Download Relative Age of Rocks

Relative Age of Rocks
What is relative age?
• The relative age of a rock is its age compared
to the ages of other rocks
• Absolute age is the number of years since the
rock formed
– Found using radioactive dating- ratio of
radioactive and stable isotopes found in rock
• It can be difficult to determine the absolute
age of a rock, so we can use relative age.
Relative age assumes that…
The lower layers are older than the upper layers.
Lower layers would have been deposited first.
YOUNGEST
OLDEST
Relative age assumes that…
An object cannot be older than the materials it
is made up of.
The chocolate chips
had to be made
BEFORE the cookies.
Igneous Rocks
Did they cause metamorphosis in the
surrounding rock?
YES = igneous rock is younger than surrounding
rocks
gcsescience.com
Igneous Rock
Did they cross cut preexisting rock?
YES = they are younger than the rock they cross
cut
Igneous Rock
Were sediments deposited on them after they
formed?
YES = they are older than the sediments.
Photo by Marli Miller, University of Oregon. Used by permission. About.com(fair use policy)
Intrusion of diorite, caused limestone above and below to
become marble.
Principle of Superposition
In sedimentary rocks, the oldest rocks are on the
bottom, and the youngest are on the top.
YOUNGEST
OLDEST
Principle of original horizontality
Sedimentary layers are deposited horizontally.
Layers that are not horizontal have been
deformed by movements of the Earth’s crust.
teacher2.smithtown.k12.ny.us
Principle of faunal succession
Fossils of plants and animals occur in a definite
order, a period of geologic time can be
determined by its fossils.
Index Fossil = fossil of organism that is easily
identified, occurred over a large area, and lived
during a well-defined period of time.
uvm.edu
Principle of crosscutting relations
Geologic features, like faults and igneous
intrusions, are younger than the rocks they cut
through.
earthscienceinmaine.wikispaces.com
Principle of Inclusions
Rock that contains inclusions of preexisting rocks
is younger than the rocks that the inclusions
came from.
http://imnh.isu.edu/exhibits/online/geo_time/geo_principles.htm