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
• Continental plates are thicker but
• Ocean plates are thinner but more
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 consists of of a solid but
low viscosity which can make it flow like
• Below the asthenosphere is the deeper
mantle which is more rigid.
• The Earth’s plates are in constant
• The continents that we know today
were once one super continent known
• 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.
• There are three types of plate
boundaries and are characterized
by the way the plates move
relative to each other.
• Each boundary causes different
• Plates next to each other slide past
• The plates grind past each other on
transform faults causing earthquakes.
• The San Andreas fault in California is a
transform boundary that has caused
• Two plates slide towards each other
causing either a subduction zone or a
• A subduction zone is when one plate
moves underneath the other which can
cause Earthquakes, tsunamis, and
• Continental collision causes the plates
to hit each other and raise above the
surface causing mountain ranges.
• Occur where to plates slide apart from
• 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
• This Dynamic Earth: The Story of Plate
Tectonics by W. Jacquelyne Kious and
Robert I. Tilling (online book through