CONTINENTAL DRIFT,

SEAFLOOR SPREADING,

AND PLATE TECTONICS:

Essential

information

CONTINENTAL DRIFT

• 1912- Alfred Wegener (meteorologist)

• THEORY: modern continents were

once all together – PANGAEA

(1 ocean – Panthalassa)

• Over time, Pangaea broke apart,

and its pieces “drifted”, or slid

across the ocean floor into their

present positions

EVIDENCE OF C. DRIFT:

1. “JIGSAW” SHAPE OF CONTINENTS

- MATCHING EVIDENCE ON DIFFERENT CONTINENTS:

2. SAME ROCK TYPES – DIFF. CONTINENTS

3. MATCHING MOUNTAIN CHAINS – DIFF. CONT.S

4. SAME FOSSILS – DIFF. CONTINENTS

5. PLANT FOSSILS IN POLAR REGIONS

“MISPLACED” FOSSILS:

6. PLANT FOSSILS IN POLAR REGIONS

7. COAL DEPOSITS IN POLAR REGIONS

SAME FOSSILS ON “MATCHING”

CONTINENTS

ROCK OF SAME TYPE AND AGE

ON “MATCHING” CONTINENTS

MATCHING GLACIAL DEPOSITS

ON “MATCHING” CONTINENTS

Somewhat right, somewhat

wrong:

Correct: the continents were once in

different locations, and do “drift” over

time (inches / year)

Incorrect: Wegener stated that the

continents were “blocks” of rock that

“slid” across the ocean floor

WHAT WE KNOW TODAY: THE

STRUCTURE OF THE EARTH

CONTINENTS & OCEAN FLOOR

ARE PART OF THE SAME LAYER

OF THE EARTH

HOW DID WE COME TO

KNOW THIS?

SONAR TECHNOLOGY:

DISCOVERED THE MID-ATLANTIC

RIDGE

( FAILED TO FIND ANY BOUNDARY OF MOVEMENT BETWEEN CONTINENTS &

THE SEAFLOOR)

THE MID ATLANTIC RIDGE

THE MID ATLANTIC RIDGE

How “they” found it:

IMAGES OF THE OCEAN FLOOR

• SONAR IMAGES OF

OCEAN FLOOR ( WW II )

• REVEALS RIDGE / RIFT

SYSTEM

• MAGNETIC SURVEY OF

THE OCEAN FLOOR

REVEALS REPEATING

ROCK PATTERNS (click for

animation)

Magnetic data revealed that new rock

was pushing old rock away from the rift –

the process of SEAFLOOR SPREADING: click diagram for seafloor spreading animation (middle of page)

CONTINENTS & THE OCEAN FLOOR ARE PART OF

LITHOSPHERIC PLATES, AND MOVE TOGETHER ON

TOP OF THE ASTHENOSPHERE

CONT. CRUST CONT. CRUST

OCEAN

CRUST

OCEAN

CRUST

UPPER MANTLE UPPER MANTLE

CONVECTION CURRENTS CONVECTION CURRENTS

ASTHENOSPHERE ( MAGMA )

PLATE MOTION PLATE MOTION

LITHO-

SPHERIC PLATE

THE LITHOSPHERE • IS THE MOVING OUTER “SHELL” OF

THE EARTH

• CONSISTS OF THE CRUST AND UPPER

MANTLE (solid, held together by

pressure/friction)

• THE EARTH’S SURFACE CONSISTS OF

12+ LITHOSPHERIC PLATES

• PLATES MOVE INDEPENTDENTLY OF

EACH OTHER ( only inches / year )

HOW DO PLATES MOVE? • THEY’RE LESS DENSE THAN THE

ASTHENOSPHERE, SO THEY FLOAT ON TOP OF IT

• ASTHENOSPHERE IS FLUID – ALLOWS LITHOSPHERE. TO “SLIDE” OVER IT

• THE FORCE OF CONVECTION CURRENTS (flowing rivers of hotter magma) STRIKING THE BOTTOM OF PLATES PUSHES THEM ALONG

• RADIOACTIVE DECAY OF ELEMENTS PROVIDES HEAT THAT “FUELS” CONVECTION CURRENTS

THE MAJOR PLATES

Arrows show direction of plate motion

SO, CONTINENTS “DRIFTED” APART

BECAUSE THE PLATES THAT THEY

WERE A PART OF MOVED OVER TIME –

WEGENER WAS (mostly) RIGHT

MAJOR EARTHQUAKE AND VOLCANO

ZONES EXPLAINED- They occur along

PLATE BOUNDARIES!

THE RING OF FIRE MID ATLANTIC RIDGE