a fossil that is useful for dating and correlating the strata in which it is found.
Radiometric age dating
any method of determining the age of earth materials or objects of organic origin based on measurement of either short-lived radioactive elements or the amount of a long-lived radioactive element plus its decay product
Isotopes
each of two or more forms of the same element that contain equal numbers of protons but different numbers of neutrons in their nuclei, and hence differ in relative atomic mass but not in chemical properties; in particular, a radioactive form of an element.
Half-life
the time taken for the radioactivity of a specified isotope to fall to half its original value.
Contour lines
a line on a map joining points of equal height above or below sea level.
Index contour
a contour line that is thicker than the rest and usually labeled with the elevation that it represents
Relief
difference in elevation between any two points
Regional relief
the difference in elevation between the highest and lowest points on a topographic map
Gradient
the degree of inclination
Benchmark
a mark on a permanent object indicating elevation and serving as a reference in topographic surveys and tidal observations
Strike
a line representing the intersection of that feature with a horizontal plane
Dip
the angle at which a planar feature is inclined to the horizontal plane
Structural geology
the study of the three-dimensional distribution of rock units with respect to their deformational histories.
Topographic profile
a cross sectional view along a line drawn through a portion of a topographic map
Geologic cross-section
An interpretation of a vertical section through the Earth's surface, most usefully a profile, for which evidence was obtained by geologic and geophysical techniques or from a geologic map
Block diagrams
a three-dimensional drawing representing a block of the earth's crust, showing geological structure
Anticline
a fold that is convex up and has its oldest beds at its core
Syncline
a fold with younger layers closer to the center of the structure.
Monocline
a bend in rock strata that are otherwise uniformly dipping or horizontal.
Dome
a feature in structural geology consisting of symmetrical anticlines that intersect each other at their respective apices
basin
a large low-lying area
P-wave
a longitudinal earthquake wave that travels through the interior of the earth and is usually the first conspicuous wave to be recorded by a seismograph