Earth is an unusual planet in that it doesn't have very many impact craters -- they've mostly been obliterated by active geology. Potassium on the other hand has a half like of 1. You May Also Like. This technique relies on a unique physicochemical property of certain minerals especially quartz and feldspar that have an imperfect structure and therefore retain radioactive elements in the natural environment. Just like a stack of sedimentary rocks, time is recorded in horizontal layers, with the oldest layer on the bottom, superposed by ever-younger layers, until you get to the most recent stuff on the tippy top.
Look how squished the Moon's history is! This happens at known rates. Anything below the Taupo tephra is earlier than ; anything above it is later.