Transcript Continental drift and plate tectonics

Continental drift and plate
tectonics
Continental Drift
• Modern scientists consider the age of the
Earth to be around 4.54 billion years
• Over that time it has changed a great deal
•
< Geologic time
scale. Time
subdivisions and
geologic ages in
millions of years
(Ma) are after the
Geological
Society of
America 1999
Geologic Time
Scale (image
from Stoffer,
2006).
Continental Drift
• EON ERA PERIOD EPOCH
• The largest division of geologic time is the
Precambrian era
• It is broken up by significant events in
earths history.
• MESOZOIC
• Cretaceous 144 - 66.4Dinosaurs become
extinct; Rocky Mountains begin forming.
• Jurassic 208 - 144Atlantic Ocean begins
to form between N. America & Africa.
• Triassic 245 - 2081st dinosaurs; North
America begins to separate from Africa.
Continental Drift
Continental Drift
Wegener’s hypothesis was that all the continents were
once joined together in a single landmass.
Continental drift – The idea that the continents slowly
moved over Earth’s surface.
Continental Drift
Evidence: _____Sequences
similar types are found arranged
in the same way.
Evidence:_________
Evidence for Continental Drift
Fossils – any trace of an ancient organism that
has been preserved in rock.
Wegener could not provide a
satisfactory explanation for the force
that pushes or pulls the continents.
Evidence: _______
• Same mountain ranges on different
continents seemed to match
Evidence: Puzzle pieces
• All ____ continents fit together like a
puzzle
…an alternate explanation?
1928: Arthur Holmes suggested fluids rise
toward the crust, spread, and sink again.
1930: Wegner dies, unable to adapt
Holmes’ idea to his theory.
Studying Surface Changes
Constructive forces
shape the surface by
building up
mountains.
Destructive forces are
those that slowly wear
away mountains and,
eventually, every
other feature on the
surface.
The Crust
The crust is a layer
of solid rock that
includes both dry
land and the ocean
floor.
Three main layers make up
Earth’s interior: the crust,
the mantle, and the core.
Each layer has its own
conditions and materials.
The Mantle
Earth’s mantle is made up of rock that is very hot,
but solid. The mantle is divided into layers
based on the physical characteristics of those
layers.
The Core
The core is made mostly of the metals iron and
nickel. It consists of two parts–a liquid outer
core and a solid inner core.
Lithosphere
• Rigid, rocky outer layer of the Earth,
consisting of the crust and the solid
outermost layer of the upper mantle.
• It is divided into 7 major plates
• It extends to a depth of about 60 mi (100
km).
Athenosphere
• Zone of the Earth’s mantle lying beneath
the lithosphere, believed to be much hotter
and more fluid than the lithosphere.
So What caused everything to
move in the first place?
__________ Currents
Heating and cooling of the fluid, changes in
the fluid’s density, and the force of gravity
combine to set convection currents in
motion.
Convection
– heat
transfer by
the
movement
of a heated
fluid
Convection
currents –
the flow
that
transfers
heat within
a fluid
Convection Currents in Earth
Heat from the core and the mantle causes
convection currents in the mantle. This
drives plate movement
Sea-Floor Spreading?
the sea floor spreads apart along both sides of a midocean ridge as new crust is added to the ocean floor.
As a result, the ocean floors move like conveyor belts,
carrying the continents along with them.
Evidence for Sea-Floor Spreading
Several types of evidence supported the theory of
sea-floor spreading: eruptions of molten
material, magnetic stripes in the rock of the
ocean floor, and the ages of the rocks
themselves.
Subduction at Trenches
In a process taking tens of millions of years, part of the ocean
floor sinks back into the mantle through deep-ocean trenches.
Deep-ocean trenches are deep underwater canyons formed
where the oceanic crust bends downward.
Subduction – the process by
which the ocean floor sinks
beneath a deep-ocean trench
and back into the mantle.
Growing an Ocean
Because of sea-floor spreading, the distance
between Europe and North America is
increasing by a few centimeters per year.
How Plates Move
The lithosphere is broken into separate sections called plates.
The theory of plate tectonics explains the formation, movement,
and subduction of Earth’s plates and thus the 7 continents.
Scientific
theory – a
well-tested
concept
that
explains a
wide range
of
observation
s
Faults –
breaks in
Earth’s
crust
where
rocks
have
slipped
past each
other
Plate Boundaries
There are three kinds of plate boundaries:
1. divergent boundaries – valleys and trenches
2. convergent boundaries – mountains and volcanoes
3. transform boundaries. – earthquakes zones
A different type of plate movement occurs along each type of boundary.
Rift valley
– a deep
valley that
forms
along the
divergent
boundary
Plate Boundaries
At the locations where two tectonic plates interact,
a boundary between these plates exist. There
are three types of boundaries that geologist
observe. These boundaries are divergent
boundaries, convergent boundaries, and
transform boundaries.