Chronology

The existence of earth dates back to 4.6 billion years. The chronological meaning of relative dating involves archaeologists’ discovery of tangible products, which provides a sense of an object’s period. It also relates to other finds, times, and places in the archaeological record which helps to build a better picture of how and when humans thrived in the past.

Archaeologists seek to get physical evidence of geological changes and living organisms and material remains and artefacts of human societies, offering them an important insight.

This relative chronology meaning in history is the science of determining the age of the object in comparison to another without specifying the exact age. In the early 20th century, before the discovery of radiometric dating that provided a means of absolute dating, relative dating was used by archaeologists and geologists to determine the ages of materials. It remains a valuable technique even though it can only determine a series of events.

Methods of relative dating

The use of relative chronological methods helps determine humans, plants, or animals’ environment, diet, health, or migration patterns.

The definition of chronology in history allows objects to be located in a previously established chronology. The methods of relative dating are stated as follows. 

Principle of uniformism

• The principle of uniformism or the Doctrine of uniformity states that the laws and processes of the present day that operate in scientific observation have always been used in the past. It applies to anywhere in the universe. 

• Coined by Whehell and advanced by Hutton in the 18th century, it includes the gradualistic concept “the present is the key to the past ” where geological events occur at the same rate now as they have always done.

Intrusive relationship

• The principle of intrusive relationships involves crosscutting intrusions.

•  When an igneous intrusion cuts across a sedimentary rock formation, it can be determined that the igneous intrusion is younger than the sedimentary rock. 

• The different intrusions include stocks, laccoliths, batholiths, sills, and dikes.

Cross-cutting relationships 

• Geologist Nicholas Steno’s theory of geology states that the geologic feature that cuts another is younger than the two.

• Formation of faults and age of the sequences through which they cut. Faults are younger than the rocks they cut; accordingly, if a fault is found that penetrates some formations but not those on top of it, then the formations that were cut are older than the fault, and the ones that are not cut must be younger than the fault.

• There are six basic types of cross-cutting relationship 

• Structural relationship: fractures are cutting through older rock.

• Intrusional relationship: igneous dike is intruded into pre-existing rocks.

• Stratigraphic relationship: an unconformity cuts across older rock layers or other geological features.

• Sedimentological relationship: where currents have eroded older sediment in a local area.

• Paleontological relationship: animal activity or plant growth produces truncation by penetrating pre-existing sedimentary deposits.

• Geomorphological relationship: where a surficial feature, such as a river, flows through a gap in a ridge of rock. 

Inclusion and components

• This relative chronology meaning principle states that if inclusions are found in a formation, they must be older than the formation that contains them. 

• Works in the case of sedimentary rocks and xenoliths.

Original horizontality

• This principle states that the deposition of sediments occurs in horizontal beds. 

• Modern marine and non-marine sediments support this. 

Superposition 

• The law of superposition of relative chronology states that a sedimentary rock layer in a tectonically undisturbed sequence is younger than the one beneath it and older than the one above it. 

•  The only changes brought in this layer are by animals and plants.

• The sedimentary layers are viewed in a vertical timeline. 

Faunal succession

• The principle stated by William Smith ( before Charles darwin’s theory of evolution ) states that the presence or absence of organisms that exist throughout the world is the same. This provides a relative age of the formations in which they are found.  

• This is rather complex as fossils were not found everywhere at that time. 

Lateral continuity 

• The principle states that the layers of sediments are extended in a lateral direction.

• Lateral continuity can determine the amount and type of sediment. However, this layer becomes thinner as the number of materials decreases. 

Inclusion of igneous rocks

•  Small rocks or melt inclusions found trapped within crystals provide much information.

• The study of melt inclusions has led to chemical analysis techniques. 

• The types of igneous rocks include quartz, feldspar, olivine, and pyroxene. 

Included fragments

• The chronology meaning of this law states that clasts in a rock are older than the rock itself.

• Examples include xenolith and derived fossils. 

Conclusion 

Relative chronology, meaning in history, has several methods to determine the events of the solar system objects and is used by scientists to study developing planetary bodies. The study of craters and other features of planets helps us to learn more about the earth. Moreover, the age of rocks and meteorites brought back from outer space is determined using the radioactive age dating method. This study, known as planetology, impacts how global climate change affects us here on earth and what could happen to earth in extreme cases.