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Home , Lower mantle (Earth)

Layers of the - Students’ Notes

Geology – comes from two Greek roots: ‘geo’ means earth and ‘logos’ means the study of. So is the study of earth. Scientists use seismic waves to study the layers of the Earth.

Earth’s shape is nearly a sphere, with a slight flattening at the poles. The ocean covers 71% of the earth’s surface. Seven major continents make up the rest of the surface. Name the continents: Australia, Asia, Africa, Antarctica, Europe, North America and South America.

I. Four Layers – they get hotter as they go deeper

A. : outermost layer - two types

1. is formed over the continents. The thickest parts are under mountain ranges.

2. is found beneath the ocean floor and is much thinner than the continental crust.

B. : accounts for more than 80% of the volume of Earth. It is divided into zones of different densities. The is less dense and the is more dense.

1. – is made up of the crust and the upper most solid portion of the mantle.

C. Core: is the very center of the earth. It is made up of mostly (Fe) and nickel (Ni). It is divided into two parts: outer core, inner core

1. Outer Core: is molten liquid

2. Inner Core: is solid. This is the hottest layer.

Continental Drift and good resource http://pubs.usgs.gov/gip/dynamic/understanding.html#anchor15039288

I. Continental Drift A. Proposed by Alfred Wegener in 1912 1. Theory that Earth’s continents were once joined in a large landmass that broke apart. The continents drifted to their current locations. (they drift a few centimeters each year) 2. Named the giant landmass Pangaea- Greek word that means “all Earth” 3. Fossils and rock formations found on the different continents support his theory. 4. Theory was not readily accepted because he couldn’t explain how it happened.

II. Plate Tectonics Theory - A. The theory is that the Earth is divided into lithospheric or tectonic plates that move about the Earth (like slabs of ice on a lake) “tekton” is a Greek word that means “to build”. They move at a rate of 1-10 cm per year.

B. Lithosphere - (lithos is Greek root for rock or stone)

1. Outermost layer of Earth’s surface 2. Includes the crust and the rigid portion of the upper mantle 3. Composed of tectonic or lithospheric plates (7 major plates- corresponding w/ the continents and 7 minor plates) 4. Part of the Earth where all geological events take place: earthquakes, volcanoes, , tsunamis, geysers, erosion, and rock formation

III. Convection Current A. Hypothesis to explain how plates move B. – this is the upper part of the mantle that is partially molten in places. Convection current takes place in this layer. C. Hot molten material in the mantle becomes less dense and rises D. Material nearer to Earth’s surface spreads out, cools and becomes denser. Then it sinks below the hotter, less dense material. E. Uneven heating causes material in the mantle to constantly and slowly rise and fall, resulting in convection current. F. As the currents move molten material sideways, large portions of crust (plates) “ride” on top across the Earth’s surface. IV. Plate Boundaries – A. The place where the edges of tectonic plates meet. B. Types of boundaries depend on whether the plates forming them are moving toward each other, separating or sliding past each other. C. Geologic events happen along these different boundaries D. Three Different BoundaryTypes:

i. Convergent Boundary - Forms where plates collide. 3 possibilities:

1. Continental Plate to Continental Plate: the two plates just fold together and keep pushing on each other. Mountains are formed. (example: Himalayas)

2. Continental Plate to Ocean Plate: two plates come together and the oceanic plate slides underneath the continental plate. The lower one starts being melted back into magma. This is called . (example: Andes Mtns.)This molten material, which is under great pressure can escape through weak spots in the Earth’s crust. What can happen? Erupting volcanoes.

3. Ocean Plate to Ocean Plate: two plates come together and one slides under the other (subduction) When this happens in the middle of the ocean, strings of volcanic islands are formed. (example: Hawaii)

ii. Divergent Boundary 1. Forms when 2 plates diverge, or move away from each other. This usually happens on the ocean floor. 2. A space is created where magma comes through, forming new crust. The creation of new ocean floor is called seafloor spreading. 3. They build under mountain ranges (example: Mid-Atlantic Ridge which is longest mountain range in world)

iii. Transform Boundary (lateral boundary) 1. Forms when two plates slide past each other in opposite directions, without creating or destroying crust. 2. Causes earthquakes as boundaries grind against each other. (Example: San Andreas Fault) 3. Called seismic zones 4. Can also create mountains, valleys and volcanoes.

Ring of Fire

Ring shaped belt of volcanic and earthquake activity surrounding the Pacific Ocean. This happens because there are so many plates either converging, diverging, or transforming along the edges of the Pacific Plate. It is usually the dense oceanic crust that is moving under the less dense continental plates.