PCB-4674 Lecture Notes - Lecture 4: Radiometric Dating, Principle Of Faunal Succession, Relative Dating
Document Summary
There are two ways of telling time: look at a clock and read the time off. Clock timing is a direct quantitative evidence of the age of something. Qualitative dating using evidence that the sample is older or younger than something else whose age is known. Key concept around 1830: processes that have gone on in the past are much like the ones happening in the present. We can infer about past events with reference to the processes that we can see going on now. (uniformitarianism) Principle of superposition: older rocks can usually be presumed to be below younger rocks. This can be reversed when rocks get turned over in geological time. We can see that younger rocks intrude into seams in older ones by volcanic action. When this happens we know that the intrusion is the youngest rock, because it needed the surrounding rock to form the vertical intrusions. (principle of cross-cutting relationships)
