Tectonic Plates

Lithosphere – outer part of the Earth’s crust. Composed of solid rock.Asthenosphere - the zone below the lithosphere which is more ‘plastic’ so it is easier to bend and moveRadioactivity is the sourc of heat in the mantle

Layers of Earth

2 Kinds of CrustContinental – less dense, thickerOceanic – more dense, thinner

2 Kinds of MantleUpper – solid, floats on…Lower – plastic (somewhat fluid)–Why?•Earth’s crust and upper mantle “float” on the plastic portion of the mantle. (asthenosphere)

Convection Currents

Movement of hot liquid or gas –Heated – rises–Cools – dropsEarth’s Crust Cracks…–Convection currents in mantle cause

cracking in crust–Thermal Convection cause seafloor

to spread and continents to drift

Divergent

Boundary

Convergent Boundary

Divergent – Ocean to Ocean

New crust formed and pushed up - Mid Oceanic Ridges–Ex. Mid-Atlantic Ridge

Ocean Ridges

Divergent-Continent to Continent Continent spreads, ocean basin may

formPaleontologist noticed that fossils were on different continentsArthur Holmes – First proposed that thermal convection in the mantle causes continental driftEx. Red Sea

Convergent –Ocean to Ocean

Older slips below newerSubducted plate melts–Volcanic islands formedEx. Aleutian islands, Japan

Convergent –Ocean to Continent

Ocean plate goes below continent– SubductionSubducted plate partially meltsTrenches – the deepest parts of the ocean.Volcanic mountains– Ex. Western South America

Aleutian Islands

Islands of Japan

Convergent – Continent to

ContinentSame densities, no subductionCompression, folding, upliftingEx. Himalayas, Alps

Transform faulting:Plates move past each other

Another type of plate movement…

San Andreas FaultSan Andreas Fault

How do you think scientists identified the plate boundaries?What is the “Ring of

Fire?”

Crustal Plates

“Connect the dots” – volcanoes and earthquakes8 major plates

Pangea Theory1912 – Alfred WegenerIdea that continents were once part of one large land mass – theory of continental driftHow did he know?–Continents’ shapes fit together like a

puzzle–Rocks and fossils found on different

continents matched

Early 1960sScientific evidence proves continental drift, plate tectonics, and Pangea theory

Ocean Features Picture 2