Volcanic ash layer dating
So in order to date most older fossils, scientists look for layers of igneous rock or volcanic ash above and below the fossil.Scientists date igneous rock using elements that are slow to decay, such as uranium and potassium.Major element chemistry of glass shards was determined with electron microprobe analysis on the younger key bed.
Radioactive atoms are inherently unstable; over time, radioactive "parent atoms" decay into stable "daughter atoms." When molten rock cools, forming what are called igneous rocks, radioactive atoms are trapped inside. By measuring the quantity of unstable atoms left in a rock and comparing it to the quantity of stable daughter atoms in the rock, scientists can estimate the amount of time that has passed since that rock formed.Relatively young deposits can be sometimes dated using tree rings, varved-lake sediments, coral growth patterns, and other methods.Paleontology is the study of life in past geologic periods (fossil plants and animals), incorporating knowledge of an organism's phylogeny, relationships to existing organisms, and correlation to an established chronology of Earth History.Once you have an idea how old an ash layer is in an outcrop, that’s one of the tools you can use to help estimate the age of sedimentary layers as well as the age of fossils that may be present in the sedimentary layers.I wanted to know if volcanic ash deposits found in the geologic record are most useful in correlating the age of rock layers if the volcanic ash was distributed over a large area during a short period of time or large area during a long period of time I was thinking over a long period of time because it helps more with determining a rocks age. dating sediments using volcanic ash layer) is specifically its instantaneity (relatively to geological timescale of course). An example would be the Kawakawa/Oruanui tephra from New Zealand which is a good isochronous marker bed at 26.5 ka, spread over 1500km, but represents probably only a few months of volcanic activity (see e. Manville & Wilson 2006) Important factors vis-à-vis the usefulness of a specific ash layer however are its geographical extent (a volcanic event that will spread an ash layer over a whole basin would be more useful in that it will be used to correlate a large number of sites together) and maybe its volume (you need a minimum amount of material to work with, I'll assume).