Law of Superposition - Application of The Law of Superposition

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. 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. 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.

Thrust faults were 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. 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.

When combined with the related principle of faunal succession, the law of superposition provides a very powerful tool for dating rocks and strata.