Plate Tectonics
Joy Nowak
What is plate tectonics?
• A plate is a large, rigid slab of rock.
• The word tectonics comes from the
Greek root “to build”.
• The Earths surface is built of plates.
• The theory of plate tectonics states
that the Earths outermost layer is
fragmented into twelve or more large and
small plates that are moving relative to
one another as they ride atop a hotter,
more mobile material.
Ocean and continental
plates.
• Continental plates are thicker but
less dense.
• Ocean plates are thinner but more
dense.
Earth’s top layers
• Top layer is called the lithoshere, which
contains the crust and the uppermost
part of the rigid mantle.
• Under the lithosphere is the
asthenosphere.
• Asthenosphere consists of of a solid but
low viscosity which can make it flow like
liquid.
• Below the asthenosphere is the deeper
mantle which is more rigid.
Continental drift
• The Earth’s plates are in constant
motion.
• The continents that we know today
were once one super continent known
as Pangaea.
• Over time the continent began to split
slowly creating seven continents.
What drives the plates?
• Harry Hess’ theory is that the
plate-driving force is the slow
movement of hot, softened mantle
that lies below the rigid plates.
• Moving rock beneath the rigid
plates is believed to be moving in
a circular motion.
• The heated rock rises to the
surface, spreads, cools, then sinks
back to down. This cycle is called
convection cell or convective flow
which causes plate movement.
• The plates move very slowly on
the surface, only about two inches
a year on average.
Plate boundaries
• There are three types of plate
boundaries and are characterized
by the way the plates move
relative to each other.
• Each boundary causes different
reactions.
Transform boundaries
• Plates next to each other slide past
each other.
• The plates grind past each other on
transform faults causing earthquakes.
• The San Andreas fault in California is a
transform boundary that has caused
many earthquakes.
Convergent boundaries
• Two plates slide towards each other
causing either a subduction zone or a
continental collision.
• A subduction zone is when one plate
moves underneath the other which can
cause Earthquakes, tsunamis, and
volcanic activity.
• Continental collision causes the plates
to hit each other and raise above the
surface causing mountain ranges.
Divergent boundaries
• Occur where to plates slide apart from
each other.
• The separating plates move apart and
new crust is created by magma pushing
up from the mantle.
• The Mid-Atlantic ridge is a submerged
mountain range from the Artic Ocean to
beyond the southern most tip of Africa.
This was caused by divergent
boundaries.
Sources
• http://en.wikipedia.org/wiki/Plate_tecto
nics
• This Dynamic Earth: The Story of Plate
Tectonics by W. Jacquelyne Kious and
Robert I. Tilling (online book through
usgs.org)
• http://pubs.usgs.gov/gip/dynamic/unde
rstanding.html#anchor6715825
• http://volcano.und.edu/vwdocs/vwlesso
ns/lessons/Plates/Plates11.html
• http://www.windows.ucar.edu/tour/link
=/teacher_resources/teach_snacktecto
nics.html
• http://www.astronomynotes.com/solars
ys/plates-collide.png