The most well known method of absolute dating is radiocarbon dating, or C14 dating, although saying that, not many people know just what happens. I will do my best to explain in layman terms. Every organism, human, plant, animal, has carbon isotopes. When this organism dies, the unstable carbon isotopes slowly begin to decay. Now when this material begins to decay it does it in a definite mathematical pattern. This forms “an accurate geological time clock of sorts.”1
Another form of absolute dating is less complicated, it is called dendrochronology. This is to get a date from the rings inside a tree sample. When examining a good sample of wood, one that includes the outermost growth ring, dendrochronology can be extremely accurate and “can give not only the year that a tree was felled but even the season.”2 That said it is sometimes difficult to do. Reason being is that pieces of wood containing a long enough sequence of rings are required, of which are pretty big.
With relative dating, as I have stated before, you need something to compare it to. What better thing to use than the good 'ol planet earth! How? Well, stratigraphy. With this one the archaeologist or paleoanthropologist (those who work with extinct hominids) use the layers of dirt to see just when something was there. I have included an example at the end of this blog what stratigraphy is. The layer on top is the most recent, and as the layers continue down it goes further and further back in time. If you ever have seen a rock with some cool lines on it, those cool lines can tell a story longer than life.
But just knowing that something came before something else does not end with the stratigraphic method. The archaeologist or paleoanthropologist carefully insert a big tube into the earth, pull it out, then, again, carefully open it. Once it is open they can see the different layers and can immediately tell what kind of seasons or weather was going on when certain layers of earth were put down. Another way they use stratigraphy is when excavating.
I am sure you have seen those shows where the archaeologist or paleoanthropologist has little square parts boxed off by wire or thread. Real ones do actually use those. Reason being is that they need to write out in which box they found a certain item, and how deep they found it. That is why when they are digging for something they have to be very careful if they do not know just how deep it is. In these sort of excavations, context is everything. If an artifact is taken out of context, or is removed without writing down where exactly it was found, it becomes useless.
Case in point...archaeologists, anthropologists, paleoanthropologists, most of us, depending one what field of each we are in, date old things.
1: Introduction to Physical Anthropology: Jurmain, Kilgore, Trevathan, with Ciochon
2: Archaeology Trail