Pertaining to geochronology.
A division of time traditionally distinguished on the basis of the rock
record as expressed by a time-stratigraphic unit. Geochronologic units in
order of decreasing rank are eon, era, period, epoch, and age. Names of
periods and units of lower rank are the same as those of the corresponding
time-stratigraphic units; the names of some eras and eons are
independently formed. Syn:geologic time unit
The study of time in relationship to the history of the Earth, esp. by the
absolute age determination and relative dating systems developed for this
purpose. See also:absolute time
Syn:geologic chronology
Measurement of geologic time by geochronologic methods, esp. radiometric
dating. CF:geochronology
An obsolete syn. of geochronology. AGI
a. A hollow globular or subspherical body, from 2.5 to 30 cm or more in
diameter, found in certain limestone beds and rarely in shales; it is
characterized by a thin and sometimes incomplete outermost primary layer
of dense chalcedony, by a cavity that is partly filled by a drusy lining
of inward-projecting crystals (usually of quartz or calcite and sometimes
of barite, celestite, and various sulfides) deposited from solution on the
cavity walls. Unlike a druse, a geode is separable (by weathering) as a
discrete nodule or concretion from the rock in which it occurs and its
inner crystals are not of the same minerals as those of the enclosing
rock. AGI
b. The crystal-lined cavity in a geode. AGI
c. A term applied to a rock cavity and its lining of crystals that is not
separable as a discrete nodule from the enclosing rock. CF:vug
AGI
a. The science concerned with the determination of the size and shape of
the Earth and the precise location of points on its surface. AGI
b. The determination of the gravitational field of the Earth and the study
of temporal variations such as Earth tides, polar motion, and rotation of
the Earth. Syn:geodetics
Quantities defining the horizontal position of a point on an ellipsoid of
reference with respect to a specific geodetic datum, usually expressed as
latitude and longitude. These may be referred to as geodetic positions or
geographic coordinates. The elevation of a point is also a geodetic
coordinate and may be referred to as a height above sea level. AGI
See:geodesy
Surveying in which account is taken of the figure and size of the Earth
and corrections are made for Earth curvature; the applied science of
geodesy. It is used where the areas or distances involved are so great
that results of desired accuracy and precision cannot be obtained by plane
surveying. AGI
Trade name of an electronic optical device that measures ground distances
precisely by electronic timing and phase comparison of modulated light
waves that travel from a master unit to a reflector and return to a
light-sensitive tube where an electric current is set up. It is normally
used at night and is effective with first-order accuracy up to distances
of 3 to 25 miles (5 to 40 km). Etymol: acronym for geodetic-distance
meter. CF:tellurometer
Pertaining to physical processes within the Earth as they affect the
features of the crust. AGI
An 18th-century term for a science accounting for the origin,
distribution, and sequence of minerals and rocks in the Earth's crust. The
term was superseded by geology as early ideas were abandoned. It has
become restricted to absolute knowledge of the Earth, as distinct from the
theoretical and speculative reasoning of geology. AGI
The ratio of face length (X) to length of main haulage roads (L) in the
same units; i.e., X/L. See also:concentration of output
See:cycle of erosion
A computer system for managing spatial data. Abbrev. GIS. A GIS, e.g., can
provide a simultaneous consideration of geology, geophysics, geochemistry,
and mineral deposits in a region for the purposes of mineral exploration.
Bonham-Carter
The study of all aspects of the Earth's surface including its natural and
political divisions, the distribution and differentiation of areas, and
often, people in relationship to their environment. AGI
A term, often used interchangeably with hydrogeology, referring to the
hydrologic or flow characteristics of subsurface waters. AGI
The figure of the Earth considered as a sea-level surface extended
continuously through the continents. It is a theoretically continuous
surface that is perpendicular at every point to the direction of gravity
(the plumb line). It is the reference for astronomical observations and
for geodetic leveling. See also:datum
See:isogeotherm
See:geological