01
Lower layers formed first
In an undisturbed sedimentary stack, older layers lie below younger layers. This is superposition.
Earth & space · 26 minutes
A cliff is a stack of events
An undisturbed layer is usually younger than the layer below it. A feature that cuts through a layer must be younger than the layer it cuts.
Keep this question in mindHow can a rock record the past?
01
Notice the problem
Time left clues instead of labels.
Position, cutting relationships, fossils, and atomic ratios each preserve part of the history.
Six events. One cliff.Time left clues instead of labels.
Position, cutting relationships, fossils, and atomic ratios each preserve part of the history.
02
Three things to notice
Look at these three ideas.
Each picture shows one part of the question. You will test the ideas next.
02
A cut happened later
A fault or magma body is younger than every rock layer it crosses.
03
Unstable atoms act as clocks
A radioactive parent isotope changes into a daughter isotope at a measured statistical rate.
03
Your prediction
Which evidence can establish both event order and a numeric age?
Choose what you think will happen. It is fine to be wrong. The experiment will help you find out.
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