Transcript Relative Age Dating

Important Principles in
Geology
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James Hutton th
Scottish geologist during the 18 century
Considered the father of modern geology
Although at the time people thought the
Earth was a few thousand years old, he
proposed that the Earth was many millions
of years old
He tried to calculate soil accumulating in
the ocean to figure out how much time
had passed since the formation of the
Earth
Uniformitarianism
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Hutton used the term to compare the
present day rock cycle with the past rock
cycle
The idea is that “the present is the key to
the past”
From these comparisons he could interpret
how rock layers (strata) were formed but
not the length of time
He could determine which layer was
younger or older, just by the position of
the strata
This is now known as stratigraphy
Stratigraphy
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Geologists can make predictions by
looking at sedimentary processes
going on today
They realize that you can age certain
layers by comparing the materials
and fossils that it contains
This has become an important tool to
unravel the history of the Earth
Relative Age Dating
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Before absolute dating of rocks was
developed in the 20th century,
geologists had to rely on relative age
dating
Relative dating places rock in order
from oldest to youngest
Geologists use specific principles to
determine the ‘age’ of rocks
Principle of Superposition
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In a sequence of unformed
sedimentary rock, the oldest beds
are on the bottom and the youngest
on the top
Principle of Original Horizontality
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Sediment layers are nearly horizontal
when originally deposited.
Strata that are not horizontal have
been deformed by movements of the
Earth’s crust.
Oldest layer is still the bottom.
Principle of Crosscutting Relations
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Geological features, such as faults
and fractures are younger than the
rocks that they cut.
Principle of Inclusion
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If one rock body contains fragments
of another rock body it must be
younger than the fragments of rock
it contains.
The inclusions are older than the
rocks which contain them
B is older than C
Principle of Faunal Succession
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Groups of fossil plants and animals
occur in the geological record in a
definite order.
A period of geological time can be
recognized by its specific fossils.