Page 112 - Science Course 3 (Book 2)
P. 112
Mo11-L2a: What is Relative-Age Dating?
According to the principle of original horizontality,
most rock-forming materials are deposited in
horizontal layers.
Even if rock layers are tilted from being disturbed
or deformed, all the layers were originally deposited
horizontally.
B
M
Original horizontality
C
Rock layers might title, but they
D were f rst deposited horizontally.
A
H
I G Lateral Continuity
F Layers are deposited in continuous sheets in
all directions until they thin out or hit a barrier.
The principle of lateral continuity says that sediments A river might cut through the layers, but the
are deposited in large, continuous sheets in all lateral order of layers does not change.
directions.
The sheets, or layers, continue until they thin out or
meet a barrier.
A piece of an older rock that becomes part of a new
rock is called an inclusion.
According to the principle of inclusions, if one rock
contains pieces of another rock, the rock containing
the pieces is younger than the pieces.
Geologic principles help scientists determine the
relative order of rock layers.
Superposition
The oldest rock on
the bottom of an
undisturbed
sequence of
sedimentary rocks.
104
