Transcript Relative Dating

Relative Dating
Relative Dating
Relative Dating is one
of the methods that
geologists use to help
tell geologic time.
It can NOT tell us
exactly how old
something is, but…
It can tell us which is
older and which is
younger (in a given
sample)
The First “Law” of Relative Dating
Uniformitarianism: This
basically states that the
processes that are
occurring today are very
similar to the processes
that have been occurring
since Earth formed (or at
least shortly after the Earth
formed).
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Weathering/Erosion
Deposit of Sediments
Gravity
Etc…
The Second “Law” of Relative Dating
Originally Horizontal or
Superposition: Simply
states that the rocks are
going to be deposited in
horizontal layers, with the
oldest ones at the bottom,
and the youngest ones at
the top.
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Again, Gravity doing its
thing
The Third “Law” of Relative Dating
Cross-Cutting
Relationships: Igneous
rocks (those that form from
the cooling of magma), that
intrude into, or move
through layers of
sedimentary rocks (rocks
that form from the deposit of
sediments), are younger
than the rocks they are
cutting through
The Fourth “Law” of Relative Dating
Unconformity: A
“missing” section or
layer of rocks (usually
caused by erosion of
a layer, or layers, with
new/additional
deposits on top).
Using The “Laws” of Relative
Dating
Let’s Start With An Easy One…
A Little Tougher…
• E—oldest:
superposition, on
bottom
• C—superposition
• B—superposition
• A—superposition
• D—crosscutting
relationship and
inclusions
• F—youngest:
crosscutting
Relationships
A
B
F
C
E
D