Dating fossils accurate average length of dating
However, paleoanthropologists rarely use it to date sites more than several million years old.
rock, soil, and clay produce constant low amounts of background ionizing radiation.
We know layer C was deposited no earlier than 3.0 mya but it couldn't have been deposited less than 2.5 mya because that fossil had went extinct and isn't seen 2.4 mya. If that fossil was the only fossil we found in any of the layers, all we could say is that layer B was deposited between 4.5-1.0 mya and that layer A is younger and layers C-F are older.
However, because we have two fossils, we can narrow our time considerably.
Let's pretend for the sake of simplicity that all the fossils we've found are really well-studied and our dating of them is as accurate as it possibly can be.
Now, we know that layer D cannot be any older than 4.5 mya because the fossil found there didn't exist earlier in time. In layer B, the fossil closest to the top doesn't tell us a whole lot on its own.
Let's say we have a bunch of rock layers and we can't date them (see image below).
In addition, any argon that existed prior to the last time the rock was molten will have been driven off by the intense heat.
As a result, all of the argon-40 in a volcanic rock sample is assumed to date from that time.
When a fossil is sandwiched between two such volcanic deposits, their potassium-argon dates provide a minimum and maximum age.
As a result, there is a changing ratio of carbon-14 to the more atomically stable carbon-12 involves actually counting individual carbon-14 atoms.
This allows the dating of much older and smaller samples but at a far higher cost.