Longest mountain system
Encircles the Earth
Peaks up to 12,000 feet high
New oceanic crust is
made here by magma
erupting from the mantle
Steep sided valley splits the top of
the mid-ocean ridge
...called a rift valley
Bill Nye_Seafloor Spreading Video Clip
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Rift valley is 15–30 miles wide
This is where tectonic plates are moving
apart and where magma erupts to form
new oceanic crust
The Mid-Atlantic Ridge
is splitting Iceland.
The East African Rift Zone
may be the next major
ocean.
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Tectonic plates here are moving apart and
new oceanic crust is created by magma
erupting from the mantle
...like two giant conveyor belts slowly moving
in opposite directions and transporting newly
formed oceanic crust away from the rift valley
seafloor spreading animation
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strange rocks shaped like tooth paste squeezed
from a tube
form only when magma erupts underwater and
quickly hardens
Magma = molten rock, minerals, gases
http://www.pmel.noaa.gov/vents/nemo/explor
er/concepts/pillow_lava.html
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Basalt is volcanic
rock
Rich in iron and
magnetite
Grains of magnetite
behave like little
magnets, aligning
with Earth’s
magnetic field
Magma cools and
“locks in” magnetite
Khan Academy_Magnetic
Reversals
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Earth’s magnetic poles have reversed
themselves many times.
Stripes of rock parallel to mid-ocean ridge
alternate in magnetic polarity.
The stripes match perfectly on both sides of
the ridge.
animation with magnetic reversals
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Rock samples further away from the mid
ocean ridge are older than rocks closer to the
mid ocean ridge.
Newly formed oceanic crust pushes older
crust outward and away from the rift
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Oceanic crust created along the mid-ocean
ridge is destroyed and recycled at a deep
ocean trench
This is where tectonic plates are colliding.
The plate carrying denser oceanic crust is
forced under the other plate and back into
the mantle
Seafloor spreading and subduction recycle
ocean floor about every 200 million years and
move continents around
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Khan Academy." Khan Academy. N.p., n.d. Web. 24 Mar.
2012. <http://www.khanacademy.org/>.
Kious, W. Jacquelyne, and Robert I. Tilling. "USGS Developing
the Theory." This Dynamic Earth: The Story of Plate
Tectonics. USGS Publications Warehouse, n.d. Web. 23
Mar. 2012. http://pubs.usgs.gov/gip/dynamic/dynamic
Thinkfilm Inc. (Producer). (2005). Greatest Discoveries with
Bill Nye: Earth Science. [Full Video]. Available from
http://www.discoveryeducation.com/