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Review Geologic Time-2

This is a photograph of the Painted Desert in Arizona. These layers of rock have not been folded or overturned, so we know that the layer on the bottom is the oldest. This is based on:

  1. The Law of Superposition

    Yes! The Law of Superposition tells us that unless the layers have been disturbed, they will be in order of their age, with the youngest on the top, and the oldest on the bottom.
  2. The Law of Crosscutting

    No. The Law of Crosscutting tells us that a feature (crack, fault, igneous intrusion, etc.) that cuts through a layer of rock is younger than the layer it cuts through. That makes sense, because the layer would have to be there first, before it could be broken by a fault, etc.
  3. The Law of Relativity

    No. There is a theory of relativity, which deals with the basics of physics, not geology. There is no Law of Relativity.
  4. The Law of Thermodynamics

    No. The Law of Thermodynamics deals with energy, not with layers of rock.

Click to see which state standards this question tests, and which of my videos, experiments, and other resources support that topic.


SC.7.E.6.3 Identify current methods for measuring the age of Earth and its parts, including the law of superposition and radioactive dating.


UT.8.III.3.c Explain why some sedimentary rock layers may not always appear with youngest rock on top and older rocks below (i.e., folding, faulting).


4-ESS1-1 Identify evidence from patterns in rock formations and fossils in rock layers to support an explanation for changes in a landscape over time.
Reading the Rocks: The Present is the Key to the Past video, ClosedCaptions
Paleo Cookies video
Evaporites video, learnalong, checked
Igneous Rocks and Bubbles video, free, learnalong, Updated
Sedimentary Rocks video, learnalong
Reading the Rocks: Law of Superposition video
Reading the Rocks: Law of Crosscutting video
What is a Rock? video, learnalong, checked
Homemade Fossil Dig text page
Review Rocks-1 practice
Review Geologic Time-1 practice
Review Rocks-4 practice
Review Geologic Time-2 practice
Review Rocks-5 practice
Review Rocks-6 practice
Review Rocks-8 practice
Review Rocks-9 practice
Review Rocks-7 practice
Review Rocks-10 practice
Review Geologic Time-3 practice