Transcript Plate Tectonics

Plate Tectonics
•Relative Dating and Rock Layers
http://www.youtube.com/watch?v=_mcC8kFacrk
Earth’s History
How old is our Universe?
13.7 billion years old
How old is Earth?
4.6 billion years old
Earth was once made of molten
lava and magma, eventually
cooling to form igneous rock
Weathering,
Erosion,
Compaction,
Cementation,
Heat, and
Pressure
eventually formed
the rocks that
cover our Earth’s
surface.
What we know about Earth’s history
comes from studying its rocks, rock
formations, rock layers, and even the
rocks from outer space
Meteorites
• All meteorites formed
about the same time
that Earth formed, so
studying them helps
us study Earth.
• Meteorites have not
been affected by
erosion, weathering
or other forces the
way Earth’s rocks
have.
Studying Earth’s Rocks
Rock Layers
• Which book was
placed here first?
• The bottom one!
• When rocks form,
the oldest ones are
usually found
beneath younger
rocks
http://www.youtube.com/watch?v=9Df4CtlZ0AQ
Fossils
• Most fossils are found in
Sedimentary rock layers
• Why?
– Heat, pressure, and
melting would
probably destroy
fossils during the
formation of Igneous
and Metamorphic
rocks
• Sedimentary
rocks, and the
fossils they
trap, are often
found in
layers, oldest
rocks are
found on the
bottom.
http://www.prehistoricplanet.com/news
/index.php?id=48
• Digging through
the layers of
rocks, helps us
understand
more about the
history of Earth.
• The Grand
Canyon (Arizona)
was carved by the
Colorado river,
exposing millions
of years worth of
rock layers.
Sometimes, the rock layers aren’t
always horizontal…
And sometimes ocean fossils are
found high in the mountains…
Why?
• Turns out, our
Earth’s surface
is constantly
shifting,
changing, and
eroding.
• And the layers
get pushed
around.
• Only in the last
200 years, have
we begun to
understand the
structure,
formation and
history of our
Earth.
I wonder
what’s inside
Earth?
Relative Age of Rocks
• To figure out the ages of rocks and their
fossils, geologists rely on a few rules…
Law of Superposition
• In any undisturbed
rock, the oldest
layer is at the
bottom and the
youngest layer is at
the top.
The Cross-Cutting Law
• Any feature that cuts across a body of rock
is younger than the body of sediment or
rock it cuts across.
The Law of Inclusions
• If one rock layer contains fragments
(inclusions) of another rock layer, it must
be younger than the fragments of rocks it
contains.
Younger
Oldest
Youngest