process in which various chemicals in upper layers of soil are dissolved and carried to lower layers and, in some cases, to groundwater.
infiltration
Downward movement of water through soil.
core
Inner zone of the earth. It consists of a solid inner core and a liquid outer core. Compare crust, mantle.
convergent plate boundary
Area where earth’s lithospheric plates are pushed together. See subduction zone. Compare divergent plate boundary, transform fault.
crust
Solid outer zone of the earth. It consists of oceanic crust and continental crust. Compare core, mantle.
divergent plate boundary
Area where earth’s lithospheric plates move apart in opposite directions. Compare convergent plate boundary, transform fault.
earthquake
Shaking of the ground resulting from the fracturing and displacement of rock, which produces a fault, or from subsequent movement along the fault.
erosion
Process or group of processes by which loose or consolidated earth materials are dissolved, loosened, or worn away and removed from one place and deposited in another. See weathering.
geology
Study of the earth’s dynamic history. Geologists study and analyze rocks and the features and processes of the earth’s interior and surface.
igneous rock
Rock formed when molten rock material (magma) wells up from the earth’s interior, cools, and solidifies into rock masses. Compare metamorphic rock, sedimentary rock. See rock cycle.
lithosphere
Outer shell of the earth, composed of the crust and the rigid, outermost part of the mantle outside the asthenosphere; material found in earth’s plates. See crust, mantle.
magma
Molten rock below the earth’s surface.
mantle
Zone of the earth’s interior between its core and its crust. Compare core, crust. See lithosphere.
metamorphic rock
Rock produced when a preexisting rock is subjected to high temperatures (which may cause it to melt partially), high pressures, chemically active fluids, or a combination of these agents. Compare igneous rock, sedimentary rock. See rock cycle.
mineral
Any naturally occurring inorganic substance found in the earth’s crust as a crystalline solid. See mineral resource.
plate tectonics
Theory of geophysical processes that explains the movements of lithospheric plates and the processes that occur at their boundaries. See lithosphere, tectonic plates.
rock
Any material that makes up a large, natural, continuous part of the earth’s crust. See mineral.
rock cycle
Largest and slowest of the earth’s cycles, consisting of geologic, physical, and chemical processes that form and modify rocks and soil in the earth’s crust over millions of years.
sedimentary rock
Rock that forms from the accumulated products of erosion and in some cases from the compacted shells, skeletons, and other remains of dead organisms. Compare igneous rock, metamorphic rock. See rock cycle.
subduction zone
Area in which oceanic lithosphere is carried downward (subducted) under the island arc or continent at a convergent plate boundary. A trench ordinarily forms at the boundary between the two converging plates. See convergent plate boundary.
tectonic plates
Various-sized areas of the earth’s lithosphere that move slowly around with the mantle’s flowing asthenosphere. Most earthquakes and volcanoes occur around the boundaries of these plates. See lithosphere, plate tectonics.
transform fault
Area where the earth’s lithospheric plates move in opposite but parallel directions along a fracture (fault) in the lithosphere. Compare convergent plate boundary, divergent plate boundary.
tsunami
Series of large waves generated when part of the ocean floor suddenly rises or drops, usually because of an earthquake.
volcano
Vent or fissure in the earth’s surface through which magma, liquid lava, and gases are released into the environment.
weathering
Physical and chemical processes in which solid rock exposed at earth’s surface is changed to separate solid particles and dissolved material, which can then be moved to another place as sediment. See erosion.