Section 1 – Inside the Earth Plate Tectonics Section 1 – Inside the Earth

-Three main layers: 1. crust 2. mantle 3. core

Center of Earth -Temperature: starts cold warmer hot in center -Pressure: deeper you go greater pressure -caused by weight of rocks

The Crust -outer layer of rock 5-100 km thick -thinnest under ocean -thickest under mountains Made mainly of oxygen, silicon, aluminum

-underneath ocean Much denser minerals than continental crust Rocks contain smaller crystals (basalt) -crust on land lighter, less dense Rocks contain larger crystals (granite) The Crust (cont.) Oceanic Crust Continental Crust

The Mantle Lithosphere -layer of hot rock -between crust and core -rigid layer of crust and upper mantle -averages 15-30 km thick

Asthenosphere -soft layer of lower mantle below lithosphere -can bend like plastic -material flows slowly Pieces of the lithosphere (tectonic plates) move on the asthenosphere. -250 km thick

The Core -Outer core: -Inner core: molten metal (iron & nickel) behaves like thick liquid dense ball of solid metal such high pressure, can’t become liquid 6,380 km

Tectonic Plates Pieces of lithosphere that move around on top of the asthenosphere. Fit together like jigsaw Consists of upper mantle, continental and/or oceanic crust J Tuzo Wilson

How does scientists know so much about the depths of Earth without actually going?

Indirect Evidence: What’s inside Earth? -can’t dig to center -closest is a mine 3.8 km deep

Seismic Waves to study interior Vibrations caused by earthquakes Travel at different speeds through Earth depending on density and composition of material. Earth’s is made of different layers

Continental Drift

Alfred Wegener Continental Drift -1912, proposed the hypothesis of continental drift. Hypothesis that states that continents once formed a single landmass, broke up, and drifted to their present locations. This single landmass was called Pangaea “All Earth”

Pieces of Evidence to make continental drift hypothesis. -1. continents seemed to fit -2. fossils found on both sides of ocean were similar -3. glacial activity in areas too warm for ice and mountains

Pangaea Existed about 250 mya Split into two continents – Laurasia and Gondwana about 180 mya Split again to make present continents.

Pangaea Laurasia North America Asia Europe Gondwanaland South America Africa Australia Antarctica India

Sea-Floor Spreading

Sea-floor Spreading Harry Hess Tectonic plates move away from each other. Seafloor spreads apart Magma fills in the gap New crust forms and older crusts gets pushed away from Mid ocean ridge (MOR).

mid-ocean ridge (MOR) sonar -chain of submerged mountains in ocean basins Where sea floor spreading takes place -mapped using sonar -bounce sound waves off underwater objects -records echoes of waves

Evidence for Sea-Floor Spreading Magnetic Reversals Earth’s magnetic pole changes Evidence of these reversals along the ocean floor as the crust moves away from the MOR.

Rift Valley As mountains (MOR) build up a rift valley forms between then in the rift zone.

Plate tectonics -pieces of lithosphere are in constant, slow motion -plates driven by convection currents in mantle -plates float on asthenosphere -plates collide, pull apart, or grind -forms features: volcanoes, mountains, trenches, etc… -plates move 1 to 10 cm per year

Plate boundary -a place where tectonic plates touch -three boundaries: transform, divergent, convergent

Convergent boundaries Subduction -plates come together -results in collision oceanic-oceanic Oceanic-continental Subduction occurs Continental-continental Dense oceanic crust sinks below less dense continental crust.

Divergent boundaries Two plates move apart-separate Form mid ocean ridges -also occur on land; forms rift valley

Transform boundaries -crust neither created nor destroyed -plates slide past each other -example; San Andreas fault in Cali. earthquakes

3 types of Convergent boundaries Continental-continental Continental-oceanic Oceanic-Oceanic Makes mountains Makes trenches and volcanoes b/c of subduction Makes under water mountains

Plate Motion Convection Tracking motion hot rock from deep within Earth rises, but cooler rock near surface sinks. Causes lithosphere to move. very slow movement measured in cm/yr global positioning system (gps)

Deforming the Earth’s Crust

Deformation Process that causes a rock to change because of stress

Types of stress Compression Tension folding When an object is squeezed Ex. Convergent Forces act to stretch on object Ex. Divergent Rock layers bend due to stress

Faulting –rock break and slide past eachother Normal Reverse -breaks in crust where rocks slip past each other

Mountain Formation From Convergent boundaries They start as folds and faults Ex. Folded mts Fault block mts. volcanic mts.

Vertical movement in the earth’s crust: Uplift rising of regions of the earth’s crust to higher elevations. Subsidence the sinking of regions of the earth’s crust to lower elevations.