Scientists can use certain types of fossils referred to as index fossils to assist in relative dating via correlation.
Your goal is to study the smooth, parallel layers of rock to learn how the land built up over geologic time.
Now imagine that you come upon a formation like this: What do you think of it? How can you make any conclusions about rock layers that make such a crazy arrangement?
On the other hand, the sedimentary rock (as I know) usually provide the time of formation by age range of fossil e.g. Is there any method to make it more specific like the crystalline one?
Radioactive dating is a method of dating rocks and minerals using radioactive isotopes.
Geologists establish the age of rocks in two ways: numerical dating and relative dating.
Numerical dating determines the actual ages of rocks through the study of radioactive decay.
In example B, the shale is older than the igneous intrusion that cuts through it, but younger than the lava flow beneath it.
The ages of fossils within a sequence of sedimentary rocks can be determined using a combination of both relative and absolute dating, as shown in the diagram below.
Absolute dating is necessary for knowing specific time e.g.
by isotope K/Ar in mica, especially in the crystalline rock: igneous and metamorphic rock.
Free 5-day trial Discover how geologists study the layers in sedimentary rock to establish relative age.