Chapter 8: Time and Geology Definitions
Terms in this set (39)
The principle that the same processes and natural laws that operated in the past are those we can actually observe or infer from observations as operating at present. Under present usage, uniformitarianism has the same meaning as actualism for most geologists.
An unconformity in which younger strata overlie an erosion surface on tilted or folded layer rock.
The oldest eon of Earth's history.
The most recent of the eras; followed the Mesocoiz Era.
Boundary surface between two different rock types or ages of rocks.
In geology, correlation usually means determining time equivalency of rock units. Rock units may be correlated within a region, a continent, and even between continents.
A principle or law stating that a disrupted pattern is older than the cause of disruption.
A surface that represents missing rock strata but beds above and below that surface are parallel to one another.
The largest unit of geologic time.
Each period of the standard geologic time scale is divided into epochs (e.g., Pleistocene Epoch of the Quaternary Period).
Major subdivision of the standard geologic time scale (e.g., Mesozoic Era).
A principle or law stating that fossil species succeed one another in a definite and recognizable order; in general, fossils in progressively older rock show increasingly greater differences from species living at present.
A body of rock of considerable thickness that has a recognizable unity or similarity making it distinguishable from adjacent rock units. Usually composed of one or bed or several beds of sedimentary rock, although the term is also applied to units of metamorphic and igneous rock. A convenient unit for mapping, describing, or interpreting the geology of a region.
The oldest eon.
The time it takes for a given amount of a radioactive isotope to be reduced by one-half.
Holocene (or Recent) Epoch
The youngest epoch, which began around 10,000 years ago and it continuing presently.
A fragment of rock that is distinct from the body of igneous rock in which it is enclosed.
A fossil from a very short-lived species known to have existed during a specific period of geologic time.
Atoms (of the same element) that have different numbers of neutrons but the same number of protons.
Determining the age of a rock or mineral through its radioactive elements and decay products (previously and somewhat inaccurately called radiometric or radioactive dating).
Principle that states an original sedimentary layer extends laterally unit it tapers or thins at its edges.
The era that followed the Paleozoic Era and preceded the Cenozoic Era.
An unconformity in which an erosion surface on plutonic or metamorphic rock has been converged by younger sedimentary or volcanic rock.
Age given in years or some other unit of time.
The deposition of most water-laid sediment in horizontal or near-horizontal layers that are essentially parallel to Earth's surface.
The era that followed the Precambrian and began with the appearance of complex life, as indicated by fossils.
Each era of the standard geologic time scale is subdivided into periods (e.g., the Cretaceous Period).
Eon of geologic time. Includes all time following the Precambrian.
Being able to physically follow a rock unity between two places.
An epoch of the Quaternary Period characterized by several glacial ages.
The vast amount of time that preceded the Paleozoic Era.
Eon of Precambrian time.
The youngest geologic period; includes the present time.
The spontaneous nuclear disintegration of certain isotopes.
The sequence in which events took place (not measured in time units).
Standard Geologic Time Scale
A worldwide relative scale of geologic time divisions.
A principle or law stating that within a sequence of undistributed sedimentary rocks, the oldest layers are on the bottom, the youngest on the top.
A surface that represents a break in the geologic record, with the rock unit immediately above it being considerably younger than the rock beneath.
Principle that geologic processes operating at present are the same processes operating at present are the same processes that operated in the past. The principle is stated more succinctly as, "The present is the key to the past."
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