# Geologic record > Mediated Wiki article. Canonical URL: https://mediated.wiki/source/Geologic_record > Markdown URL: https://mediated.wiki/source/Geologic_record.md > Source: https://en.wikipedia.org/wiki/Geologic_record > Source revision: 1351815863 > License: Creative Commons Attribution-ShareAlike 4.0 International (https://creativecommons.org/licenses/by-sa/4.0/) {{Short description|Entirety of the layers of rock strata}} {{Redirect|Rock records|the Taiwanese record label|Rock Records}} thumb|The layer cake like appearance of concordant strata laid down over hundreds of thousands of years (in northern Spain) [[Image:End of cobbles.jpg|thumb|Strata turned sideways by [orogenic](/source/Orogeny) forces near [San Sebastián](/source/San_Sebasti%C3%A1n), [Spain](/source/Spain)]] The '''geologic record,''' in [stratigraphy](/source/stratigraphy), [paleontology](/source/paleontology) and other [natural sciences](/source/natural_sciences), is the entirety of the layers of rock [strata](/source/stratum) - deposits laid down by [volcanism](/source/volcanism) or by [deposition of sediment](/source/Deposition_(sediment)) derived from [weathering](/source/weathering) detritus ([clay](/source/clay)s, [sand](/source/sand)s etc.). This includes all its [fossil](/source/fossil) content and the information it yields about the history of the Earth: its past [climate](/source/climate), geography, geology and the [evolution](/source/evolution) of life on its surface. According to the [law of superposition](/source/law_of_superposition), [sedimentary](/source/Sedimentary_rock) and [volcanic](/source/volcanic_rock) rock layers are deposited on top of each other. They harden over time to become a solidified ([competent](/source/Competence_(geology))) rock column, that may be intruded by [igneous rock](/source/igneous_rock)s and disrupted by [tectonic](/source/tectonic) events. ==Correlating the rock record== [[Image:Horseshoe Canyon Alberta Nov 1988.jpg|thumb|Horseshoe Canyon Formations exposed in [Horseshoe Canyon](/source/Horseshoe_Canyon_(Alberta)) near [Drumheller](/source/Drumheller), [Alberta](/source/Alberta)]] At a certain locality on the Earth's surface, the rock column provides a [cross section](/source/Cross_section_(geometry)) of the [natural history](/source/natural_history) in the area during the time covered by the age of the rocks. This is sometimes called the ''rock history'' and gives a window into the natural history of the location that spans many geological time units such as ages, epochs, or in some cases even multiple major [geologic periods](/source/period_(geology))—for the particular [geographic](/source/geography) region or regions. The geologic record is in no one place entirely complete{{Citation| author = Committee on the Geologic Record of Biosphere Dynamics, Board on Earth Sciences and Resources, Board on Life Sciences, Division on Earth and Life Studies, National Research Council| year = 2005| title = The Geological Record of Ecological Dynamics: Understanding the Biotic Effects of Future Environmental Change| publisher = National Academies Press| page = 14| isbn = 9780309095808| url = https://books.google.com/books?id=4gNzGoih00YC&q=incomplete+geologic+record&pg=PA14}} for where geologic forces one [age](/source/age_(geology)) provide a low-lying region accumulating [deposits](/source/stratum) much like a layer cake, in the next may have uplifted the region, and the same area is instead one that is [weathering](/source/weathering) and being torn down by chemistry, wind, temperature, and water. This is to say that in a given location, the geologic record can be and is quite often interrupted as the ancient local environment was converted by geological forces into new [landform](/source/landform)s and features. Sediment core data at the mouths of large riverine [drainage basin](/source/drainage_basin)s, some of which go {{convert|7|mi}} deep thoroughly support the law of superposition.{{clarify|date=December 2019|What is the law of superposition?}} However using broadly occurring deposited layers trapped within differently located rock columns, geologists have pieced together a system of units covering most of the [geologic time scale](/source/geologic_time_scale) using the law of superposition, for where [tectonic forces](/source/tectonics) have uplifted one ridge newly subject to [erosion](/source/erosion) and [weathering](/source/weathering) in [folding](/source/Fold_(geology)) and [faulting](/source/Fault_(geology)) the strata, they have also created a nearby trough or [structural basin](/source/structural_basin) region that lies at a relative lower elevation that can accumulate additional deposits. By comparing overall formations, geologic structures and local strata, calibrated by those layers which are widespread, a nearly complete geologic record has been constructed since the 17th century. ==Discordant strata example== thumb|left|USGS correlation diagram Correcting for discordancies can be done in a number of ways and utilizing a number of technologies or field research results from studies in other disciplines. In this example, the study of layered rocks and the fossils they contain is called [biostratigraphy](/source/biostratigraphy) and utilizes amassed [geobiology](/source/geobiology) and [paleobiological](/source/paleobiology) knowledge. Fossils can be used to recognize rock layers of ''the same or different [geologic ages](/source/age_(geology))'', thereby coordinating locally occurring [geologic stages](/source/stage_(geology)) to the overall [geologic timeline](/source/geologic_time_scale). The pictures of the fossils of monocellular algae in this [USGS](/source/United_States_Geological_Survey) figure were taken with a scanning electron microscope and have been magnified 250 times. In the U.S. state of [South Carolina](/source/South_Carolina) three marker species of fossil algae are found in a core of rock whereas in [Virginia](/source/Virginia) only two of the three species are found in the [Eocene](/source/Eocene) [Series](/source/series_(geology)) of rock layers spanning three [stages](/source/stage_(geology)) and the geologic ages from 37.2–55.8 [MA](/source/Year). Comparing the record about the discordance in the record to the full rock column shows the non-occurrence of the missing species and that portion of the local ''rock record'', from the early part of the middle Eocene is missing there. This is one form of discordancy and the means geologists use to compensate for local variations in the rock record. With the two remaining marker species it is possible to [correlate](/source/correlate) rock layers of the same age (early Eocene and latter part of the middle Eocene) in both South Carolina and Virginia, and thereby "calibrate" the local rock column into its proper place in the overall geologic record. {{Geology to Paleobiology|none=yes}} ==Lithology vs paleontology== Consequently, as the picture of the overall rock record emerged, and discontinuities and similarities in one place were cross-correlated to those in others, it became useful to subdivide the overall geologic record into a series of component sub-sections representing different sized groups of layers within known geologic time, from the shortest time span [stage](/source/stage_(geology)) to the largest thickest strata [eonothem](/source/eonothem) and time spans [eon](/source/eon_(geology)). Concurrent work in other natural science fields required a time continuum be defined, and earth scientists decided to coordinate the system of rock layers and their identification criteria with that of the geologic time scale. This gives the pairing between the physical layers of the left column and the time units of the center column in the table at right. ==Gallery== File:Dinosaur Provincial Park 19.jpg|Well-[stratified](/source/stratum) and fully exposed sedimentary formations in Dinosaur Provincial Park, [Alberta](/source/Alberta), [Canada](/source/Canada)) extend over large areas exposing [eons](/source/eon_(geology)) of rock history through numerous wind and water exposed [strata layers](/source/stratum) Image:Gentilly, New Orleans Hurricane Katrina Levee Failure Flood Aftermath - Deep Silt Off Mirabeau.jpg|[New Orleans](/source/New_Orleans) after [Hurricane Katrina](/source/Hurricane_Katrina): Unlithified sediment layers laid down in historic times. This cut was an attempt to find bedrock near a residential street near the lower breach of the [London Avenue Canal](/source/London_Avenue_Canal) after restoring the levees which has been plowed/excavated clear by the Army Corps of Engineers, showing a nascent stratigraphy in the large deposits of silt deposited by flooding in recent earth history. Image:Tremp formatie.jpg|Three eras of deposition and two discordances are visible in this highway cut in the Netherlands. Note the color and slight angular change between the lower red bed layering and the middle strata. The upper strata are tilted yet again relative to the bottom layerings well demonstrating the cycles this land formation went through as part of the sea floor. Image:Péry-Reuchenette Oxfordian.JPG|Oxfordian (Upper Jurassic) cyclic sediments at Péry-Reuchenette, near Tavannes, Bern canton, Switzerland. Alternating layers are [limestone](/source/limestone) (light, more competent) and [marl](/source/marl)/[clay](/source/clay); dominant cycle is the 200,000 year-cycle. Image:Time-Honored Rockfall.jpg|An ancient rockfall which protected the rock records beneath its impact site from further large scale erosion. Taken along Burr Trail, [Grand Staircase–Escalante National Monument](/source/Grand_Staircase%E2%80%93Escalante_National_Monument), Utah, US. Image:PS2492-2 0017-1298 photo.jpg|Sediment core, taken with a gravity corer by the research vessel POLARSTERN in the South Atlantic; light/dark-coloured changes are due to climatic variation of the [Quaternary](/source/Quaternary); basis age of the core is about 1 million years. ==References== {{reflist}} {{Earth}} {{DEFAULTSORT:Geologic Record}} Category:Historical geology Category:Geologic time scales of Earth Category:Geochronology Category:Stratigraphy --- Adapted from the Wikipedia article [Geologic record](https://en.wikipedia.org/wiki/Geologic_record) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Geologic_record?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.