Download Convection in the Mantle and The Theory of Plate Tectonics

Convection in the Mantle
and
The Theory of Plate Tectonics
Convection in the Mantle
• Density-mass/volume. The amount of matter in a
given area or volume of that matter.
• Fluid-matter that can flow. Can be solids, liquids, or
gases
• Convection-heat transfer within a fluid.
• Convection current -a current that develops from a
fluid moving from an area of high density to an area
of low density.
How do convection currents form?
• Convection currents occur when fluids heat
unevenly and areas develop that are different
in density
What are examples of
convection currents?
Lava Lamps
Boiling water
Ocean Currents
Air currents in clouds
The Mantle
The Theory of Plate Tectonics
What is the theory of plate tectonics?
• The theory of plate tectonics
explains the formation and
movement of Earth’s plates.
• The lithosphere is broken into
sections called plates.
Plate Boundaries:
• Divergent Boundaries- The place where two
plates (pieces of the lithosphere) move apart.
• Most divergent boundaries occur along a midocean ridge where sea-floor spreading occurs.
What is a mid-ocean ridge?
• It is an undersea mountain chain where new
ocean floor is produced at a divergent
boundary.
Convergent Boundaries:
• The place where two plates come together
(often called a collision).
• When two plates collide, the density of the
plate determines which one comes out on
top.
Convergent Boundaries:
• 2 continental plates collide= formation of
mountains
• 1 oceanic + 1 continental collide= oceanic
sinks beneath the continental plate
(subduction) and forms a trench (a narrow,
deep valley along the ocean floor).
• Subduction- the process by which oceanic
crust sinks beneath a less dense plate.
Subduction Diagram
Transform Boundaries:
• A place where two plates slip past each other,
moving in opposite directions.
• Earthquakes often occur along transform
boundaries, but crust is neither created nor
destroyed.
Diagram of plate movement:
Who is Alfred Wegener?
A German scientist who hypothesized the theory of continental drift.
Why wasn’t Alfred
Wegner’s Theory Accepted?
-Alfred Wegner had a lot of evidence to
support his theory.
-He could not explain how the plates moved.
-Because he could not explain how the plates
moved, scientist did not accept his theory.
Evidence for Plate Tectonics
•
Pangaea- The name of the single landmasss
that broke apart 200 million years ago and
gave shape to today’s continents.
Evidence for a Supercontinent
• Land features: mountain ranges and coal fields
appear to line up according to the shape of
continents.
• Fossils: from ancient animals appear to link
continents together as well- mesosaurus,
lystrosaurus (freshwater reptiles), glossopteris
(plant).
• Climate: temperature changes at specific locations
show that continents may have shifted toward or
away from the equator over time.
Evidence for Plate Tectonics
• Sea-Floor Spreading- the process by which
molten material adds new oceanic crust to the
ocean floor.
• The sea floor spreads apart along both sides
of a mid-ocean ridge (divergent boundary), as
new crust is added.
Sea-Floor Spreading Diagram
How do we know the sea-floor actually
spreads?
• Evidence from molten material- new material
is erupting along mid-ocean ridges.
• Evidence from drilling samples- the age of
rocks have been identified through drilling
samples. Rocks farther from the ridge were
the oldest, the youngest rocks were always in
the center of the ridges.