Earth’s Layers

The Layers: Lower mantle Transition region

Layers of the Atmosphere The main layers are (beginning closest to the surface): 1.Troposphere (0-11 km above Earth’s surface) 2.Stratosphere (11-48 km above Earth’s surface) 3.Mesosphere (48-95 km above Earth’s surface) 4.Thermosphere (includes the ionosphere; km above Earth’s surface) 5.Exosphere (600 km above Earth’s surface to outer space)

Layers of the Atmosphere

Crust  On average 30 km thick  Oceanic: thinner…10km, mainly basalt (an igneous rock with small crystals)  Continental: thicker…75km, layering of igneous/sedimentary/metamorphic rocks, many rocks have larger crystals  12 moving plates constitute the Earth’s surface – the plates include oceanic and continental crust plus the upper mantle  Crust is constantly recycled – new crust is made at oceanic ridges when 2 plates are pulling apart and old crust plunges back into the Earth/melts when 2 plates collide

Moho Discontinuity The boundary between the crust and the mantle due to a change in rock mineral content (changes the density of the rocks). The change is gradual/not abrupt and is detected by the refraction of earthquake waves. What is refraction? Also, the boundary varies over time.

Mantle  Approximately from 30 km to 2900 km below the Earth’s surface.  The crust and upper mantle make up the rigid, brittle lithosphere (plates)  The lithosphere floats on top of the asthenosphere.  Temperature increases as you go deeper into the mantle – the lithosphere is solid but the asthenosphere is near its melting point. This allows the asthenosphere to flow in convection currents.  Do you remember how convection currents work? Explain!  Where does the heat come from that causes the asthenosphere to flow?  Is the asthenosphere a liquid or a solid?  The mesosphere is the name of the middle mantle. Sometimes its called the transition region. It contains Ca, Al, and garnet. These elements and minerals melt when hot to make basalt (hmm) and become buoyant.

Mantle (continued) Convection currents occur in the mantle and the atmosphere.

Mantle (continued) Convection currents allow a transfer of heat energy from one place to another.

Mantle (continued) Convection occurs only in fluids (liquids/gases), not in solids. Particles must be free to move about. When a fluid is heated, the molecules at the bottom move with bigger vibrations. They take up more space (volume) which means that the density goes down (decreases). The less dense fluid rises. Then it gives its energy to the fluid above and cools down. The molecules condense back together and take up less space which means that density goes back up (increases). The more dense fluid falls back to the bottom.

Other types of heat transfer Conduction: If you put a metal bar into a flame, it gets hot quickly. Soon you can't hold it. If you put a glass bar into a candle, it won't get too hot to hold. But if you touched the end that was in the flame, you would find that it was really hot! Heat passes through a solid substance to another solid substance while they are touching, always from hot molecules to cold molecules. Metals are good conductors of heat; non- metals/liquids/gases are generally bad conductors.

Heat is passed on as an electromagnetic wave (light wave) called infra-red radiation. All the heat from the Sun reaches us infra-red radiation. Our eyes cannot see infra-red, but a digital camera can. The hot plate appears much brighter than it actually is because of infra-red radiation. The hotter the object, the more radiation it emits. A heat sensitive camera shows the cat's nose is the hottest part. Other types of heat transfer Radiation:

Summary: 3 types of heat transfer Convection: movement of hot material moves heat energy (liquids and gases). Conduction: heat energy moves from the molecules of one solid to the molecules of another solid when they are touching. Radiation: heat energy travels as a wave, like a light wave.

Last Mantle Slide! Lower mantle: km, probably (Do you mean we don’t know for sure?) composed of Si, Mg, O, Fe, Ca and Al. (evidence from the cosmos) D Layer: 2,700-2,900 km, originally thought to be part of the lower mantle but may be too different and therefore a layer of its own. The difference may be that it has a different density ( ______ dense than the mantle and ______ dense than the outer core). (evidence from seismic waves)

Outer Core Liquid Fe and Ni (and possibly some S and O…again the cosmos thing). Convection currents occur here as well. The movement of the liquid outer core creates an electrical current that leads to Earth’s magnetic field.

Inner Core Solid Fe and Ni Hottest layer: °C Highest pressure: creates a solid rather than a liquid Highest density, most compact layer: g/cm 3 Inner and Outer core together make up 15% of Earth’s volume (Mantle=84%; Crust=1%): mass is packed into a tighter space therefore the density is higher

Quiz What creates all of these different layers? Density! Why are some of the layers solid and some of them liquid? Why are there differences in density? As pressure increases deeper in the Earth, mass gets compacted into a tighter space/smaller volume Temperature also increases as you go deeper inside the Earth. Although pressure causes substances to compact into a solid, high temperatures cause substances to melt into a liquid.