Chemical Layers
Crust, mantle, and core
Crust
- outermost layer of the Earth.
-5-100 km thick.
-earth's thinnest layer.
-scentists know more about the crust than the mantle and/or core.
2 Types of Crust
Continental crust and Oceanic crust
Continental Crust
-has a composition simiar to granite.
-has an average thickness of 30 km.
Oceanic Crust
-has a composition simiar to basalt.
-generally between 5 and 8 km thick.
Oceanic Crust is denser than Continental Crust
basalt is denser than granite.
Mantle
-lies between the Crust and the Core.
-2,900 km thick.
-contains 67% of the earth's mass.
-most observations of the mantle are made from the earth's surface.
-in some places, tectonic activity has pushed rock from the mantle to the earth's surface allowin
Core
-extends from the bottom of the mantle to center of the earth.
-Composed mainly of Fe with smaller amounts of Ni, and possible S and O.
-33% of the earth's mass.
-6.856 km in diameter
-The earth's core is slightly larger than Mars.
Earth's structure - physical layers
Lithosphere, asthenosphere, mesosphere, outer core and inner core.
Lithosphere
outermost, rigid layer "rock spheres". 15-300 km thick. Made of the crust and the rigid uppermost part of the mantle. Divided into pieces called tectonic plates.
Asthenosphere
Weak sphere. 250 km thick. Sfot layer of the mantle on which pieces of the lithosphere move. Made of solid rock (similar to putty) that flows very slowly.
Mesosphere
Middle sphere. 2,550 km thick. Strong, lower part of the mantle. Extends from the bottom of the asthenosphere to the earth's core.
Outer core
2,200 km thick. Liquid layer of the earth's core. Lies beneath the mantle and surrounds the inner core.
Inner core
1,228 km thick. Solid and dense. Extends from the bottom of the outer core and extends to the earth's center.
Tectonic plates
Pieces of the lithosphere that move on top of the asthenosphere. 10 major plates. Some have continental and oceanic crust, others have just oceanic crust. Fit together like pieces of a jigsaw puzzle. Plates vary in thickness and what we see is only a part
Mapping the Earth's interior
Earthquakes provide us with information about the earth's interior. Seismic waves (vibrations caused by earthquakes) travel through the earth. Travel at different speeds depending on the materials through which they pass. Seismic waves travel faster throu
Continental Drift
Devised by Alfred Wegener in the early 1900s. Theory stating that continents can drift from one another and have done so in the past. Explain why continents "fit" together. Explains why fossils of the same plant and animals species are found on different
Panagaea
Large, single super continent that existed on the earth 245 million years ago. Some of the earliest dinosaurs lived here. Panthalassa is the large ocean that surrounded it.
180 million years ago
Panagea broke into Northern continent Laurasia and Southern continent, Gondwana.
65 million years ago
Laurasia split into North America, Europe, and most of Asia. Gondwana split into South America, Africa, Australia, Antarctica and India.
Sea-Floor Spreading
The process by which new oceanic lithosphere is created as older materials are pulled away. As tectonic plates move away from each other, the sea floor spreads apart and new magma fills in the gap. The closer to the ridge, the new the crust. The oldest cr
Magnetic Reversals
Occurs when the earth's magnetic north and south poles change place. Occured many times in the earth's history. The molten rock along mid-ocean ridges contain grains of magnetic minerals. As the rock cools, the minerals align according to the orientation
Plate tectonics
Theory states that the earth's lithosphere is divided into tectonic plates that move above the asthenosphere.
Possible reasons for tectonic plate movements
Ridge push. Convection. Slab pull.
Ridge push
The process by which an oceanic plate slides down the lithosphere-asthenosphere boundary. At mid-ocean ridges, the oceanic lithosphere is higher than it is where it sinks beneath continental lithosphere.
Convection
Hot material from deep within the earth rises (become less dense) while cooler material near the surface sinks (increases in density). The motion of convection currents drags tectonic plates sideways.
Slab pull
The denser oceanic lithosphere sinks into the asthenosphere when it collides with continental lithosphere. As the oceanic plate sinks, it pulls the rest of the plate with it.
Tectonic plate boundaries
Convergent. Divergent. Transform.
Convergent boundaries
Boundary where two tectonic plates collide. 3 types of convergent boundaries.
Continental/Continental collisions
When two tectonic plates with continental crust collide, the buckle and thicken. Mountains are formed.
Continental/Oceanic collisions
Oceanic plate slides under the continental plate. Subduction zone - the area there the oceanic plate sinks into the asthenosphere.
Oceanic/Oceanic collisions
Subduction occurs similar to continental/oceanic collisions.
Divergent boundaries
When two tectonic plates move away from each other. Found at mid-ocean ridges (sea-floor spreading). Magma rises to fill the gap. Can also be found on continents.
Transform boundaries
When plates slide past each other horizontally. Plates are not smooth and grind and jerk as they slide. Earthquakes are produced. San Andreas fault is a good example. Tectonic plate movements are measured with a global positioning system (GPS).
Stress
The amount of force unit area that is put on a given material. Causes deformation. Compression and tension are 2 types of stress.
Compression
Occurs when an object is squeezed. Occurs when an object is squeezed. Occurs at convergent boundaries. Formed the Rocky Mountains and the Cascade Range.
Tension
Occurs when forces act to stretch an object. Occurs at divergent boundaries.
Folding
Occurs due to compression. Syncline,anticline,monocline. Small folds can be measured in cm and large folds can be measured in km.
Fault
The surface along which rocks break and slide past each other.
Fault block
Blocks of crust on each side of the fault.
Faults that are not vertical have a hanging wall and a footwall.
The type of fault may be determined by looking at the sequence of the rock layers.
Hanging wall
Block of crust above the fault.
Footwall
Block of crust below the fault.
Normal fault
The hanging wall moves down in relation to the footwall. Usually result from the tensional stress.
Reverse fault
The hanging wall moves up in relation to the footwall. Usually result from the compressional stress.
Strike-slip faults
Occur at transform boundaries. Plate tectonics and mountain building. Mountains ranges form because of the continuous movements of tectonic plates. Compression and tension can form different types of mountains.
Folded mountains
Formed by compression (convergent boundaries). Appalachians, Rockies, Himalayas. Appalachians formed ~ 390 million years ago when North America and African plates collided. The plates drifted apart ~208 million years ago and mid-ocean ridge formed in the
Fault-block mountains
Form due to tension. Form when normal faults cause large blocks of the earth's crust to drop down relative to the other blocks. Grand Tetons.
Volcanic mountains
Form when molten rock erupts onto the earth's surface. Occurs at convergent boundaries that include subduction zones,. Form from a new material being added to the earth's surface (differs from folded and fault-block mountains). Predominant mountains in th