Structure of the Earth
(ppt: Plate Tectonics)
Earth is made up of a series of layers the Core, Mantle and Crust. (S1)
Core:
The Core is made up of 2 regions an Inner Core and an Outer Core
Inner Core:
Made up of solid Iron and Nickel
1,200 Km in radius
Temperature around 5,000º C
Outer Core:
Made up of liquid Iron and Nickel Ions
Responsible for Earth’s Magnetic Field
2,250 Km thick
Temperature range: 2,200 – 5,000º C (Increasing with depth)
Mantle:
Made up of Silicon, Oxygen, Iron and Magnesium
Temperature range; 870 - 2,200º C (Increasing with depth)
2,900 Km thick
Mantle material has a high density, plastic-like consistency that flows as a result of
convection currents created by the heat of the core. (S2)
Crust:
Hard outer layer of the Earth.
2 Types: (S3)
Oceanic: (underlies oceans)
Continental: (makes up landmasses)
Oceanic Crust (Sample Basalt)
Made up primarily of Basalt (Dark, Dense Rock)
Average thickness = 8 Km (5 mi)
Continental Crust (Sample Granite)
Made up primarily of Granite
Average thickness = 32 Km (can be up to 72 Km thick under mountain ranges)
Plate Tectonics
The crust is broken into sections called plates. There are around a dozen major and numerous
minor plates. (S4)
Convection currents in the mantle cause the plates to move. (S5)
Plates move 3 ways compared to each other. These three movements are: (S6)
1. Divergence
2. Convergence
3. Transform
When plates separate magma moves up through the gap creating new crustal material and a
ridge. This is most prevalent along the Mid-Atlantic Ridge. The newly formed crust
preserves the Earth’s magnetism at the time the material was formed. This record shows that
the Earth’s magnetism has reversed polarity a number of times in the past.
Divergence (S7)
Mid-Atlantic Ridge (S8)
Fossilized Magnetism (S9 & 10)
Divergence: When they pull away from each other it causes tears in the crustal material
forming a valley called a Rift Valley. Connecticut’s central valley is a rift valley formed when
the North American and African Plates separated. (S 11)
When plates rub and press against each other they cause:
Earthquakes
Volcanoes
Mountain Building
Convergence: When an Oceanic Crust collides with a Continental Crust the Oceanic Crust,
which is denser and thinner, gets pushed down and heats up forming magma that moves up
through cracks in the Continental Crust forming a line of volcanoes, mountains and giving
rise to an Earthquake zone. This is called Subduction. The largest earthquakes occur as a
result of subduction. (S12)
When 2 Continental collide it causes them to buckle and fold upward into mountains. The
plates can become locked together forming one larger plate as happened in the collision that
created the Rocky Mountains, or they can bounce back from each other. (S 13 & 14)
Transform: When plates rub against each other they alternate between being locked in place
and moving in sudden violent jumps, earthquakes. (S 15 & 16)
As pressure builds between them there is a point at which rocks break allowing the plates to
move, relieving the pressure in the form of vibrations that spread outward from the center of
the motion. (S 17)
Fault – Break in the crust along which movement takes place
Focus – Point at which the motion of the plates occurs along the fault.
Epicenter – point on the surface directly above the focus. The epicenter is the place where the
earthquake is first noticed and strongest
The vibrations sent out by an earthquake are called Seismic waves.
Rocks and Minerals:
(ppt: Rocks Cycle)
Minerals- naturally occurring, inorganic solids with a definite chemical composition and a
crystalline shape
Minerals are formed by:
Cooling magma/lava
Evaporation of salt water
Around 2,500 minerals exist of which 100 are common. 20 are referred to as “Rock Forming”
since they make up the majority of the rocks on Earth.
Rocks- A hard substance made up of one or more mineral or mineral-like substances
Rock Types: (based on formation)
Three types:
1) Igneous rocks - Rock made from the cooling of molten materials
2) Sedimentary rocks - Rock made by compacting and cementing of sediments (Lithification)
3) Metamorphic rocks - Rock changed by heat, pressure or chemical reactions into a new type
of rock
Rock Cycle: - Process by which rocks change between the three types of rocks.
At any point in the rock cycle there are three possible processes that can take place:
1)
Rocks can undergo weathering, erosion and deposition to produce sediments that will
become cemented together to form sedimentary rocks.
Weathering - The breakdown of materials on the Earth's surface.
Erosion: - The process by which weathered materials are moved away from their
present locations.
Deposition: - The process by which sediments is laid down in a new location.
2) Rocks can melt to form new magma which will eventually cool to form igneous rock.
3) Metamorphism - Heat, pressure and/or chemical changes can cause rocks to change
producing metamorphic rock.
Go over sequence
(Slides 1 – 11)
Handout: Blank Rock Cycle to be filled in by groups.
Filled in Rock Cycle
(Slide 12)