List of relative dating methods

Relative dating methods are unable to determine the absolute For a non- exhaustive list of relative dating methods and relative.
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There are two main categories of dating methods in archaeology: Relative dating includes methods that rely on the analysis of comparative data or the context eg, geological, regional, cultural in which the object one wishes to date is found. This approach helps to order events chronologically but it does not provide the absolute age of an object expressed in years.

Relative dating includes different techniques, but the most commonly used are soil stratigraphy analysis and typology. On the other hand, absolute dating includes all methods that provide figures about the real estimated age of archaeological objects or occupations. These methods usually analyze physicochemical transformation phenomena whose rate are known or can be estimated relatively well.

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This is the only type of techniques that can help clarifying the actual age of an object. Absolute dating methods mainly include radiocarbon dating, dendrochronology and thermoluminescence. Stratigraphy Inspired by geology , stratigraphy uses the principle of the superposition of strata which suggests that, in a succession of undisturbed SOILS , the upper horizons are newer than the lower ones.

Generally, each stratum is isolated in a separate chronological unit that incorporates artifacts. However, this method is sometimes limited because the reoccupation of an area may require excavation to establish the foundation of a building, for instance, that goes through older layers. In this case, even if the foundation of the building is found in the same stratigraphic level as the previous occupation, the two events are not contemporary.

Stratigraphic dating remains very reliable when it comes to dating objects or events in undisturbed stratigraphic levels. For example, the oldest human remains known to date in Canada, found at Gore Creek , have been dated using soil stratification. The bones were buried under and are therefore older a layer of ash that resulted from a volcanic eruption dating back to years BP Before Present; "present" indicates c.

Subsequently, radiocarbon dating, an absolute dating technique, was used to date the bones directly and provided a date of BP, showing how useful the combined used of relative and absolute dating can be.

Chronological dating

Moreover, stratigraphic dating is sometimes based on the objects that are found within the soil strata. Indeed, some items whose exact or approximate age is known are called "diagnostic artifacts. Their presence on archaeological sites is used to date the soil layers and the objects and events they are associated with and thus contributes to refine the chronology of sites. Typology Typology is a method that compares reference objects in order to classify them according to their similarity or dissimilarity and link them to a specific context or period.

This technique is frequently used when it is impossible to make use of absolute dating methods; it generally allows archaeologists to identify the period to which a cultural site or object belongs, without specifying the date of occupation. Geologists use this type of method all the time to establish relative ages of rocks. What could a geologist say about that section of rock?

Following the Principle of Original Horizontality, he could say that whatever forces caused the deformation, like an earthquake, must have occurred after the formation of all the rock strata. Since we assume all the layers were originally horizontal, then anything that made them not horizontal had to have happened after the fact.

We follow this same idea, with a few variations, when we talk about cross-cutting relationships in rock. Let's say, in this set of rock strata, that we found a single intrusion of igneous rock punching through the sedimentary layers. We could assume that this igneous intrusion must have happened after the formation of the strata. If it had happened before the layers had formed, then we wouldn't see it punching through all the layers; we would only see it going through the layers that had existed at the time that it happened.

The newer layers would have formed a cap overtop.


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The Principle of Cross-Cutting Relationships states that rock formations that cut across other rocks must be younger than the rocks that they cut across. The same idea applies to fault lines that slide rock layers apart from each other; a fault that cuts across a set of strata must have occurred after the formation of that set. Geologists find the cross-cutting principle especially useful for establishing the relative ages of faults and igneous intrusions in sedimentary rocks.

Relative dating

Sometimes, geologists find strange things inside the strata, like chunks of metamorphic or igneous rock. These items are called inclusions - foreign bodies of rock or mineral enclosed within another rock. Because the sedimentary rock had to have formed around the object for it to be encased within the layers, geologists can establish relative dates between the inclusions and the surrounding rock.


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Inclusions are always older than the sedimentary rock within which they are found. Other times, geologists discover patterns in rock layers that give them confusing information.

There may be a layer missing in the strata, or a set of sedimentary rock on top of metamorphic rock. These interfaces between discontinuous layers of rock are called unconformities. They complicate the task of relative dating, because they don't give an accurate picture of what happened in geologic history. For example, say we have a layer missing from the rock strata. That layer may have eroded away before the next layer was built upon the exposed surface. So, we'll never know what type of rock used to be there or what fossils it may have held. One famous example of an unconformity is the Great Unconformity of the Grand Canyon.

It clearly shows the interface between two types of rock: The sandstones lie horizontally, just as they did when they were originally laid down. But, the shales are all deformed and folded up. The tops of their folds are completely gone where the sandstones have replaced them. What can we make of this giant unconformity? Can we establish any relative ages between the rock strata or the cause of their formations? Well, following the Principle of Cross-Cutting Relationships, we can tell that whatever deformed the shales - probably an earthquake - must have occurred before any of the upper sandstones were deposited.

In fact, we can put together a timeline.

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The shales were deposited first, in a horizontal position, and then there was an earthquake that made them all fold up. Then, the tops were eroded off until the rock was basically flat, and then the sandstones were deposited on top of everything else. With only a few geologic principles, we've established the relative dates of all the phenomena we see in the Great Unconformity. Geologists establish the relative ages of rocks mostly through their understanding of stratigraphic succession. The Principle of Original Horizontality states that all rock layers were originally horizontal.

The Law of Superposition states that younger strata lie on top of older strata. The Principle of Cross-Cutting Relationships states that intrusions and faults that cut across rock are necessarily younger than that rock. Inclusions , or foreign bodies, found inside rock are necessarily older than that rock. And, unconformities show a discontinuity in the strata, which can only be understood by following the principles of stratigraphy.

Geologists utilize all of these laws and principles to establish the relative ages of rocks and the relationships between events that occurred throughout geologic time.

Chronological dating - Wikipedia

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