Presentation on theme: "Anne M. Hofmeister and Robert E. Criss"— Presentation transcript:
1 Anne M. Hofmeister and Robert E. Criss An Alternative view of Earth’s BeginningsAnne M. Hofmeister and Robert E. Criss
2 An Alternative view of Earth’s Beginnings Anne M. Hofmeister and Robert E. CrissGeophysicsHeat transferGeochemistryMeteorite chemical compositionIsotopic dataThermodynamicsAstronomyOrbits, mass, spin of planets and starssources: Hofmeister and Criss 2012 Planetary and Space Science 62, p2013 Gondwana Research 24, p. 490–500.2015 Journal of Earth Science, in press.
3 Coplanar,~circular orbits Earth’s current state stems from conditions of formation and differentiation which we infer from conservation laws and physical evidence~Upright spinCoplanar,~circular orbitsFrom NASA and/
4 Current solar system energies depend strongly on self-gravitational potential R.E. = ½Iw2
5 Initial spin energies: M35: Meibom S., Mathieu R. D., Stassun K. G. (2009) ApJ, 695,M50: Irwin J. et al. (2009) MNRAS, 392,
7 Orbital energies of planets provide evidence of conservation of mechanical energy and conservation of orbital angular momentum during 3-d collapse.Details in Planetary and Space Science (2012)
8 Data and thermodynamics show that gravitational contraction cannot cause heat production The heating idea predates nuclear reactions or fast-spinning starsKelvin assumed Ug = positive = total energyWrong aboutstar lightIf Ug = total positive ECp is negativeInflux of heat (light) can cool the nebula below 0 K
9 Data and thermodynamics show that gravitational contraction cannot cause heat production The heating idea predates nuclear reactions or fast-spinning starsKelvin assumed Ug = positive = total energyWrong aboutstar lightIf Ug = total positive ECp is negativeInflux of heat (light) can cool the nebula below 0 K-DUg DR.E.Total E = P.E. + K.E. = F(V,T)
10 A globe with homogeneously distributed radioactive elements would be astronomically hot Forming layers wherein radioactive isotopes rise upwards greatly cooled the Earth
11 Core formation ordered the Earth, promoted cooling, and possibly created differential rotation If frictional heating occurs:½ the heat goes up and ½ goes downlayerDUgE = -DR.E. + SEfDTE + TEiDSEThe signs of the terms show that TE rises insignificantly
12 Core formation is one example of the general process of global density stratification via magmatism and outgassing in the hot early Earth:Ices (CO, CO2, H2O)Silicates (enstatite)Oxides (CAI’s)Metal (Fe)ghot particlesU, Thmelts, gasesrdepthDue to gravitational acceleration increasing upwards, sorting among mantle minerals occurredReactions amongst phases are expected at high T:Fe0 + CO FeC + FeOFeO + MgSiO3 (enstatite) (Mg,Fe)SiO4 (olivine)FeO+5Mg2SiO4(forsterite)5(Mg0.9Fe0.1)2SiO4+MgO
13 Earth’s gross composition can be inferred from its radioactive emissions and meteorite data SilicatesChondritesOxygen isotopes of meteorites require two reservoirsCAIsCalcium Aluminum Inclusions
14 Crust + Upper mantle + Transition zone Meteorite reservoirs have similar mass proportions as zones in the present EarthCrust + Upper mantle + Transition zone17% by massO, Mg, Si, FeSome Ca, Na, Al, KIncludes lithophiles such as U and Th, which originated in the refractory reservoir but were carried upwards early on by magmas.Silicates<3 g/cm3Refractories~3.8 g/cm3Metals~7 g/cm3Lower Mantle30% by massO, Ca, Al, Mg, SiCSome Fe, TiCore50% by massFe,Ni,C,S,N
15 SummaryGravitational contraction produces spin; whereas accretionary and core heating are inconsequentialEarth dissipates its radioactive heat bymagmatism (outgassing important early on)conductionconvection (upper mantle only and slow)The chemically distinct lower mantle, for which we have no samples, is derived from the refractory CAI reservoir, but is now nearly devoid of heat-producing elements
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