Inside the EarthInside the Earth

Composition (What is the earth Composition (What is the earth made of?)made of?)

depthsdepths

• Each depth is Each depth is discussed again later. discussed again later.

The CoreThe Core

• Made mostly of ironMade mostly of iron

• 1/3 of the earth1/3 of the earth’’s s massmass

• Very hotVery hot

• Made of two parts…Made of two parts…(next slides)(next slides)

The Inner CoreThe Inner Core

• Begins 4000 miles Begins 4000 miles (5200km) beneath the (5200km) beneath the crust and is 800 miles crust and is 800 miles (1,200 km) thick. 6,400 km (1,200 km) thick. 6,400 km at the middle.at the middle.

• 5000C – similar to sun’s 5000C – similar to sun’s surfacesurface

• 45,000,000 PSI pressure 45,000,000 PSI pressure (3,000,000 times air (3,000,000 times air pressure at sea level) is so pressure at sea level) is so great that metals are not great that metals are not able to move about as a able to move about as a liquid.liquid.

• Solid, crystalizing. Mainly Solid, crystalizing. Mainly Fe (Iron) and Ni alloy. S, O, Fe (Iron) and Ni alloy. S, O, C, Si likely.C, Si likely.

The Outer CoreThe Outer Core

• Goes from 2,900km – 5200km Goes from 2,900km – 5200km deep (2300 km thick) deep (2300 km thick)

• Liquid iron and nickel alloy Liquid iron and nickel alloy because even though because even though temperature is lower than temperature is lower than core, pressure is lower as well.core, pressure is lower as well.

• 4400-6100C4400-6100C

• Eddy (counter-clockwise?) Eddy (counter-clockwise?) currents due to heat from inner currents due to heat from inner core are thought to generate core are thought to generate the earth’s magnetic fields. the earth’s magnetic fields. The magnetic field reaches The magnetic field reaches from inner core all the way to from inner core all the way to where the solar wind affects where the solar wind affects the the

Confusion?Confusion?

• The inner core is solid and hotter. Under more pressure.The inner core is solid and hotter. Under more pressure.

• The outer core is liquid and cooler. Under less pressure. The outer core is liquid and cooler. Under less pressure.

• The inner core transfers heat to the outer core. The inner core transfers heat to the outer core.

• The inner core was much warmer a long time ago. So The inner core was much warmer a long time ago. So warm in fact, that it was actually probably liquid as warm in fact, that it was actually probably liquid as well. well.

• As the inner and outer cores cool, the outer core As the inner and outer cores cool, the outer core “freezes” onto the inner core causing it to grow larger “freezes” onto the inner core causing it to grow larger by about 1mm a year. This growth is thought to affect by about 1mm a year. This growth is thought to affect the magnet field in the outer core. (See article: What the magnet field in the outer core. (See article: What drives earth’s magnetic field). drives earth’s magnetic field).

Magnetic Field How?Magnetic Field How?

• Read article “What drives Earth’s Magnetic Field.”Read article “What drives Earth’s Magnetic Field.”

Magnetic Field HelpMagnetic Field Help

• The magnetic The magnetic field creates a field creates a protective protective bubble around bubble around the earth, the earth, deflecting the deflecting the solar winds. solar winds. Without this Without this protection, the protection, the atmosphere atmosphere could have could have been blown been blown away, as away, as predicted on predicted on Mars. No Mars. No atmosphere, no atmosphere, no life. life.

Bow ShockBow Shock

• Bow shock is a boundary Bow shock is a boundary between two atmospheric between two atmospheric forces. forces.

• Stars: boundary between Stars: boundary between stellar wind and stellar wind and interstellar mediuminterstellar medium

• Magnetic planets: Magnetic planets: boundary between boundary between magnetopause (magnetic magnetopause (magnetic field boundary) and solar field boundary) and solar wind. wind.

Aurora BorealisAurora Borealis

• Auroras are caused by Auroras are caused by high energy particles high energy particles from the solar wind from the solar wind that are trapped in the that are trapped in the Earth's magnetic field. Earth's magnetic field. As these particles As these particles spiral back and forth spiral back and forth along the magnetic along the magnetic field lines, they come field lines, they come down into the down into the atmosphere near the atmosphere near the north and south north and south magnetic poles where magnetic poles where the magnetic field the magnetic field lines disappear into lines disappear into the body of the Earth.the body of the Earth.

Aurora BorealisAurora Borealis

• The delicate The delicate colors are caused colors are caused by energetic by energetic electrons electrons colliding with colliding with oxygen and oxygen and nitrogen nitrogen molecules in the molecules in the atmosphere. This atmosphere. This excites the excites the molecules, and molecules, and when they decay when they decay from the excited from the excited states they emit states they emit the light that we the light that we see in the aurora.see in the aurora.

The MantleThe Mantle• 500 – 900C500 – 900C

• Middle layerMiddle layer• Upper is solid – part of the Upper is solid – part of the

lithosphere and tectonic plateslithosphere and tectonic plates• Lower is weak flow (“plastic” Lower is weak flow (“plastic”

named by a solid’s ailty to flow named by a solid’s ailty to flow being called plasticity) – top part being called plasticity) – top part is asthenosphere and where we is asthenosphere and where we see magmasee magma

• Very thick layer composed of Very thick layer composed of ferro-magnesium silicateferro-magnesium silicate

• 2/3 earth’s mass2/3 earth’s mass

• Large convection cells in lower Large convection cells in lower mantle circulate heat and may mantle circulate heat and may drive plate tectonics. (heated drive plate tectonics. (heated material becomes less dense and material becomes less dense and rises, then cools, becomes more rises, then cools, becomes more dense and sinks). dense and sinks).

Tectonic PlatesTectonic Plates

• EarthEarth’’s crust is broken into about 19 piecess crust is broken into about 19 pieces

• These plates move on top of the asthenosphereThese plates move on top of the asthenosphere

Mantle ExposedMantle Exposed• In some places in the crust (often in oceanic In some places in the crust (often in oceanic

crust), the crust is non-existent and the mantle crust), the crust is non-existent and the mantle is exposed. is exposed.

• Midway between Cape Verde Islands and the Midway between Cape Verde Islands and the Caribbean Sea is one such place. Caribbean Sea is one such place.

Composition of Mantle Composition of Mantle in Wieght %in Wieght %

Element Amount Compound Amount

O 44.8

Si 21.5 SiO2 46

Mg 22.8 MgO 37.8

Fe 5.8 FeO 7.5

Al 2.2 Al2O3 4.2

Ca 2.3 CaO 3.2

Na 0.3 Na2O 0.4

K 0.03 K2O 0.04

Sum 99.7 Sum 99.1

The CrustThe Crust

• Outer layer, as thin as apple peel. Outer layer, as thin as apple peel. Makes up 1% of the earth. Makes up 1% of the earth.

• Composed mostly of alumino-Composed mostly of alumino-silicates (insoluble metal salt with silicates (insoluble metal salt with silicon and quartz– especially in the silicon and quartz– especially in the crust) Si, Al, Ca, Na, Kcrust) Si, Al, Ca, Na, K

• 70% water, 30% land70% water, 30% land

• Temperature ranges from air temp Temperature ranges from air temp to 870C deeper down. (Bread to 870C deeper down. (Bread bakes at 175C and rocks melt at bakes at 175C and rocks melt at 870C).870C).

• Earthquakes and volcanoes erupt Earthquakes and volcanoes erupt herehere

• 2 types of crust2 types of crust• Oceanic (very dense, made of Oceanic (very dense, made of

basalt) 5-10 km thickbasalt) 5-10 km thick• Continental (less dense, made of Continental (less dense, made of

granite) 35-70 km thick granite) 35-70 km thick

Oceanic and Oceanic and Continental CrustContinental Crust

Lithosphere and Lithosphere and AsthenosphereAsthenosphere

• Lithosphere is the crust and solid portion of the upper Lithosphere is the crust and solid portion of the upper mantle. Divided into tectonic plates. “Floats” on mantle. Divided into tectonic plates. “Floats” on asthenosphere. 80 km thick.asthenosphere. 80 km thick.

• Asthenosphere is much weaker than the lithosphere. 100-Asthenosphere is much weaker than the lithosphere. 100-500 km below crust. Upper part of lower mantle. 500 km below crust. Upper part of lower mantle.

• The rest of the mantle is sometimes referred to as the The rest of the mantle is sometimes referred to as the mesosphere. (Not to be confused with the atmospheric mesosphere. (Not to be confused with the atmospheric mesosphere. mesosphere.

The Asthenosphere

Crusty Action 1Crusty Action 1

Crusty Action 2Crusty Action 2

Layers ReviewLayers Review

Layers ReviewLayers Review

Food for ThoughtFood for Thought

How do they know How do they know that?that?

• 1936 - seismologist Inge Lehmann 1936 - seismologist Inge Lehmann detected earthquake-generated detected earthquake-generated seismic waves reflected from the inner seismic waves reflected from the inner core boundary to determine the core boundary to determine the existence of a solid core. The existence of a solid core. The boundary between the inner core and boundary between the inner core and outer core is referred to as Bullen outer core is referred to as Bullen discontinuity or sometimes Lehmann discontinuity or sometimes Lehmann discontinuity.discontinuity.

• It was believe the core was iron in It was believe the core was iron in 1940 and rigidity confirmed in 1971. 1940 and rigidity confirmed in 1971.

• The outer core was believed to be The outer core was believed to be liquid due to its inability to transmit liquid due to its inability to transmit elastic shear waves; only elastic shear waves; only compressional waves are observed to compressional waves are observed to pass through it Elastic shear waves pass through it Elastic shear waves should pass through the inner core but should pass through the inner core but it is difficult to track them as they it is difficult to track them as they need to go through the outer core first need to go through the outer core first and cannot. and cannot.

Making WavesMaking Waves

The EndThe End