What is a type of relative dating of fossils
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.Another way to date an ash-surrounded rock layer is by identifying the geologic era of the fossils it carries.Life arose on Earth approximately four and one-half billion years ago. Sedimentary rocks form from soil and silt carried and deposited by moving water.
These areas are the easiest to date because volcanic debris can usually be radiometrically dated with a high degree of accuracy.
Layers of volcanic ash are igneous deposits, while layers of rock these deposits surround are usually sedimentary. Igneous intrusions form when magma breaks through a layer of rock from beneath, or lava flows down from above. When igneous intrusion causes newer sedimentary layers to sink into older ones, it's called subsidence.
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.