Geologic time scales. These are eras, periods, and epochs.
The eras are as follows:
Cenozoic
present to 65 million years BP
Mesozoic
65 to 230 million years BP
Paleozoic
230 to 570 million years BP
Precambrian
570 million to 4.5 billion years BP
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Glacial Till. Till is an unsorted glacial sediment. Part of glacial drift which was deposited directly by the glacier. May include a mix of particle sizes from clays to mixtures of clay, sand, gravel and boulders.
Glaciofluvial deposits. A land feature whose origin is related to the processes associated with glacial meltwater. Material moved by glaciers and subsequently sorted and deposited by streams flowing from the melting ice. The deposits are stratified and occur in the form of outwash plains, valley trains, deltas, kames, eskers, and kame terraces.
Glaciolacustrine deposits. Material ranging from fine clay to sand derived from glaciers and deposited in glacial lakes mainly by glacial meltwater. Many deposits are bedded or laminated.
Grassed waterway. A natural or constructed waterway, typically broad and shallow, seeded to grass as protection against erosion. Conducts surface water away from cropland.
The periods are as follows:
Quaternary
present to 2 million years BP
Tertiary
2 to 65 million years BP
Cretaceous
65 to 140 million years BP
Jurassic
140 to 190 million years BP
Triassic
190 to 230 million years BP
Permian
230 to 280 million years BP
Pennsylvanian
280 to 310 million years BP
Mississippian
310 to 345 million years BP
Devonian
345 to 405 million years BP
Silurian
405 to 425 million years BP
Ordovician
425 to 500 million years BP
Cambrian
500 to 570 million years BP
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Gravel. Rounded or angular fragments of rock as much as 3 inches (2 millimeters to 7.6 centimeters) in diameter. An individual piece is a pebble.
Great Group (soils) Each suborder is divided into great groups on the basis of close similarities in kind, arrangement, and degree of development of pedogenic horizons; soil moisture and temperature regimes; type of saturation; and base status. Each great group is identified by the name of a suborder and by a prefix that indicates a property of the soil. An example is Hapludalfs (Hapl, meaning minimal horizonation, plus udalf, the suborder of the Alfisols that has a udic soil moisture regime).
The epochs are as follows:
Recent (Holocene)
present to 10,000 years BP
Pleistocene
10,000 to 2 million years BP
Pliocene
2 to 10 million years BP
Miocene
10 to 25 million years BP
Oligocene
25 to 40 million years BP
Eocene
40 to 55 million years BP
Paleocene
55 to 65 million years BP
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Green manure crop (agronomy). A soil-improving crop grown to be plowed under in an early stage of maturity or soon after maturity.
Ground water. Generally, all subsurface water, as distinguished from surface water; specifically, that part of the subsurface water in the saturated zone (a zone in which all voids, large and small, ideally are filled with water under pressure greater than atmospheric).
Gully. A small channel with steep sides caused by erosion and cut in unconsolidated materials by concentrated but intermittent flow of water. The distinction between a gully and a rill is one of depth. A gully generally is an obstacle to farm machinery and is too deep to be obliterated by ordinary tillage; a rill is of lesser depth and can be smoothed over by ordinary tillage.
Hardpan. A hardened or cemented soil horizon, or layer. The soil material is sandy, loamy, or clayey and is cemented by iron oxide, silica, calcium carbonate, or other substance.
High-residue crops. Such crops as small grain and corn used for grain. If properly managed, residue from these crops can be used to control erosion until the next crop in the rotation is established. These crops return large amounts of organic matter to the soil.
Hill. A generic term for an elevated area of the land surface, rising as much as 1,000 feet (305 meters) above surrounding lowlands, commonly of limited summit area and having a well defined outline. Slopes are generally more than 15 percent. The distinction between a hill and a mountain is arbitrary and may depend on local usage.
Hillslope. A generic term for the steeper part of a hill between its summit and the drainage line, valley flat, or depression floor at the base of a hill.
Hydrologic Unit Area. A natural drainage basin or hydrologic area that includes either the drainage area of a major river or the combined drainage areas of a series of rivers.
Hyperthermic soils. The mean annual soil temperature is 22 C or higher, and the difference between mean summer and mean winter soil temperatures is more than 6 C either at a depth of 50 cm.
Igneous rock. Rock that was formed by cooling and solidification of magma and that has not been changed appreciably by weathering since its formation. Major varieties include plutonic and volcanic rock (e.g., andesite, basalt, and granite).
Industrial water use. Use of water for fabrication, processing, washing, and cooling in industries involved with chemical and allied products, food, mining, paper and allied products, petroleum refining, and steel.
Interfluve. A landform composed of the relatively undissected upland or ridge between two adjacent valleys containing streams flowing in the same general direction. An elevated area between two drainageways that sheds water to those drainageways.
Irrigation. Application of water to soils to assist in the production of crops and pasture or to maintain plant growth in recreational areas, such as parks and golf courses.
Isofrigid soils. could also have a cryic temperature regime.The mean annual soil temperature is lower than 8 C. A few with organic materials in the upper part are exceptions. A soil temperature regime with the prefix iso: the mean summer and mean winter soil temperatures differ by less than 6 C at a depth of 50 cm.
Isohyperthermic soils. The mean annual soil temperature is 22 C or higher.
Isomesic soils. The mean annual soil temperature is 8 C or higher but lower than 15 C.
Isothermic soils. The mean annual soil temperature is 15 C or higher but lower than 22 C.