Plate Tectonics Chapter 6

Earth is made up of materials with different densities. Scientists theorize that Earth began as a spinning mass of rocks and dust about 5 billion years ago.

Explosions from comets and asteroids crashing into its surface, along with the pressure of Earth’s gravity, produced enough heat to melt materials inside Earth. Over time, dense material sank to the center of the Earth and less dense material moved toward the surface, forming Earth’s layers

Composition of the Earth Earth’s Layers CrustMantleCore ContinentalOceanicOuterInner AsthenosphereMesosphere Tree Map

Crust Earth’s crust and the top of the mantle form the Lithosphere (rock sphere) outermost layer of the Earth Cooler rock

Two Types of Crust Continental solid outer layer thicker than oceanic crust (average 30km) less dense than oceanic crust contains older rocks than oceanic Oceanic solid outer layer thinner than continental crust (average 5-8km) more dense than continental crust recycles its oldest rocks at subduction zones

Mantle Extremely thick and contains most of the Earth’s mass. Scientist look on the ocean floor where molten rock from the mantle flows out of active volcanoes Asthenosphere- a layer of hotter, softer rock in the upper mantle.

Core OUTER –melted iron INNER –solid iron –more dense

The lithosphere is made up of many plates.

The lithosphere is split into large and small slabs of rocks called tectonic plates, which fit together like a jigsaw puzzle. Most of the large tectonic plates contain both continental and oceanic crust. The discovery of Earth’s layers and tectonic plates helped scientists answer the mystery of how the continents moved to their present positions.

Continental drift-is the theory that continents can drift apart from one another and have done so in the past. Evidence of continental drift Puzzle-like fit of the continents fossils similar types of rocks same ancient climatic conditions matching glacial grooves Alfred Wegner (German scientist) proposed that all the separate continents of today were once joined in a single landmass that he called Pangaea.

The Theory of Plate Tectonics explains how plates and their continents move.

Scientist combined Wegener’s continental drift hypothesis with information they gained from mapping the sea floor to develop the theory of plate tectonics. Along spreading centers in the sea floor, melted rock rises through cracks, cools, and forms new crust that builds up mid-ocean ridges.

Old crust gets pushed aside, and the sea floor slowly spreads apart. Earth doesn’t get larger, however, because oceanic crust is destroyed along deep-ocean trenches, where the oceanic plates sink into the asthenosphere.

Causes of Tectonic Plate Motion Convection-heating and cooling of the magma in the mantle Ridge Push-process when oceanic plate slides down the lithosphere and asthenosphere boundary Slab pull-denser oceanic crust subducts under the other crust and melts in the mantle

Tectonic Plate Boundaries Tree Map SubductionCollision Subduction

Convergent boundary When two tectonic plates push into one another Continental/Continental collisions: plates buckle and thicken creating mountains Example: Himalaya mountain range Continental/Oceanic collisions: oceanic plates sink under the continental plate creating a subduction zone –Forms deep-ocean trench, volcanic coastal mountains Oceanic/Oceanic collisions: one plate slides under the other one creating a subduction zone –Produces deep-ocean trench, island arcs

Divergent Boundaries When two tectonic plates move away from one another Produces mid-ocean ridges, rift valleys, volcanoes, earthquakes Example: –mid-ocean ridge

Transform Boundaries When two tectonic plates slide past each other in opposite directions. No crust is formed or destroyed. Example: –San Andreas Fault in California

Hotspots can be used to track plate movements. A hot spot is an area of volcanic activity that develops above where magma rises in a plume from the mantle. A hot spot can be used to measure plate movement because it generally stays in one place while the tectonic plate above it keeps moving. Example: Hawaii islands

The plate tectonics theory enables geologist to understand how Earth’s continents and ocean basins formed. It also helps them to predict earthquakes and volcanic activity.