Plate Tectonics Earth’s InteriorLayers of the Earth Drifting ContinentsPlate Boundaries
1. Earth’s Interior • We know about the earth’s interior from indirect evidence • Example of indirect evidence: Finding where to hang a picture so that it stays hung solidly • Temperature and pressure change • Temperature increases towards the center of the earth • Pressure also increases towards the center
Cross-section of earth’s interior showing crust, mantle and the two parts of the core
Four Main Layers of the Earth’s Interior • The crust – the layer of rock that forms the earth’s outer skin, includes rocks, mountains, soil and water • The mantle – 5-40 km down. Rock is of hotter temperatures. About 3,000 km thick • The core – two parts: outer core which is molten meltal and inner core which is solid metal
Earth’s Magnetic Field Currents in the liquid outer core force the solid inner core to spin at a slightly faster rate than the rest of the planet. These currents in the outer core create the magnetic field causing the earth to act like a giant bar magnet.
2. Convection Currents and the Mantle • In the upper most part of the Mantle is a rigid layer called the lithosphere. Litho means rocky or stone. • Below the lithosphere is the asthenosphere, which means weak, but it is actually semi-molten and the semi-melted rock is moving in slow currents!
Convection Convection is heat transfer by movement of heated fluid (gas or liquid). Heat transfer by convection is caused by differences of temperature and density within that fluid The heating and cooling of the fluid, changes in the fluid’s density, and the force of gravity all combine to set convection going in the earth’s mantle.
These convection cells move sections of the crust. Hot, less dense molten lava rises to the surface creating new crustal sections. Old crust is “subducted” down in the earth, melting and recycling!
3. Drifting Continents • 1910 Alfred Wegener hypothesized that all the continents had once been joined together in a single landmass and have since drifted apart. • Evidence includes mountain ranges that line up, fossils that were similar, mineral deposits that also lined up, and climate evidence and traces • Most scientists at the time did not believe in this theory of drifting continents, as Wegener could not explain what force was actually moving the continents.
4. Sea-Floor Spreading • Mapping the Mid-Ocean Ridge – the longest chain of mountains in the world! • Sonar mapping(begun in 1959) revealed the location of these Mountains
Evidence of Sea-Floor Spreading • Ocean floors move like conveyor belt, carrying the continents along with them. • At the mid-ocean ridge, molten material rises from the mantle and erupts. The molten material then spreads out, pushing older rock to both sides of the ridge.
Evidence of Sea-Floor Spreading • Molten material found erupting along mid-ocean ridge • Iron within basaltic crust was magnetized. Strips on either side of the mid-ocean ridge matched up
Subduction at Deep-Ocean Trenches Trenches – forms where the oceanic crust is thrust back down into the mantle and begins cracking and melting
How islands are formed: Hot spots in the crust allow melted magma to form little cones on the ocean floor that build higher and higher to form islands.