Time change of radioactive dating
Biostratigraphy: One of the first and most basic scientific dating methods is also one of the easiest to understand.Layers of rock build one atop another — find a fossil or artifact in one layer, and you can reasonably assume it’s older than anything above it.
Let's say an atom is missing a neutron or has an extra neutron. An atom is still the same element if it is missing an electron. For example, there are a lot of carbon (C) atoms in the Universe. Atomic masses are calculated by figuring out the amounts of each type of atom and isotope there are in the Universe.There is a time when it loses its extra neutrons and becomes C-12.The loss of those neutrons is called radioactive decay. For carbon, the decay happens in a few thousand years (5,730 years).Paleontologists still commonly use biostratigraphy to date fossils, often in combination with paleomagnetism and tephrochronology.A submethod within biostratigraphy is faunal association: Sometimes researchers can determine a rough age for a fossil based on established ages of other fauna from the same layer — especially microfauna, which evolve faster, creating shorter spans in the fossil record for each species.
Before more precise absolute dating tools were possible, researchers used a variety of comparative approaches called relative dating.