Editing Geologic time scale (section)

=== Establishment of primary principles ===
Niels Stensen, more commonly known as Nicolas Steno (1638–1686), is credited with establishing four of the guiding principles of stratigraphy.<ref name="Fischer_20093"/> In ''De solido intra solidum naturaliter contento dissertationis prodromus'' Steno states:<ref name="Steno_1669">{{Cite book |last=Steno |first=Nicolaus |url=https://books.google.com/books?id=xz28AAAAIAAJ |title=Nicolai Stenonis de solido intra solidvm natvraliter contento dissertationis prodromvs ad serenissimvm Ferdinandvm II ... |date=1669 |publisher=W. Junk |language=la}}</ref><ref name="Kardel_2018">{{Citation |last1=Kardel |first1=Troels |date=2018 |url=http://link.springer.com/10.1007/978-3-662-55047-2_38 |work=Nicolaus Steno |pages=763–825 |place=Berlin, Heidelberg |publisher=Springer Berlin Heidelberg |language=en |doi=10.1007/978-3-662-55047-2_38 |isbn=978-3-662-55046-5 |access-date=2022-04-20 |last2=Maquet |first2=Paul|title=2.27 the Prodromus to a Dissertation on a Solid Naturally Contained within a Solid }}</ref>
<blockquote>
* When any given stratum was being formed, all the matter resting on it was fluid and, therefore, when the lowest stratum was being formed, none of the upper strata existed.
* ... strata which are either perpendicular to the horizon or inclined to it were at one time parallel to the horizon.
* When any given stratum was being formed, it was either encompassed at its edges by another solid substance or it covered the whole globe of the earth. Hence, it follows that wherever bared edges of strata are seen, either a continuation of the same strata must be looked for or another solid substance must be found that kept the material of the strata from being dispersed.
* If a body or discontinuity cuts across a stratum, it must have formed after that stratum.
</blockquote>
Respectively, these are the principles of superposition, original horizontality, lateral continuity, and cross-cutting relationships. From this Steno reasoned that strata were laid down in succession and inferred relative time (in Steno's belief, time from [[Creation myth|Creation]]). While Steno's principles were simple and attracted much attention, applying them proved challenging.<ref name="Fischer_20093"/> These basic principles, albeit with improved and more nuanced interpretations, still form the foundational principles of determining the correlation of strata relative to geologic time.

Over the course of the 18th-century geologists realised that:
* Sequences of strata often become eroded, distorted, tilted, or even inverted after deposition
* Strata laid down at the same time in different areas could have entirely different appearances
* The strata of any given area represented only part of Earth's long history