Transcript Plate tectonicsx - School District 27J

PLATE
TECTONICS
BHS Earth & Space Science
EVIDENCE OF
CRUSTAL
MOVEMENT
• The rock layers at Earth’s
surface are constantly in
motion.
• Principle of original
horizontality – all rocks form
in horizontal layers called
strata (singular: stratum).
• But we often see deformed
strata.
• (Oh noes!)
STRATA
EVIDENCE OF
CRUSTAL
MOVEMENT
• There are three types of
deformed rock.
• 1) Folded rock strata
• Lateral forces push together
and deform folded rock
either upwards or
downwards.
• An anticline forms an arch. A
syncline forms a bowl-like
depression.
SYNCLINE
EVIDENCE OF
CRUSTAL
MOVEMENT
• 2) Tilted rock
• Strata tilt angularly upwards
or downwards.
TILTED ROCK
EVIDENCE OF
CRUSTAL
MOVEMENT
• 3) Faulted rock
• A fault is where a large crack
occurs in the rock and the
strata move up or down
along the fault.
• Normal fault
• Hanging fault
TOP: NORMAL
FAULT
BOTTOM:
HANGING OR
REVERSE
FAULT
EVIDENCE OF
CRUSTAL
MOVEMENT
• Location of fossils in
sedimentary rock reveals
that the Earth’s crust is
dynamic, e.g. marine fossils
on Mt. Everest.
• Benchmark elevation
markers are placed all over
the world. Measurements
taken over time reveal that
positions of the markers are
changing.
• Satellite data can show how
fast tectonic plates are
moving.
EVIDENCE OF
CRUSTAL
MOVEMENT
• A geosyncline: a large
shallow ocean basin where
sediments accumulate near
the edges of the continents.
• The weight of the sediments
causes continent to rise
upward.
GEOSYNCLINE
EVIDENCE OF
CRUSTAL
MOVEMENT
• Isostasy: the Earth’s crust is
in a state of equilibrium. The
lighter continents float on
the mantle, and the denser
ocean basins sink into the
mantle.
• If a plate sinks somewhere, a
plate somewhere else must
rise.
• It’s like squeezing a water
balloon.
ISOSTASY
CONTINENTAL
DRIFT
• Alfred Wegener, a
meteorologist, in 1912
formulated a theory called
continental drift that
explained how continents
were connected and drifted
apart.
• He studied fossils from Africa
and South America and
found many of the same
species (indicator species).
DISTRIBUTION
OF THE FERN
GLOSSOPTERIS
CONTINENTAL
DRIFT
• Geologists shrugged and
hypothesized that ancient
land bridges connected the
continents but disappeared
long ago.
• Rock types were also similar
and scars were left on rocks
by glaciers, with the direction
of the scarring matching on
both continents.
CONTINENTAL
DRIFT
• Wegener’s theory was
rejected for two reasons:
• He was a meteorologist, not
a geologist. People can be
protective of their niche.
• He failed to provide the
mechanism for drift – what
could move a continent?
• His theory was dismissed,
and he died in 1930. In 1960,
it turned out he was right.
Oops.
SEAFLOOR
SPREADING
• After WWII, the US military
used sonar technology
(developed to find enemy
submarines) to take a look at
the ocean floor.
• Underwater mapping
revealed mountain ranges
called mid-ocean ridges.
• New crust was being formed
at the center and moving
outward from the ridge.
SEAFLOOR
SPREADING
• Evidence included alternating
bands of magnetic crystals –
and magnetic north and
south reversed periodically.
SEAFLOOR
SPREADING
• Scientists dated rock from
mid-ocean ridges and the
older rocks were farther from
the ridge center and cooled
as they moved outward.
SEAFLOOR
SPREADING
• This indicated large
convection cells within the
Earth’s mantle, and proved
Wegener’s theory right.
THE THEORY
OF PLATE
TECTONICS
• Earth’s surface is composed
of large, moving plates,
floating on semi-liquid
asthenosphere.
• The plates’ edges are called
plate boundaries, and can be
detected by presence of
volcanoes and earthquakes.
• 15 major plates and many
more minor ones. They move
1 to 10cm/yr.
DIVERGENT
PLATE
BOUNDARIES
• Two plates moving away
from each other that create
new crust.
• Divergent boundaries form
mid-ocean ridges
underwater, and rift valleys
on land.
CONVERGENT
PLATE
BOUNDARIES
• When two boundaries
collide: 3 types.
• Continental-Continental:
forms mountains.
• Oceanic-Oceanic: Subduction
forms trenches and volcanic
arcs.
• Oceanic-Continental:
Subduction forms trenches
and volcanic mountain
ranges
TRANSFORM
PLATE
BOUNDARIES
• When two plates slide along
one another (a lateral fault)
• Great tension is built up
along the fault due to
friction, then released as an
earthquake!
– San Andreas fault, CA
– Golden fault, CO
MANTLE
CONVECTION
• Heated material rises,
spreads out, cools, then
sinks.
• The Earth is like a giant lava
lamp. With people and stuff.
• Hot spots: where magma
rises and breaks through
crust.
– Some are along plate
boundaries (mid-ocean
ridges), others are in the
middle of plates.
– Yellowstone, Iceland &
Hawaii
MANTLE
CONVECTION
HOT SPOT
A SPOT WHERE
MAGMA REACHES THE
SURFACE IN THE
CENTRAL PART OF A
PLATE INSTEAD OF
ALONG THE EDGE
WHICH STATE IN THE U.S.A IS
A RESULT OF A HOT SPOT
UNDER A MOVING PLATE?
WHICH NATIONAL PARK IN THE
U.S.A IS A RESULT OF A HOT
SPOT UNDER A MOVING PLATE?
SEVERAL PLATE BOUNDARY FEATURES