Branch of geology that studies rock layers, beds, or strata (singular: stratum).
Stratigraphy
In the 17th century, a Catholic priest formulated the guiding principles of stratigraphy.
Nicolaus Steno
If the sequence is undisturbed, the layers on the bottom are the oldest, while the layers above are younger.
Law of Superposition
Each stratum extends laterally until it encounters a barrier or obstacle.
Law of Lateral Continuity
Strata are deposited horizontally.
Law of Original Horizontality
If a geologic body (like an intrusion) or discontinuity (like a fault) cuts across strata, it must be younger than the strata it cuts.
Law of Cross-cutting Relationships
An igneous rock body that forms when magma cuts through sedimentary layers and solidifies before it reaches the surface.
Intrusion
Sedimentary strata may contain fossils of plants and animals in a definite and invariable sequence.
Principle of Faunal Succession
What is Principle of Faunal Succession?
William Smith introduced another essential principle of stratigraphy.
In the 19th century, an English geologist applied these principles and produced the first geological map of Britain. Since then, he has been regarded as the Father of English Geology.
William Smith
Sometimes, different processes can lead to a gap in a rock sequence called an unconformity. A hiatus is the “missing time” represented by the unconformity in a rock sequence.
There are three types of unconformities:
These principles and unconformities can be used to identify the age of strata in relation to other strata in a method called relative dating. However, this method cannot identify a stratum’s specific or absolute age.
Angular unconformity: strata are disturbed by forces that cause folding, tilting, and/or faulting, they no longer appear horizontal.
Nonconformity: sedimentary strata are deposited on top of igneous or metamorphic rock bodies.
Disconformity: missing stratum or strata in the sequence, usually due to a period of non-deposition or erosion.
Determining the absolute age of a layer requires certain techniques collectively known as?
Absolute dating
One of the best ways to date the numerical age of a rock is to use an absolute dating method called?
Radioisotopic dating or radiometric dating
Are atoms of an element with different numbers of neutrons.
Isotopes
Radioactive isotopes are unstable (parent isotopes) and lose subatomic particles or energy over time in a process called?
Radioactive decay
Eventually, the parent isotope’s configuration reaches a more stable configuration and becomes a daughter isotope. The half-life of a radioactive isotope refers to the time it takes for half of the atoms in a substance to decay.
Essential to stratigraphy and serve as a doorway to know more about prehistoric life.
Fossils
Major catastrophes shaped Earth’s natural landscapes.
Catastrophism
Continuous natural processes seen today shaped Earth’s