We have been talking about minerals primarily in the earth s crust What About the rest Mantle composition rheology dicontinuities Harzburgite 80 olv 20 OPX lithosphereLherzolite 60 olv 40 OPX grt MOHO asthenosphere Pyrolite lherzolite like Upper mantle Olivine spinel 410 Pyroxene spinel stishovite 660 Spinel Lower mantle perovskite periclase Upper Mantle Minerals Olivine 60 Pyroxene 30 Garnet 10 Rest is compositionally homogeneous discontinuities What s different Harzburgite 80 olv 20 OPX lithosphere Lherzolite 60 olv 40 OPX grt MOHO asthenosphere Pyrolite lherzolite like Upper mantle Olivine spinel 410 Pyroxene spinel stishovite Lower mantle Spinel perovskite periclase 660 Upper Mantle Olivine Olivine Thought to be about 10 12 Fe in upper mantle At pressures around the 410 km discontinuity Fo rich olivine transforms to a ccp structure called wadsleyite Iron rich olivines do not undergo this transformation At higher pressures both the Fa rich olivine and wadsleyite transform to a spinel structure Mg Fe 2SiO4 called ringwoodite This occurs when the pressure forces the structure to become as closest packed as it can get in order to become more dense it must transform to a new phase Garnet Pyroxene As pressure increases Pyroxene Garnet primarily pyrope Increases from 50 to 520 km Past 520 km Garnet Ca perovskite Past 720 km more Mg rich Garnets begin to form Mg perovskite Lower Mantle Minerals Perovskite Mg Fe SiO3 Magnesiow stite Mg Fe O and Stishovite SiO 2 80 Perovskite 20 Magnesiowustite minor stishovite which doesn t form if Mg or Fe are around At these high pressures all Si is 6coordinate SiO6 subunits Octahedral coordination Do we have any Lower Mantle Minerals NO How do we know they are there METEORITES P S waves tell us something about composition Nuclear chemistry also tells us something about composition EXPERIMENTS simulate P T see what you get Meteorite types Stony stony iron and iron Stony Chondritic or Achondritic Chondrules spherical bits of olive or pyroxene condensed from the hot soar nebula over 4 billion years ago Stony iron Composed of nickel iron metal and stony components mafic minerals Iron Nickel iron alloys Kamosite and Taenite Perovskite Mg Fe SiO3 As the major mineral in the lower mantle possibly the most abundant earth material Core Core Outer Core Liquid made of Iron Fe and Nickel Ni about 4 and some S Si and O enough to make the density less than Fe and Ni alone Movement of this liquid is responsible for earth s magnetic field Inner Core Solid Hexagonally closest packed Fe and Ni Earth Image taken by Voyager I in 1990 Photos taken 4 billion miles away from earth A mosaic image filtered and magnified We succeeded in taking that picture and if you look at it you see a dot That s here That s home That s us On it everyone you ever heard of every human being who ever lived lived out their lives The aggregate of all our joys and sufferings thousands of confident religions ideologies and economic doctrines every hunter and forager every hero and coward every creator and destroyer of civilizations every king and peasant every young couple in love every hopeful child every mother and father every inventor and explorer every teacher of morals every corrupt politician every superstar every supreme leader every saint and sinner in the history of our species lived there on a mote of dust suspended in a sunbeam The earth is a very small stage in a vast cosmic arena Think of the rivers of blood spilled by all those generals and emperors so that in glory and in triumph they could become the momentary masters of a fraction of a dot Think of the endless cruelties visited by the inhabitants of one corner of the dot on scarcely distinguishable inhabitants of some other corner of the dot How frequent their misunderstandings how eager they are to kill one another how fervent their hatreds Our posturings our imagined self importance the delusion that we have some privileged position in the universe are challenged by this point of pale light Our planet is a lonely speck in the great enveloping cosmic dark In our obscurity in all this vastness there is no hint that help will come from elsewhere to save us from ourselves It is up to us It s been said that astronomy is a humbling and I might add a character building experience To my mind there is perhaps no better demonstration of the folly of human conceits than this distant image of our tiny world To me it underscores our responsibility to deal more kindly and compassionately with one another and to preserve and cherish that pale blue dot the only home we ve ever known Formation of the Universe Courtesy JPL http cougar jpl nasa gov HR4796 anim html Formation of the Universe Courtesy JPL http cougar jpl nasa gov HR4796 anim html Planetary Geology How can we know anything about the geology of another planet Venus Clouds Magnetic field Geology Have we ever been there Data shows that most of the rocks are mafic basalts with seemingly little soil development make sense