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

2. 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
2013 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 spin
Coplanar,~circular orbits
From 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,

6. Initial spin energies:
rcloud M
rorbit
Mcentral

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 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

9. 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)

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 down
layer
DUgE = -DR.E. + SEfDTE + TEiDSE
The 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) 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

13. 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

14. 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

15. 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