EARTH SCIENCEPAGES 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.