Plate
Tectonics
Some History
• The theory of plate tectonics had its beginnings
in 1915 when Alfred Wegener proposed his
theory of “continental drift”
• He proposed that the continents fit together
like a puzzle
• He was not the first to notice this, but he was
the first to realize that the continents were
once joined together
Fossils
• Paleontologists had also found that
there were fossils of similar species
found on continents that are now
separated by huge distances.
• This seemed to show that the earth’s
crust (lithosphere) was moving
Controversy
• Wegener’s ideas were very controversial
because he didn’t have an explanation for why
or how, just that they moved.
• Although Wegener’s theory was later
disproved, it was one of the first times that
the idea of crustal movement had been
introduced and it laid the groundwork for
modern plate tectonics.
Later Evidence
• In the late 1950’s and early 1960’s, evidence
emerged that suggested convection currents
within the Earth’s asthenosphere could be the
driving force behind the movement of the
plates.
• This theory led to equipment such as
seismometers that showed activity along
distinct belts around the world
Tectonic Plates
• These belts defined the edges of the
tectonic plates
• The lithospheric plates do not randomly
meander about the Earth’s surface, but
are driven by internal forces.
• The mantle is believed to move in
circular motions called convection
currents
Modern Theories
• For many years, most scientists believed that
mantle convection, seafloor spreading, and
magma intrusion at mid-ocean ridges were
the predominant mechanisms that drove plate
motion.
• However recently a new theory about
subduction over mid-ocean ridges (sinking of a
cold, dense, oceanic slab into a subduction
zone) is considered the driving force
Today
• Although scientists know that forces within
Earth drive plate motion, they may never
know the exact details.
• That plates move is indisputable, but how or
why is the challenge
• All of our landforms on earth such as
mountain ranges, seafloor, trenches, ocean
ridges, rift zones, and the volcanic ring of fire
are all the result of plate movements