Transcript Ch. 7 Study Guide - Lindbergh Schools

Convection currents
• The circulation of material caused by differences in temperature and
density
• The rice in the beaker would rise and fall with the water as it heated
up and cooled off.
• Convection Currents happen in the mantle and cause the molten
rock/magma to circulate (rise and fall) which causes the plates to
move
Divergent Boundary
• We moved the graham crackers apart and there was icing (mantle) left in the
middle to “cool” off and become new crust
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When plates move AWAY from each other
Happens where the seafloor spreads (mid-ocean ridge)
New land (crust) forms
Newest land is closest to ridge, oldest land is furthest away from ridge
Convergent Boundary
• Moved the graham crackers back towards each other and some of the
“mantle” (icing) squished or oozed up between the 2 cracker
(mountains)
• Form where 2 plates Collide or Come together
• Both plates are equally dense, so neither subduct (sink) they will both
uplift (mountains)
• Himalayas are an example
Transform Boundary
• We moved the graham crackers past each other causing them to
grind, crunch, it caused tension they crumbled a little
• Forms when 2 plates slide past each other
• Earthquakes are common along these plate boundaries
• An example is the San Andres fault in California
Convergent- Subduction Boundary
• This was our last step when we pushed one cracker under the other.
• Forms when two plates collide. The denser plate (oceanic) will sink
below the more buoyant (floats easier) continental crust.
• Denser plate will subduct
• Occurs when a continental crust meets a oceanic crust.
• Volcanoes happen here at the edge of continent
• An example is Mount. Ranier
Earth’s Magnetism
• The earth (basically) has a giant bar magnet in the middle of it. Because the earths
core is made of rocks (iron-rich minerals) and metals that are magnetic.
• Every few hundred to few thousand years the magnetic poles reverse. This makes the
rock layers magnetic polarity change. So scientists can tell when the polarity was
normal (magnetic north pointing to the north pole and magnetic south pointing the
south pole) and when it was reversed. (the opposite: magnetic north pointing to the
south pole)
This is NORMAL polarity, because a
compass will point towards Geographic
North (north pole) because opposites
attract SO the South Magnetic Pole (in
the geographic north/north pole) will
attract the compass to point North
• This shows that plates are moving because at mid-ocean ridges mantle rock is
coming out and being pushed away from it, so it shows the magnetic polarity
Evidence Plates are Moving
• Sonar
• Continental Drift (Alfred Wegener)
• Seafloor spreading
• Volcanoes and Earthquakes
• Pangaea/fossils around the world- in places they wouldn’t be able to
get to unless the continents were once closer
• Rock clues: similar rock formations/mountain ranges on different
continents (scientists can now tell how and when rock formations
were formed)