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

An Alternative view of Earth’s Beginnings 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. 111-131. 2013 Gondwana Research 24, p. 490–500. 2015 Journal of Earth Science, in press.

Coplanar,~circular orbits 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 http://test.glossopedia.org/solar-system /

Current solar system energies depend strongly on self-gravitational potential R.E. = ½Iw2

Initial spin energies: M35: Meibom S., Mathieu R. D., Stassun K. G. (2009) ApJ, 695, 679-694 M50: Irwin J. et al. (2009) MNRAS, 392, 1456-1466

Initial spin energies: rcloud M rorbit Mcentral

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)

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

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

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

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 DUgE = -DR.E. + SEfDTE + TEiDSE The signs of the terms show that TE rises insignificantly

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) g hot particles U, Th melts, gases r depth Due to gravitational acceleration increasing upwards, sorting among mantle minerals occurred Reactions amongst phases are expected at high T: Fe0 + CO  FeC + FeO FeO + MgSiO3 (enstatite)  (Mg,Fe)SiO4 (olivine) FeO+5Mg2SiO4(forsterite)5(Mg0.9Fe0.1)2SiO4+MgO

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

Crust + Upper mantle + Transition zone Meteorite reservoirs have similar mass proportions as zones in the present Earth 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. Silicates <3 g/cm3 Refractories ~3.8 g/cm3 Metals ~7 g/cm3 Lower Mantle 30% by mass O, Ca, Al, Mg, Si C Some Fe, Ti Core 50% by mass Fe,Ni,C,S,N

Summary 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