In most families a person’s age fits into his or her generation: Siblings are around the same age as are first cousins. The arid climate means that that the rocks are not covered by vegetation.But in some families, multiple marriages, delayed childbearing, extended childbearing or other variations mixes up generations so that Aunt Julia may be five years younger than her nephew. How do Steno’s laws help geologists to decipher the geological history of a region? In many places, especially the national parks, the formations are fantastic. The principles discussed below are easily seen around the Southwest. Why does just about every geology textbook use the Grand Canyon as the example in the sections on geological history? The Southwestern United States is a fantastic place to see geology.
The unconformity was discovered by James Hutton in the 1700s.Hutton saw that the lower rock layers are very old. There are no layers in between the ancient and recent layers.Early geologists had no way to determine the absolute age of a geological material. What they could do was determine the ages of materials relative to each other.If they didn’t see it form, they couldn’t know if a rock was one hundred years or 100 million years old. Using sensible principles they could say whether one rock was older than another.Hutton determined that the rocks were deposited over time. Hutton knew that deposition and erosion are very slow.
He realized that for both to occur would take an extremely long time.Geologic research and mapping requires the determinations of the ages and composition of rocks.A geologic map or report typically is only a summary of investigations that frequently involve the collecting and processing of hundreds of rock samples, followed by the evaluation and interpretation of data from a variety of analytical techniques.This web page provides an overview of selected geochronology methods used by USGS scientists.New dating methods are invented all the time, however, most have practical limitations.These rocks were then uplifted to become mountains. The relative ages of rocks are important for understanding Earth’s history.