Presentation is loading. Please wait.

Presentation is loading. Please wait.

Anne M. Hofmeister and Robert E. Criss An Alternative view of Earth’s Beginnings.

Similar presentations


Presentation on theme: "Anne M. Hofmeister and Robert E. Criss An Alternative view of Earth’s Beginnings."— Presentation transcript:

1 Anne M. Hofmeister and Robert E. Criss An Alternative view of Earth’s Beginnings

2 Anne M. Hofmeister and Robert E. Criss Geophysics Heat transfer Geochemistry Meteorite chemical composition Isotopic data Thermodynamics Astronomy Orbits, mass, spin of planets and stars sources: Hofmeister and Criss 2012 Planetary and Space Science 62, p Gondwana Research 24, p. 490– Journal of Earth Science, in press. An Alternative view of Earth’s Beginnings

3 Earth’s current state stems from conditions of formation and differentiation which we infer from conservation laws and physical evidence ~Upright spin Coplanar,~circular orbits From NASA and /

4 R.E. = ½I  2 Current solar system energies depend strongly on self-gravitational potential

5 Initial spin energies: M50: Irwin J. et al. (2009) MNRAS, 392, M35: Meibom S., Mathieu R. D., Stassun K. G. (2009) ApJ, 695,

6 Initial spin energies : r orbit M central r cloud M

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 Wrong about star light Cp is negative Data and thermodynamics show that gravitational contraction cannot cause heat production Kelvin assumed U g = positive = total energy The heating idea predates nuclear reactions or fast-spinning stars If U g = total positive E Influx of heat (light) can cool the nebula below 0 K

9 Total E = P.E. + K.E. = F(V,T) Wrong about star light Cp is negative Data and thermodynamics show that gravitational contraction cannot cause heat production Kelvin assumed U g = positive = total energy The heating idea predates nuclear reactions or fast-spinning stars If U g = total positive E Influx of heat (light) can cool the nebula below 0 K -  U g   R.E.

10 Forming layers wherein radioactive isotopes rise upwards greatly cooled the Earth A globe with homogeneously distributed radioactive elements would be astronomically hot

11  U gE = -  R.E. + S Ef  T E + T Ei  S E The signs of the terms show that T E rises insignificantly Core formation ordered the Earth, promoted cooling, and possibly created differential rotation If frictional heating occurs: ½ the heat goes up and ½ goes down layer

12 Reactions amongst phases are expected at high T: Fe 0 + CO  FeC + FeO FeO + MgSiO 3 (enstatite)  (Mg,Fe)SiO 4 (olivine) FeO+5Mg 2 SiO 4 (forsterite)  5(Mg 0.9 Fe 0.1 ) 2 SiO 4 +MgO Core formation is one example of the general process of global density stratification via magmatism and outgassing in the hot early Earth: Due to gravitational acceleration increasing upwards, sorting among mantle minerals occurred Ices (CO, CO 2, H 2 O) Silicates (enstatite) Oxides (CAI’s) Metal (Fe)  depth g hot particles U, Th melts, gases

13 Earth’s gross composition can be inferred from its radioactive emissions and meteorite data Silicates Chondrites CAIs Calcium Aluminum Inclusions Oxygen isotopes of meteorites require two reservoirs

14 Meteorite reservoirs have similar mass proportions as zones in the present Earth Refractories ~3.8 g/cm 3 Lower Mantle 30% by mass O, Ca, Al, Mg, Si C Some Fe, Ti Metals ~7 g/cm 3 Silicates <3 g/cm 3 Crust + Upper mantle + Transition zone 17% by mass O, Mg, Si, Fe Some Ca, Na, Al, K Includes lithophiles such as U and Th, which originated in the refractory reservoir but were carried upwards early on by magmas. Core 50% by mass Fe,Ni,C,S,N

15 Gravitational contraction produces spin; whereas accretionary and core heating are inconsequential Earth dissipates its radioactive heat by magmatism (outgassing important early on) conduction convection (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 Summary


Download ppt "Anne M. Hofmeister and Robert E. Criss An Alternative view of Earth’s Beginnings."

Similar presentations


Ads by Google