CONTINENTAL DRIFT, SEAFLOOR SPREADING, AND PLATE TECTONICS · PDF fileSomewhat right, somewhat...
Transcript of CONTINENTAL DRIFT, SEAFLOOR SPREADING, AND PLATE TECTONICS · PDF fileSomewhat right, somewhat...
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
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
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)
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
SO, CONTINENTS “DRIFTED” APART
BECAUSE THE PLATES THAT THEY
WERE A PART OF MOVED OVER TIME –
WEGENER WAS (mostly) RIGHT