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Inside the Earth. Composition (What is the earth made of?). depths. Each depth is discussed again later. The Core. Made mostly of iron 1/3 of the earth ’ s mass Very hot Made of two parts…(next slides). The Inner Core.
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depths • Each depth is discussed again later.
The Core • Made mostly of iron • 1/3 of the earth’s mass • Very hot • Made of two parts…(next slides)
The Inner Core • Begins 4000 miles (5200km) beneath the crust and is 800 miles (1,200 km) thick. 6,400 km at the middle. • 5000C – similar to sun’s surface • 45,000,000 PSI pressure (3,000,000 times air pressure at sea level) is so great that metals are not able to move about as a liquid. • Solid, crystalizing. Mainly Fe (Iron) and Ni alloy. S, O, C, Si likely.
The Outer Core • Goes from 2,900km – 5200km deep (2300 km thick) • Liquid iron and nickel alloy because even though temperature is lower than core, pressure is lower as well. • 4400-6100C • Eddy (counter-clockwise?) currents due to heat from inner core are thought to generate the earth’s magnetic fields. The magnetic field reaches from inner core all the way to where the solar wind affects the
Confusion? • The inner core is solid and hotter. Under more pressure. • The outer core is liquid and cooler. Under less pressure. • The inner core transfers heat to the outer core. • The inner core was much warmer a long time ago. So warm in fact, that it was actually probably liquid as well. • As the inner and outer cores cool, the outer core “freezes” onto the inner core causing it to grow larger by about 1mm a year. This growth is thought to affect the magnet field in the outer core. (See article: What drives earth’s magnetic field).
Magnetic Field How? • Read article “What drives Earth’s Magnetic Field.”
Magnetic Field Help • The magnetic field creates a protective bubble around the earth, deflecting the solar winds. Without this protection, the atmosphere could have been blown away, as predicted on Mars. No atmosphere, no life.
Bow Shock • Bow shock is a boundary between two atmospheric forces. • Stars: boundary between stellar wind and interstellar medium • Magnetic planets: boundary between magnetopause (magnetic field boundary) and solar wind.
Aurora Borealis • Auroras are caused by high energy particles from the solar wind that are trapped in the Earth's magnetic field. As these particles spiral back and forth along the magnetic field lines, they come down into the atmosphere near the north and south magnetic poles where the magnetic field lines disappear into the body of the Earth.
Aurora Borealis • The delicate colors are caused by energetic electrons colliding with oxygen and nitrogen molecules in the atmosphere. This excites the molecules, and when they decay from the excited states they emit the light that we see in the aurora.
The Mantle • 500 – 900C • Middle layer • Upper is solid – part of the lithosphere and tectonic plates • Lower is weak flow (“plastic” named by a solid’s ailty to flow being called plasticity) – top part is asthenosphere and where we see magma • Very thick layer composed of ferro-magnesium silicate • 2/3 earth’s mass • Large convection cells in lower mantle circulate heat and may drive plate tectonics. (heated material becomes less dense and rises, then cools, becomes more dense and sinks).
Tectonic Plates • Earth’s crust is broken into about 19 pieces • These plates move on top of the asthenosphere
Mantle Exposed • In some places in the crust (often in oceanic crust), the crust is non-existent and the mantle is exposed. • Midway between Cape Verde Islands and the Caribbean Sea is one such place.
The Crust • Outer layer, as thin as apple peel. Makes up 1% of the earth. • Composed mostly of alumino-silicates (insoluble metal salt with silicon and quartz– especially in the crust) Si, Al, Ca, Na, K • 70% water, 30% land • Temperature ranges from air temp to 870C deeper down. (Bread bakes at 175C and rocks melt at 870C). • Earthquakes and volcanoes erupt here • 2 types of crust • Oceanic (very dense, made of basalt) 5-10 km thick • Continental (less dense, made of granite) 35-70 km thick
Lithosphere and Asthenosphere • Lithosphere is the crust and solid portion of the upper mantle. Divided into tectonic plates. “Floats” on asthenosphere. 80 km thick. • Asthenosphere is much weaker than the lithosphere. 100-500 km below crust. Upper part of lower mantle. • The rest of the mantle is sometimes referred to as the mesosphere. (Not to be confused with the atmospheric mesosphere. The Asthenosphere
How do they know that? • 1936 - seismologist Inge Lehmann detected earthquake-generated seismic waves reflected from the inner core boundary to determine the existence of a solid core. The boundary between the inner core and outer core is referred to as Bullen discontinuity or sometimes Lehmann discontinuity. • It was believe the core was iron in 1940 and rigidity confirmed in 1971. • The outer core was believed to be liquid due to its inability to transmit elastic shear waves; only compressional waves are observed to pass through it Elastic shear waves should pass through the inner core but it is difficult to track them as they need to go through the outer core first and cannot.
