The Earth; A Dynamic Planet
Lesson 1 "The Earth's Layers"
- Crust -The outer layer of the Earth. The crust consists of ocean plates and continental plates. The crust is composed of light material called rock. The crust and the outer layer of the mantle together are called the lithosphere. The lithosphere is very brittle and light and moves because of convection currents in the lower layer of the mantle called the asthenosphere.
- Oceanic Crust -Made of dense basaltic rock. Oceanic plates carry the continental plates across the surface of the Earth.
- Continental Crust -Made of light granitic rock. Continental crust rides on the oceanic crust.
- Lithosphere - The crust and the upper rigid layer of the mantle seem to move together and form the plates of the Earth.
- Mantle -Largest layer of the Earth located directly under the crust. The mantle is composed of very hot, dense, flowing rock. The material in the mantle flows because of convection currents.
- Asthenosphere - Lower layer of the mantle. This is the layer that flows and moves the plates of the Earth. Flows very slowly with the consistency of hot asphalt under pressure.
- Convection Currents - are a circular current caused by the difference in temperatures from the bottom to the top of the mantle. It is because of these currents that the plates of the Earth have moved in the past and are moving today. These plate movements cause earthquakes, mountain building, and volcanism.
- Outer Core -The layer located directly under the mantle. The outer core is composed of liquid nickel and iron. Scientists believe that the outer core is liquid because S waves from an earthquake bounce of the layer instead of passing through it.
- Inner Core -The inner core is composed of nickel and iron under such great temperatures and pressures that the metals are in a solid state of motion.
Lesson Two- "Pangaea to the present"
- Dynamic Planet -The Earth's surface is very slowly but constantly changing. The plates are moving causing earthquakes that reshape the land, mountain building, and volcanism that also dramatically reshapes the surface.
- Plates -The thin, fragile, and rigid lithosphere is broken up into 12 main plates. These plates move very slowly at about 1 inch to 4 inches per year.
- Plate Tectonics/Continental Drift Theory -Alfred Wegener, a German scientist proposed this theory that states that the Earth's surface is broken into pieces that move and have moved for millions of years. Wegener did not know the mechanism that moved the plates, and his theory was rejected until the 1960's when scientists studied the ocean floor and found the mid-ocean ridges (sea floor spreading zones).
- Pangaea -Super continent 250 million years ago. The seven continents were all connected together into one huge land mass.
- Panthalassa -The gigantic ocean 250 million years ago. It was the predecessor to the Pacific Ocean.
- Laurasia -About 200 million years ago Pangaea began to break up. The northern part which consisted of North America, Asia, and Europe was then called Laurasia.
- Gondwanaland -The southern part after the split up of Pangaea was called Gondwanaland. Gondwanaland consisted of South America, Africa, Antarctica, Australia and the subcontinent of India.
- Plate Boundaries
- Convergent -A boundary in which two plates collide causing
1) immense mountain building (Ex: Indian plate and the Eurasian plate forming the Himalayan Mountains) and
2) one plate riding above the other driving the thinner denser plate down into the mantle creating a subduction zone.
- Divergent -A boundary in which two plates are separating. The two plates are moving in opposite directions and as they spread apart magma fills the void causing the formation of new crust. Divergent boundaries cause the oceans to spread apart while convergent boundaries cause the oceans to shrink.
- Transform -A boundary in which two plates scrape and slide past each other. Transform boundaries are like tears in the Earth's crust. An example is the San Andreas Fault in California.
Lesson 3- How Plates Move
- Subduction Zone -Formed at a convergent plate boundary. One plate is lighter and thicker than the other causing the thinner denser plate to be driven down into the mantle. Subduction zones are areas of the world in which high amounts of earthquakes and volcanism is present. Subduction zones are ocean shrinking zones.
- Mid-ocean ridge -Formed at a divergent plate boundary. The worlds longest continuous mountain range over 40,000 miles long. Where the two plates separate lava fills the void causing new crust to be produced. Mid-ocean ridges are ocean spreading zones.
- Magma/Magma Chamber -Magma is molten rock under the Earth's surface. Magma is full of gas and under extreme pressures. Magma will collect in areas of weak rock far under the surface of the Earth in zones called magma chambers.
- Pyroclastic Rock -Pyroclastic is a Greek word that means "broken by fire". Pyroclasts are fragmented rock that is ejected from a volcano. Pyroclasts are classified by the size of the particle; ash is very small pieces of shattered rock. lapilli are pieces of shattered rock 1/10 of an inch to 2 inches in diameter. Blocks and bombs are larger pyroclasts ranging in size from 2 inches to several feet in diameter. Blocks are angular chunks of rock and bombs are rounded rock that takes its shape as it is hurled through the air.
- Trenches -Form at subduction zones. They are the deepest part of the oceans and the lowest points on the crust of the Earth.
- Formation of Mountains -
- Folded Mountains -Rollercoaster like formation. The plates of the Earth are pushed together and the impact forms the tallest mountains on Earth.
- Fault-block Mountains -The plates are pushed together and snap from the collision. These mountains have very rough linear peaks. Ex: The Grand Teton Mountains in Wyoming.
- Dome Mountains -These mountains form when plate collisions push an area of the crust up into a dome shape. The crust doesn't snap and break as in fault-block mountains. Ex: The Black Hills of South Dakota.