unconformity's where deposition stopped and erosion removed the previously deposited material.Distinctive features such as index fossils can aid in matching, or correlating, rocks and formations from several incomplete areas to create a more complete geologic record for relative dating.THAT was a discrete instant in time geologically since the explosion occurred and the ash fall lasted for years not hundreds or millions So we can identify that layer of ash in the rock record and say..happened in such and such time.
Stratigraphy is the most basic concept used in relative dating and is based on Superposition, which is defined as; each bed in a sequence of sedimentary rocks is younger than the bed below it and older than the bed above it.
This law follows two basic assumptions: beds were originally deposited near horizontal, and the beds were not overturned after their deposition.
Radiometric dating was developed later than relative dating, and requires advanced technology.
Radiometric dating methods rely on the principles of radioactive decay, and this works by measuring the decay of certain radioactive isotopes within tested samples.
Some rock-forming minerals contain naturally occurring radioactive isotopes with very long half-lives unaffected by chemical or physical conditions that exist after the rock is formed.