Initial Publication Date: March 3, 2006

Earth System Science Vocabularies Part IV:
Time and the Earth System

Measuring/Understanding Time

Principle of Uniformitarianism
The principle that the geological forces of the past differ neither in kind nor in energy from those now in operation. By its emphasis on the cumulative effect of slow actions over protracted periods of time, uniformitarianism implied a vast extension of geologic time.
The same forces presently in evidence acting over time with energies and frequencies similar to those now observable are the sufficient causes of all geologic records; related to episodicity; uniformitarianism with the caveat that rates are not necessarily constant
The doctrine that sudden violent, short-lived more or less worldwide events ouside our present experience or knowledge of nature have greatly modified the Earth's crust

Relative Time

Study of rock strata; original succession and age relations of rock strata; relations of their form, distribution, lithologic composition, fossil content, geophysical and geochemical properties and interpretation in terms of environment, mode of origin, and geologic history
The description and systematic organization of the rocks of the Earth's crust into distinctive named units based on the lithologic character of the rocks and their stratigraphic relations; var. volcanic stratigraphy
The approach to stratigraphy that utilizes the distribution of fossils in the stratigraphic record and the organization of strata into units of the basis of their contained fossils
sequence stratigraphy
The study of rock relationships within a chonostratigraphic framework of repetitive, genetically related strata bounded by surfaces of erosion or nondeposition or their correlative conformities
The approach to stratigraphy that utilizes the distribution of elemental and/or isotopic characteristics
A substantial break or gap in the geologic record where a rock unit is overlain by another that is not next in stratigraphic succession varieties: angular unconformity, disconformity, nonconformity, paraconformity
Law of Superposition
A general law upon which geologic chronology is based: in any sequence of layered rocks, sedimentary or volcanic, that has not been overturned or faulted the youngest stratum is at the top and the oldest at the base
Law of Original Horizontality
A general law of geology ;that acknowledges that water-laid sediments are deposited in strata that are horizontal or nearly horizontal, and parallel or nearly parallel to the Earth's surface
Law of Cross Cutting Relations
A stratigraphic principle whereby relative ages of rocks can be established: a rock (especially an igneous rock) is younger than any other rock across which it cuts
Law of Faunal Succession
A general law of geology that recognizes that fossil organisms (faunas and floras) succeed one another in a definite and recognizable order, each geologic formation having a different total aspect of life from that in the formations above it and below it; the relative age of rocks can be determined from their fossil content
facies (sedimentary)
Representing any areally restricted part of a designated stratigraphic unit which exhibits lithologic and paleontologic characters significantly different from those of another part or parts of the same unit
diachronous formations
A rock unit that is of varying age in different areas or that cuts across time planes or biozones

Biological (Methods for determining age)

biostratigraphy (fossil record)
The approach to stratigraphy that utilizes the distribution of fossils in the stratigraphic record and the organization of strata into units of the basis of their contained fossils
A method of geochronology based on the chemical racemization of amino acids; used to determine the elapsed time since an organism has died
Measurement of the diameter of lichens growing on exposed rock surfaces as a method of dating geomorphic features
growth ring
a. tree ring: Layer of wood produced in a tree or woody plant during its annual growth period seen in cross section as a ring and analyzed for chronologic and climatic data based on the number and relative sizes of the rings
b. growth rings in corals used to date a reef

Cyclic Phenomena

Milankovich cycles
Climatic changes result from fluctuations in the seasonal and geographic distribution of insolation, determined by variations of the Earth's orbital elements, namely eccentricity, tilt of rotational axis, and longitude of perihelion with periods on the order of 100,000 years, 41,000 years, and 23,000 years respectively that may appear in climatic and/or stratigraphic records
A sedimentary bed or lamina deposited in a body of still water within one year's time resulting from seasonal glacial cycles; counting and correlation of varves have been used to measure the depositional periods of Pleistocene glacial deposits

Physical Phenomena

hydration rinds (obsidian)
A method of calculating an age in years for an obsidian artifact or Holocene volcanic glass by determining the thickness of the hydration rim which has been produced by water molecules slowly diffusing into a fresh surface; applicable to glasses 200 to 200,000 years old
thermoluminscence dating
A method of dating applicable to materials that have once been heated (e.g. pottery, lava flows) or which have been exposed to ultraviolet light from the sun. A fraction of the energy released by decay of long-lived radioactive nuclides is stored as trapped electrons, and this energy is released as light upon heating. The age of a sample can be determined if the natural thermoluminescence is measured, the thermoluminescence induced by a known radiation dose is measured, and the radiation dose received the sample per unit time in the past is measured.

Quantitative Measurements of Time ("Absolute Time")

radiometric dating
Calculating an age in years for geologic materials by measuring the activity of a short-lived radioactive isotope (e.g. carbon-14); or by measuring the presence of a long-lived radioactive isotope plus its decay product
fission tracks
Damaged areas in a mineral produced by passage of atomic particles resulting from nuclear fission; the damage paths can be enlarged to microscopic size by etching techniques and used to determine an age for the material
cosmogenic nuclides
A nuclide produced by interaction with cosmic rays (e.g. 14N >14C); often used to data surfaces exposed to cosmic rays
paleomagnetic (stratigraphy)
The use of natural remanent magnetization directions to correlate stratigraphic sequences, depending on the polarity and/or paleosecular variation of the ambient magnetic field

Speedometers (and other terms with a temporal connotation)

(reference any Earth process that may operate on any scale e.g. rate of sea-floor spreading, mutation rate, strain rate)The quantity, amount or degree of something measured per unit of time (e.g. Km/hour)
The rate of flow (i.e. quantity) of mass, volume or energy per unit cross-sectional area normal to the direction of flow (e.g. mw/cm2/sec)
A sudden, violent disturbance of nature, ascribed to exceptional causes, affecting the physical conditions and the inhabitants of the Earth's surface
Geologic processes do not necessarily operate at steady state
A condition in which the rate of input of material or energy equals the rate of escape or loss
frequency (of Earth events)
A measure of rate of reccurrence of some phenomenon in time or space
mean residence time
The average amount of time a particular substance spends within a designated earth system or sub-system
reaction kinetics
Rates at which chemical reactions proceed

Evolution and History of the Earth

Evolution of Solid Earth

Process whereby small particles and gases in the solar nebula come together to form larger bodies, eventually of planetary size
impact (planetary)
A collision of two planetary bodies at or near cosmic velocity
Pertaining to lunar topographic features and lithologic map units constituting a system of rocks formed during the period of formation of the Mare Imbrium basin older than the post-mare craters and associated ejecta
Fe-catastrophe (core formation)
Early stages of planetary differentiation of Earth wherein radioactive heating of the planet's interior occurred faster than conduction could remove the heat resulting in melting of iron, and subsequent concentration of iron in the core
Planetary differentiation
The processes by which planets and satellites develop zones of different chemical and mineralogical composition; including formation of oceans, continents, atmosphere

Evolution of Atmosphere

anaerobic (primordial) atmosphere
Gas envelope without free oxygen; largely derived from volcanic emissions starting ca. 4.5-4.0 Ga; may contain water vapor, nitrogen, ammonia, methane and carbon dioxide
aerobic atmosphere
Free oxygen-bearing atmosphere, probably developed ca. 2.0 Ga ago through a combination of events a) photosynthesis, b) photodissociation of water, and c) the removal of carbon from the atmosphere to form organic matter


Late Ordovician
Planktonic organisms such as graptolites as well as benthic trilobites and brachiopods; a second wave of extinction impacted trilobite groups that had survived the first wave of extinction; corals, conodonts and bryozoans were similarly reduced in numbers and diversity
Late Devonian
Decimation of extensive Devonian reef communities
Late Permian-Triassic
Estimated that 90 percent of all existing marine species disappeared or were severely reduced; spore-bearing ferns and other plants gave way to gymnosperms
Extinction of dinosaurs possibly due to meteorite impact and consequent climatic change
Extinction of large mammals; decline and extinction ca. 8000 years ago; may be due to human overkill or to climatically controlled environmental changes

Evolution of the Continents

An early Proterozoic continent formed by welding of Archean shields (e.g. Superior, Wyoming, Hearne Provinces)
A supercontinent that existed from about 300 to 200 Ma ago and included most of the continental crust of the Earth; Gondwanaland and Laurasia were incorporated to form Pangea
The late Paleozoic continent of the modern southern hemisphere formed by the breakup of Pangea
The late Paleozoic continent in the northern hemisphere formed by the breakup of Pangea
Wopmay Orogen
A Paleoproterozoic orogen on the western margin of the Slave Province in Canada
Trans-Hudson Orogen
A Paleoproterozoic orogen that separates the Superior Province from the Hearne and Wyoming Provinces (among others)
Keweenawan Sequence
Middle Proterozoic, rift-related basaltic volcanics, in the upper midwest of the United States, ca. 1200-1000 Ma old
Grenville Orogeny
A major plutonic, metamorphic and deformational event in the Precambrian, ca. 1000-880 Ma, which affected a broad province along the southeastern border of the Canadian Shield; may reflect formation of Rodinian supercontinent
Caledonian Orogeny
Extends from the Canadian Maritime Privinces to northwestern England, northeastern Greenland and Norway late Silurian to earliest Devonian
Taconic Orogeny
An orogen of the latter part of the Ordovician period, well-developed through most of the northern Appalachians in the US and Canada
Acadian Orogeny
A middle Paleozoic deformation, especially in the northern Appalachians Late Devonian, but may have extended as late as 330 Ma
Antler Orogeny
An orogeny that extensively deformed Paleozoic rocks of the Great Basin in Nevada during the late Devonian and early Mississippian time
Hercynian Orogeny (Variscan Orogeny)
Late Paleozoic orogenic era of Europe, extending through the Carboniferous and Permian
Alleghany Orogeny
Late Paleozoic orogen, deformed the rocks of the Valley and Ridge province and those of the adjacent Allegheny Plateau in the central and southern Appalachians
Sonoma Orogeny
Deformation at or near the Permian-Triassic boundary from Alaska to Nevada collision of the Golconda arc with the Pacific margin of North America
Nevadan Orogeny
A time of deformation, metamorphism and plutonism during Jurassic and early Cretaceous time in the western part of the North American Cordillera
Sevier Orogeny
Deformation that occurred along the eastern edge of the Great Basin during times intermediate the Nevadan Orogeny farther west and the Laramide Orogeny farther east, culminating early in the Late Cretaceous; involving folding and eastward thrusting of the rocks; thin-skinned tectonics; decollement
Laramide Orogeny
Deformation in the eastern Rocky Mountains, USA, from late Cretaceous until the end of the Paleocene; intrusives and accompanying ore deposits emplaced about this time; "basement-cored" uplift, thick-skinned tectonics; high-angle reverse faults
Basin and Range Extension
Miocene and younger extension resulted in normal faulting from Nevada and western Utah southward into central Mexico, and north into Idaho and Montana
Colorado Plateau Uplift
Broad regional uplift during the Early to middle Pliocene (5-10 million years); "4 corners" area of the southwestern United States
Columbia Plateau
Broad volcanic plateau formed by massive outpouring of basalt during the late Tertiary and Quaternary in Washington, Oregon and Idaho
Yellowstone-Snake River Plain
Miocene to Holocene volcanic activity forming flood basalts of the Snake River Plain and the Yellowstone caldera

Glacial Stages

~2 million to 302 thousand years ago
Classical third glacial stage of the Pleistocene Epoch; ~302,000-132,000 years ago
Classical fourth glacial stage of the Pleistocene Epoch; 122,000-10,000 years ago

Geologic Time Scale

Precambrian Era, older than 3800 Ma.
Archean Eon
Pre-2500 Ma; older of two divisions of the Precambrian
Proterozoic Eon
2500-542 Ma; younger of the two divisions of the Precambrian. Ediacaran Fauna; A collective name for all Late Proterozoic faunas containing multicellular animal fossils, ca. 600 million years old
Phanerozoic Eon
Younger than Precambrian (e.g. 542 m. y. to present)
Paleozoic Era
Between the Proterozoic and Mesozoic, 542-251 Ma
Cambrian Period
ca. 542-488 Ma; the "Cambrian Explosion" of life with hard parts (exoskeletons)
Ordovician Period
ca. 488-433 Ma
Silurian Period
ca. 433-416 Ma; advent of land plants
Devonian Period
ca. 416-359 Ma; "Age of Fishes"
Mississippian Period
ca. 359-318 Ma
Pennsylvanian Period
ca. 318-299 Ma
Permian Period
ca. 299-251 Ma
Mesozoic Era
Between the Paleozoic and Cenozoic 245-66 Ma "Age of Dinosaurs"
Triassic Period
ca. 251-200 Ma
Jurassic Period
ca. 200-145 Ma
Cretaceous Period
ca. 145-66 Ma
Cenozoic Era
66 Ma to present; "Age of Mammals"
Tertiary Period
ca. 66-5 Ma
Paleocene Epoch
ca. 66-56 Ma
Eocene Epoch
ca. 56-34 Ma
Oligocene Epoch
ca. 34-23 Ma
Miocene Epoch
ca. 23-5 Ma
Pliocene Epoch
ca. 5-1.81 Ma
Quaternary Period
ca. 1.81-0 Ma; advent of humanoids
ca. 1.81 Ma—11,000 years b.p.
ca. 11,000 y.b.p to present; "post-glacial"