Page 114 - Science Course 3 (Book 2)

Mo11-L2b: How to Determine the Relative Ages of Rocks?

index fossil
Type of Unconf rmities
a fossil representative of a species that existed on
Earth for a short length of time, was abundant, and
inhabited many locations.
Disconformity

Younger sedimentary layers are deposited on
top of older, horizontal sedimentary layers that
have been eroded.

Younger
sedimentary rock

Older
sedimentary rock
Let’s Begin

Unconformities Angular Unconformity

An unconformity is a surface where rock has eroded Sedimentary layers are deposited on top of tilted
away, producing a break, or gap, in the rock record. or folded sedimentary layers that have been
eroded.
Younger rocks have been deposited on a layer of
eroded rocks where. Younger
sedimentary rock
12 Fault
11 11
10 10
9 Unconformities 9
8 8
7 7
6
A 5 3 Older
4 2
3 1 sedimentary rock
B 2
1

An unconformity does not represent a gap in the rock; it
represents a gap in time.

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