Lesson summarygeologists establish the relative ages of rocks mostly through their understanding of stratigraphic succession.
Can we establish any relative ages between the rock strata or the cause of their formations?
Relative dating cannot establish absolute age, but it can establish whether one rock is older or younger than another.
How to do relative age dating
Geologists use this type of method all the time to establish relative ages of rocks.
Stimulating luminescence: dating method that uses light to measure the amount of radioactivity accumulated by crystals in sand grains or bones since the time they were buried.
Luckily, there are methods, such as the commonly used potassium-argon (k-ar) method, that allows dating of materials that are beyond the limit of radiocarbon dating (table 1).
How do you use relative dating
With only a few geologic principles, we've established the relative dates of all the phenomena we see in the great unconformity.
Archaeology, the arrangement of artifacts or events in a sequence relative to one another but without ties calendrically measured time; the arrangement of artifacts in a typological sequence or seriation.
-argon (k-ar) method: radiometric dating technique that uses the decay of 39k and 40ar in potassium-bearing minerals to determine the absolute age.
How to relative dating
Relative dating puts geologic events in chronological order without requiring that a specific numerical age be assigned to each event.
Thus, the principle of faunal succession makes it possible to determine the relative age of unknown fossils and correlate fossil sites across large discontinuous areas.
They complicate the task of relative dating, because they don't give an accurate picture of what happened in geologic history.
Here is an easy-to understand analogy for your students: relative age dating is like saying that your grandfather is older than you.
Geologists find the cross-cutting principle especially useful for establishing the relative ages of faults and igneous intrusions in sedimentary rocks.
Absolute age dating is like saying you are 15 years old and your grandfather is 77 years old.
If a rock has been partially melted, or otherwise metamorphosed, that causes complications for radiometric (absolute) age dating as well.
Thus, radiocarbon dating is only useful for measuring things that were formed in the relatively recent geologic past.
Determine the relative age of different rocks, geologists start with the assumption that unless something has happened, in a sequence of sedimentary rock layers, the newer rock layers will be on top of older ones.
Dating methods like thermoluminescence, optical stimulating luminescence and electron spin resonance, measure the accumulation of electrons in these imperfections, or "traps," in the crystal structure of the material.
How geologists utilize the laws of relative dating to establish the relative ages of rocks, using the grand canyon as an example.
Dating: radiometric dating technique that uses the decay of 14c in organic material, such as wood or bones, to determine the absolute age of the material.