Geologic Profiles
• The Earth can tells us
its history if we only
look at the clues
– Types of rocks present
– Ages
– Formations present
• Sills
• Dikes
• Faults
Igneous Intrusive rocks
• Form as magma solidifies underground
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Batholith
Dike
Sill
Pipe or Neck
Laccolith or Lopolith
Phacolith: anticline or syncline
• a sill is a tabular pluton
that has intruded between
older layers of
sedimentary rock, beds of
volcanic lava or tuff, or
even along the direction
of foliation in
metamorphic rock.
http://en.wikipedia.org/wiki/Sill_(geology)
• the sill does not cut
across preexisting rocks,
in contrast to dikes, which
do cut across older rocks.
Dikes
• A dike or dyke in geology
is a type of referring to
any geologic body that
cuts discordantly across
• be either intrusive or
sedimentary in origin.
• http://en.wikipedia.org/wik
i/Dike_(geology)
Volcanic Necks
• Volcanic neck
• Igneous intrusion
• How did Devil’s tower
form?
• http://www.unmuseum
.org/devtowergeo.htm
http://en.wikipedia.org/wiki/Devils_Tower_National_Monument
Batholith
• is a large emplacement of
igneous intrusive (also
called plutonic) rock that
forms from cooled
magma deep in the
Earth's crust.
http://en.wikipedia.org/wiki/Batholith
Batholiths are almost
always made mostly of
felsic or intermediate
rock-types, such as
granite, quartz
monzonite, or diorite (see
also granite dome).
http://en.wikipedia.org/wiki/Syncline
Determining Age
• Two Methods
– 1. Relative Age
– 2. Absolute Age
http://en.wikipedia.org/wiki/Fossil
Relative Age: How old is a rock in
comparison to others
• Examine geologic profiles
• Examine fossils present
in the rock
• Index fossil: a fossil of a
plant or animal that was
very common during a
specific time period
• (Who’s on First Activity)
• Law of Superposition
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_________________
A
B A
A
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B
A
A B
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A A
C
A
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AB B A B
Absolute Age: determining approximate
age of rock
Radioactive Dating: can be
used on igneous rocks
and certain fossils
radioactive isotopes
are present when rocks
are made and living
things die
Radioactive isotopes decay
over time and we can
measure the amount left
to determine age
Short clip on C14
http://videos.howstuffworks.com/
hsw/22270-the-earliestimmigrants-carbon-14-datingvideo.htm
Works Cited
• "Copyright 2009 by Andrew Alden,
geology.about.com, reproduced under
educational fair use.“
• Wikipedia