The law of superposition is an axiom that forms one of the bases of the sciences of

geology Geology () is a branch of natural science concerned with Earth and other Astronomical object, astronomical objects, the features or rock (geology), rocks of which it is composed, and the processes by which they change over time. Modern geology ...

archaeology Archaeology or archeology is the scientific study of human activity through the recovery and analysis of material culture. The archaeological record consists of artifacts, architecture, biofacts or ecofacts, sites, and cultural landsc ...

, and other fields pertaining to geological

stratigraphy Stratigraphy is a branch of geology concerned with the study of rock layers ( strata) and layering (stratification). It is primarily used in the study of sedimentary and layered volcanic rocks. Stratigraphy has three related subfields: lithost ...

. In its plainest form, it states that in undeformed stratigraphic sequences, the oldest

strata In geology and related fields, a stratum ( : strata) is a layer of rock or sediment characterized by certain lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by visible surfaces known as e ...

will lie at the bottom of the sequence, while newer material stacks upon the surface to form new deposits over time. This is paramount to stratigraphic dating, which requires a set of assumptions, including that the law of superposition holds true and that an object cannot be older than the materials of which it is composed. To illustrate the practical applications of superposition in scientific inquiry, sedimentary rock that has not been deformed by more than 90° will exhibit the oldest layers on the bottom, thus enabling paleontologists and paleobotanists to identify the relative ages of any fossils found within the strata, with the remains of the most archaic lifeforms confined to the lowest. These findings can inform the community on the fossil record covering the relevant strata, to determine which species coexisted temporally and which species existed successively in perhaps an evolutionarily or

phylogenetically In biology, phylogenetics (; from Greek φυλή/ φῦλον [] "tribe, clan, race", and wikt:γενετικός, γενετικός [] "origin, source, birth") is the study of the evolutionary history and relationships among or within groups ...

relevant way.

History

The law of superposition was first proposed in 1669 by the Danish scientist

Nicolas Steno Niels Steensen ( da, Niels Steensen; Latinized to ''Nicolaus Steno'' or ''Nicolaus Stenonius''; 1 January 1638 – 25 November 1686William "Strata" Smith, who used it to produce the first geologic map of Britain.Patrick Wyse Jackson, ''The Chronologers' Quest: The Search for the Age of the Earth'', Cambridge University Press, 2006 , pp.127-8. It is the first of Smith's laws, which were formally published in ''Strata Identified by Fossils'' (1816–1819).

Archaeological considerations

Superposition in archaeology and especially in stratification use during

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is slightly different as the processes involved in laying down archaeological strata are somewhat different from geological processes. Man-made intrusions and activity in the archaeological record need not form chronologically from top to bottom or be deformed from the horizontal as natural strata are by equivalent processes. Some archaeological strata (often termed as contexts or layers) are created by undercutting previous strata. An example would be that the silt back-fill of an underground drain would form some time after the ground immediately above it. Other examples of non vertical superposition would be modifications to standing structures such as the creation of new doors and windows in a wall. Superposition in

requires a degree of interpretation to correctly identify chronological sequences and in this sense superposition in archaeology is more dynamic and multi-dimensional.

Other limitations to stratification and superposition

Original stratification induced by natural processes can subsequently be disrupted or permutated by a number of factors, including animal interference and vegetation, as well as limestone crystallization. Stratification behaves in a different manner with surface-formed igneous depositions, such as lava flows and ash falls, and thus superposition may not always successfully apply under certain conditions.

References

General sources

*Hamblin, W.K. ''The Earth's Dynamic Systems: A Textbook in Physical Geology,'' by W. Kenneth Hamblin, BYU, Provo, UT, Illus. William L. Chesser, Dennis Tasa, (Burgess Publishing Company, Minneapolis, Minnesota), c 1978, pg. 115, "The Principle of Superposition and Original Horizontality;" pg. 116: The Law of Faunal Succession, "The Principle of Crosscutting Relations;" pg 116-17: "The Principle of Inclusion," (as in the Steno discussion above). *Principles of Archaeological Stratigraphy. 40 figs. 1 pl. 136 pp. London & New York: Academic Press {{Geologic Principles Dating methods Geological history of Earth Stratigraphy

History

Archaeological considerations

Other limitations to stratification and superposition

See also

References

General sources