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For other uses, see Superposition.
A stratigraphic section of Jurassic rock exposed in Makhtesh Gadol, Israel. Since there is no overturning, the rock at the bottom is older than the rock on the top by the Principle of Superposition.
A stratigraphic section of Jurassic rock exposed in Makhtesh Gadol, Israel. A makhtesh (מכתש plural מכתשים - "makhteshim" is a geological landform regarded to be unique to the Negev desert of Israel and the Since there is no overturning, the rock at the bottom is older than the rock on the top by the Principle of Superposition.

The law of superposition (or the principle of superposition) is an observation that is a foundational principle of sedimentary stratigraphy:

Sedimentary layers are deposited in a time sequence, with the oldest on the bottom and the youngest on the top. Stratigraphy, a branch of Geology, studies rock layers and layering ( stratification) The law was first proposed in the 17th century by the Danish scientist Nicolas Steno. As a means of recording the passage of Time, the 17th Century was that Century which lasted from 1601 - 1700 in the Gregorian calendar Nicolas Steno ( Danish: Niels Stensen; Latinized to Nicolaus Stenonis) ( January 10, 1638 - November 25,

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Development of the Law of Superposition

Assuming that all rocks and minerals had once been fluid, Steno reasoned that rock strata were formed when particles in a fluid such as water fell to the bottom. This process would leave horizontal layers. Thus Steno's principle of original horizontality states that rock layers form in the horizontal position, and any deviations from this horizontal position are due to the rocks being disturbed later. The Principle of Original Horizontality was proposed by the Danish geological pioneer Nicholas Steno (1638-1686

There are exceptions to this case, because sediments may be deposited on slopes or gradients. These may be steep, locally, and can be up to several degrees. Nevertheless, the principle is essentially true.

Steno stated another, more general principle in this way:

If a solid body is enclosed on all sides by another solid body, of the two bodies that one first became hard which, in the mutual contact, expresses on its own surface the properties of the other surface.

In other words: a solid object will cause any solids that form around it later to conform to its own shape.

Steno was able to show by this reasoning that fossils and crystals must have solidified before the host rock that contains them was formed. If a "tongue stone" had grown within a rock, it would have been distorted by the surrounding rock, in much the same way that a tree root is distorted by growing into a crack in the earth. Instead, the "tongue stone" must have been buried in soft sediments which hardened later. Veins (mineral-filled cracks) and many crystals, on the other hand, must have formed after the surrounding rock was a solid, because they often did show irregularities of form caused by having to conform to the surrounding solid rock. In Geology, a vein is a finite volume within a rock, having a distinct shape filled with Crystals of one or more Minerals which were precipitated

Finally, in the case of strata, layers on top of a set of strata conform to the shape of lower layers. . . and therefore, in a set of strata, the youngest layers must be those of the top layer, and the oldest must lie on the bottom. This is because the youngest layer was deposited after the oldest layers, which determines their place in the layers. Since the oldest was deposited first it is on the bottom and visa versa.

From Steno's observation that rock strata form when particles fall out of suspension in a fluid, it then follows that the youngest stratum is on the top of a sequence. In Chemistry, A suspension is a Heterogenous fluid containing Solid particles that are sufficiently large for Sedimentation. However, this principle also applies to other types of rocks that do not form with water, such as volcanic rocks which spread on older flows, by flow banding. Volcanic rock is an Igneous rock of volcanic origin Texture Volcanic rocks are usually fine-grained or Aphanitic to glassy in Flow banding is a geological term to describe bands or layers that can sometimes be seen in rock that formed from the substance molten rock or magma

Steno realized that other geological processes could create apparent exceptions to his laws of superposition and horizontality . He reasoned that the formation of caves might remove part of a lower layer, and that the collapse of a cave might transport large pieces of an upper layer downwards. He recognized that rocks might be uplifted by subterranean forces. Geologists now recognize that tilting, folding, and faulting may also complicate the analysis of a stratigraphic sequence. See also Folding The term fold is used in Geology when one or a stack of originally flat and planar surfaces such as Sedimentary In Geology a fault, or fault line, is a planar rock fracture which shows evidence of relative movement Molten rock may force its way through surrounding rocks and may sometimes squeeze between older rock layers, also forming an exception to Steno's law. Magma (Plurals magmas and magmata) is molten rock that sometimes forms beneath the surface of the Earth (or any other Terrestrial planet However, such anomalies leave physical evidence in the disturbed rocks; for example, faulted rock layers may be cracked, broken, or metamorphosed along the fault lines. Metamorphism can be defined as the solid state recrystallisation of pre-existing rocks due to changes in heat and/or pressure and/or introduction of fluids i

Steno's law is a statement of relative time, not absolute time: two rock layers, in principle, could form millions of years apart, or days apart.

Application of the law of superposition

Steno himself saw no difficulty in attributing the formation of most rocks to the flood mentioned in the Bible. The story of a Great Flood (also known as the Deluge) sent by a Deity or deities to destroy Civilization as an act of Divine retribution is a However, he noticed that, of the two major rock types in the Apennine Mountains near Florence, Italy, the lower layers had no fossils, while the upper ones were rich in fossils. FOSSIL is a standard protocol for allowing serial communication for Telecommunications programs under the DOS Operating system. He suggested that the upper layers had formed in the flood, after the creation of life, while the lower ones had formed before life had existed. This was the first use of geology to try to distinguish different time periods in the Earth's history – an approach that would develop spectacularly in the work of later scientists. The history of Earth covers approximately 46 billion years (4567000000 years from Earth ’s formation out of the Solar nebula to the present

The Law of Superposition is widely used in creation science to refute geological scientific arguments on the age of the Earth, especially by reference to catastrophism forming turbidites (considered to be evidence of the Great Biblical Flood), which often show exceptions to simplistic applications of the Law of Superposition, specifically the typical conception of a fining up sequence. Creation science or scientific creationism is a movement within Creationism which attempts to use scientific means to disprove the accepted scientific theories on Modern geologists and Geophysicists consider the age of Earth to be around 4 Catastrophism is the idea that Earth has been affected in the distant past by sudden short-lived violent events that were sometimes worldwide in scope Turbidite Geological formations have their origins in Turbidity current deposits, which are deposits from a form of underwater Avalanche that However, Steno did not recognise fining up sequences, and the Law of Superposition has, (as all scientific laws have), been modified to take into account modern conceptions and increased knowledge of the natural world.

Thrust faults were also unknown to Steno and his contemporaries and were not described until the late 19th Century and early 20th century by Peach and Horne at Knockan Crag, Scotland, on the Moine Thrust Fault. A thrust fault is a type of fault, or break in the Earth's crust with resulting movement of each side against the other in which a lower stratigraphic position is pushed up Knockan Crag is a line of cliffs in Assynt, Scotland 21 kilometres (13 miles north of Ullapool. Scotland ( Gaelic: Alba) is a Country in northwest Europethat occupies the northern third of the island of Great Britain. The Moine Thrust Belt is a linear geological feature in the Scottish Highlands which runs from Loch Eriboll on the north coast 190 km south-west to the Sleat peninsula Thrust faults can cause confusion with the Law of Superposition because they occur parallel to bedding and can be difficult to detect, thus creating situations where inexplicably, older strata can overlay younger. Creation science often uses examples of thrust-faulted stratigraphic sections to disprove the ubiquitous applicability of the Law of Superposition.

One further interesting argument proposed by creation scientists is the unconformable chronostratigraphy and repeated chronostratigraphic sections of the Arctic ice sheet and glaciers of Iceland as evidence of catastrophism and violation of Steno's Law of Superposition. Iceland, officially the Republic of Iceland ( ( Ísland or Lýðveldið Ísland ( Such features may, in fact, be a thrust fault hosted within the glacial pile. This is of great importance to stratigraphic dating, which assumes that the law of superposition holds true and that an object cannot be older than the materials of which it is composed.

When combined with the related principle of faunal succession, the law of superposition provides a very powerful tool for dating rocks and strata. The principle of faunal succession is based on the observation that sedimentary rock strata contain Fossilised flora and fauna, and that these In Geology, rock is a naturally occurring aggregate of Minerals and/or Mineraloids The Earth's outer solid layer the ‘ Lithosphere In Geology and related fields a stratum (plural strata) is a layer of rock or Soil with internally consistent characteristics that distinguishes

Superposition as modified by archaeological considerations

Superposition in archaeology and especially in stratification use during excavation 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. The archaeological record is a term used in Archaeology to denote all archaeological evidence, including the physical remains of past human activities which Archaeologists Some archaeological strata (often termed as contexts or layers) are created by undercutting previous strata. In Archaeology, not only the context (physical location of a discovery is a significant fact but the formation of the context is as well An example would be that the silt backfill 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 archaeology requires a degree of interpretation to correctly identify chronological sequences and in this sense superposition in archaeology is more dynamic and multi- dimensional. Archaeology, archeology, or archæology (from Greek grc ἀρχαιολογία archaiologia – grc ἀρχαῖος archaīos The archaeological sequence or sequence for short on a specific Archaeological site can be defined on two levels of rigour

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