What Does the Law of Superposition Do

In a very simple way, the law of superposition states that if there is geological stratification, the first layers deposited or formed will be the oldest, followed by the younger ones that will form over time due to ever more recent deposits. But the condition for this law to be true is that the layers of the rock must not be deformed due to any of the exogenous processes such as weathering and erosion. This is the most important concept in stratigraphic dating, but it assumes that the law of superposition is true and that the layer formed by deposition cannot be older than the mineral content of the layer/layer. A common goal of stratigraphic studies is to divide a sequence of rock layers into verifiable units, determine the temporal relationships involved, and correlate units of the sequence – or the entire sequence – with rock layers elsewhere. After the unsuccessful attempts of the International Geological Congress (IGC; founded in 1878) in the second half of the 19th century to standardize a stratigraphic scale, the International Union of Geological Sciences (IUGS; founded in 1961) established a commission on stratigraphy to work towards this goal. Traditional stratigraphic schemes are based on two scales: (1) a time scale (using eons, epochs, periods, epochs, ages and chronicles), for which each unit is defined by its starting and ending points, and (2) a correlated scale of rock sequences (using systems, series, stages and chronozones). These schemes, when used in conjunction with other dating methods – such as radiometric dating (the measurement of radioactive decay), paleoclimatic dating and paleomagnetic determinations – generally developed in the second half of the 20th century, have led to slightly less confusion of nomenclature and increasingly reliable information on which to base conclusions about Earth`s history. The law of superposition is an axiom that constitutes one of the foundations of the sciences of geology, archaeology and other areas of geological stratigraphy. In its simplest form, it indicates that in undistorted stratigraphic sequences, the oldest layers are at the bottom of the sequence, while new material accumulates on the surface to form new deposits over time. This is of paramount importance for stratigraphic dating, which requires a number of assumptions, including the fact that the law of superposition applies and that an object cannot be older than the materials it is made of.

To illustrate the practical applications of layering in scientific research, sedimentary rocks that have not been deformed by more than 90° will have the oldest layers on the ground, allowing paleontologists and paleobotanists to identify the relative age of all fossils found in the layers, with the remains of the most archaic life forms being limited to the lowest. These results can inform the community about the fossil record covering relevant strata to determine which species coexisted over time and which species existed successively in a potentially evolutionary or phylogenetically relevant way. The law of superposition states that in each of the undisturbed rock sequences deposited in layers, the youngest layer will always be at the top and the oldest layer will always be below. The best example of the law of superposition is one of the sedimentary rocks that are not deformed because sedimentary rocks are formed by the deposition of various minerals and rock fragments. In many cases, the law of superposition can be considered the most important basic principle behind a particular feature, rather than the sole explanation. For example, the shape of rivers can be explained by a combination of the law of superposition and the law of development of sedimentary basins. Stratification behaves differently with magmatic deposits formed on the surface such as lava flows and ash falls, and therefore layering cannot always be successfully applied under certain conditions. The overlap in archaeology, and in particular in the use of stratification during excavations, is somewhat different, as the processes of deposition of archaeological layers are somewhat different from geological processes. Human interventions and activities in the archaeological record do not have to be formed chronologically from top to bottom or to be deformed from the horizontal, as are natural layers by equivalent processes. Some archaeological layers (often called contexts or layers) are created by undermining the earlier layers. An example would be that backfilling of sludge from an underground drain would form some time after the ground immediately above.

Other examples of non-vertical overlay would be changes to standing structures such as creating new doors and windows in a wall. Overlay in archaeology requires a number of interpretations to correctly identify chronological sequences, and in this sense, overlay in archaeology is more dynamic and multidimensional. Thus, the law of superposition proves to be a useful tool for determining the interrelationship between the different layers of the soil according to their respective ages. It is an integral part of modern geology and other natural sciences. One of the most important limitations of the law of superposition in geology is that the sedimentary rocks studied must not be deformed or at least not deformed beyond 90°. The original stratification achieved by various natural processes can be disturbed and distorted by a number of factors, including interference from animals and vegetation and crystallization of limestone, as these processes contribute to the alteration and erosion of layers over a significant period of time. The reason why the law of superposition mainly affects sedimentary rocks is that these rocks are formed by the deposition of rock fragments and minerals over a period of time. Such a stratification scheme may not be the same for surface-forming igneous rock deposits as lava flows and ash falls. Therefore, overlay geology may not be successfully applicable under these conditions. The law of superposition makes logical sense, but in practice it is the nature of the fossils found in the sedimentary layers that determines the relative age of the rocks.

The theory of descent with modification prevails over the empirical proof of superposition. The law of superposition is one of the most fundamental principles of stratigraphy – the branch of archaeology that studies the geological layers of earth and soil. It has been shown that this law makes it possible to accurately determine the relative age of the different layers of the soil. The time has come to test our understanding of this law. The following is a small worksheet with two examples of problems whose solutions can be derived by applying the superposition law, similar to what is taught at the University of Wisconsin to better understand the concept. As this process progresses, many years later, several layers of soil form on top of each other at the repository site, just like the cards in a deck.