EARTH SCIENCE
PAGES 202-205
THE THEORY OF PLATE TECTONICS
PLATE TECTONICS IS THE THEORY THAT THE EARTH’S LITHOSPHERE IS
DIVIDED INTO TECTONIC PLATES THAT MOVE AROUND ON TOP OF
THE ASTHENOSPHERE.
I. TECTONIC PLATE BOUNDARIES
A. A BOUNDARY IS A PLACE WHERE TECTONIC PLATES TOUCH.
B. THESE BOUNDARIES ARE DIVIDED INTO THREE TYPES:
1) CONVERGENT
2) DIVERGENT
3) TRANSFORM (STRIKE-SLIP)
C. THE TYPE OF BOUNDARY DEPENDS ON HOW THE TECTONIC
PLATES MOVE RELATIVE TO ONE ANOTHER…THEY CAN COLLIDE,
SEPARATE, OR SLIDE PAST EACH OTHER.
D. EARTHQUAKES CAN OCCUR AT ALL
THREE TYPES OF PLATE BOUNDARIES.
1. WHEN TWO TECTONIC PLATES COLLIDE…THE BOUNDARY IS
CALLED A CONVERGENT BOUNDARY…THERE ARE THREE TYPES:
CONTINENTAL-CONTINENTAL--- CONTINENTAL-OCEANIC ---OCEANIC-OCEANIC
2. WHEN TWO TECTONIC PLATES SEPARATE…THE BOUNDARY IS
CALLED A DIVERGENT BOUNDARY…NEW SEA FLOOR FORMS
AT DIVERGENT BOUNDARIES…
MID-OCEANIC RIDGES ARE THE MOST COMMON TYPE OF
DIVERGENT BOUNDARY
3. WHEN TWO PLATES SLIDE PAST EACH OTHER HORIZONTALLY…
IT’S CALLED A TRANSFORM BOUNDARY (STRIKE-SLIP)…THE SAN
ANDREAS FAULT IN CALIFORNIA IS A GOOD EXAMPLE.(THIS IS THE
PLACE WHERE THE PACIFIC AND NORTH AMERICAN PLATES ARE
SLIDING PAST EACH OTHER.)
II. POSSIBLE CAUSES OF TECTONIC PLATE MOTION
A. WHAT CAUSES THE MOTION OF TECTONIC PLATES?
1. REMEMBER THAT THE SOLID ROCK OF THE ASTHENOSPHERE
FLOWS VERY SLOWLY???
2. THIS MOVEMENT OCCURS BECAUSE OF CHANGES IN
DENSITY WITHIN THE ASTHENOSPHERE.
3. THESE DENSITY CHANGES ARE CAUSED BY THE OUTWARD
FLOW OF THERMAL ENERGY FROM DEEP WITHIN THE EARTH.
4. WHEN ROCK IS HEATED, IT EXPANDS, BECOMES LESS DENSE
AND TENDS TO RISE TO THE SURFACE OF THE EARTH.
5. AS THE ROCK GETS NEAR THE SURFACE, THE ROCK COOLS,
BECOMES MORE DENSE, AND TENDS TO SINK.
THREE POSSIBLE DRIVING FORCES OF PLATE
TECTONICS
1. RIDGE PUSH THE OCEANIC LITHOSPHERE SLIDES DOWNHILL
UNDER THE FORCE OF GRAVITY.
2. CONVECTION CAUSES THE OCEANIC LITHOSPHERE TO MOVE
SIDEWAYS AND AWAY FROM THE MID-OCEANIC RIDGE.
3. SLAB PULL THE EDGE OF THE TECTONIC PLATE THAT CONTAINS
OCEANIC LITHOSPHERE SINKS AND PULLS THE REST OF THE
TECTONIC PLATE WITH IT IN A PROCESS CALLED SLAB PULL
III TRACKING TECTONIC PLATE MOTION
A. HOW FAST DO TECTONIC PLATES MOVE?
1. IT DEPENDS ON MANY FACTORS
*THE TYPE AND SHAPE OF TECTONIC PLATES
* THE WAY THAT THE TECTONIC PLATE INTERACTS
WITH THE TECTONIC PLATES AROUND IT.
B. TECTONIC PLATES MOVEMENTS ARE SO SLOW AND GRADUAL
THAT YOU CAN’T SEE OR FEEL THEM—THE MOVEMENT IS
MEASURED IN CENTIMETERS PER YEAR.
C. THE GLOBAL POSITIONING SYSTEM
1. GPS IS USED TO MEASURE THE RATE OF TECTONIC PLATE
MOVEMENT.
2. RADIO SIGNALS ARE CONTINUOUSLY BEAMED FROM
SATELLITES TO THE GPS GROUND STATIONS, WHICH RECORD
THE EXACT DISTANCE BETWEEN THE TWO…OVER TIME, THESE
DISTANCES CHANGE SLIGHTLY…SCIENTISTS CAN MEASURE
THE SPEED AT WHICH EACH TECTONIC PLATE MOVES.
SUMMARY
***BOUNDARIES BETWEEN TECTONIC PLATES ARE CLASSIFIED AS CONVERGENT, DIVERGENT OR
TRANSFORM.
***RIDGE PUSH, CONVECTION, AND SLAB PULL ARE THREE POSSIBLE DRIVING FORCES OF PLATE
TECTONICS.
***SCIENTISTS USE DATA FROM A SYSTEM OF SATELLITES CALLED THE GLOBAL POSITIONING
SYSTEM TO MEASURE THE RATE OF MOTION OF TECTONIC PLATES.