Dating of volcanic ash
If you know this rate and you know the proportion of potassium 40 to argon 40 in the surrounding ash, you can estimate the age of the surrounded rock layer. She has published several books, specializing in zoology and animal husbandry.
Libal holds a degree in behavioral science: animal science from Moorpark College, a Bachelor of Arts from Sarah Lawrence College and is a graduate student in cryptozoology. "How to Find the Age of a Layer of Rock That Is Surrounded by Layers of Volcanic Ash" last modified April 25, 2017.
Tuff radiometry usually uses potassium-argon dating. Volcanic debris contains feldspar crystals, full of an isotope called potassium 40.
Potassium 40 decays into argon 40 at a predictable rate over enormous spans of time.
According to the law of superposition, as long as an area remains undeformed by outside forces, the deeper you go down through the layers of rock, the older they are.
So, if you know the ages of the layers in the parent and wall rocks, you can calculate the age of the layers in your subsided area or xenolith by matching them.
When they break and engulf chunks of sedimentary rocks, it's called stoping. The original rock layers around subsidence areas are called wall rocks and the layers that xenoliths came from are called parent rocks.
From the Precambrian to the present, each geologic era is associated with characteristic fossils.
By identifying the species of the fossils, you can calculate the relative age of any rock layer that contains fossils. However, it only gives a rough range of possible ages, since each geologic era spans many millions of years.
Dating the ash layers above and below a sedimentary rock layer to determine its age is called bracketing.
Radiometric dating uses the decay of unstable isotopes -- atoms with specific electrical charges -- to calculate something's age.