Anne M. Hofmeister and Robert E. Criss

An Alternative view of Earth’s Beginnings

Anne M. Hofmeister and Robert E. Criss

Geophysics•Heat transferGeochemistry•Meteorite chemical composition•Isotopic dataThermodynamicsAstronomy•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.

An Alternative view of Earth’s Beginnings

Earth’s current state stems from conditions of formation and differentiation which we infer from conservation laws and physical evidence

~Upright spinCoplanar,~circular orbits

From NASA andhttp://test.glossopedia.org/solar-system

/

1024

1026

1028

1030

1032

1034

1036

1038

1024 1026 1028 1030 1032 1034 1036 1038

REspin

,

kJ

-Ug = -U

g, kJ

Current spin

Jupiter

NeptuneUranus

Saturn

braking

Sun's spinnow

y = 7.1947x10-11 x1.225

1:1

Earth

Mars

R

MU g

2G

5

3

R.E. = ½I2

Current solar system energies depend strongly on

self-gravitational potential

1028

1030

1032

1034

1036

1038

1028 1030 1032 1034 1036 1038

REspin

(kJ)

-Ug = -U

g (kJ)

Current spin

Jupiter

Neptune

Uranus

Saturn

protoSun initial spin

braking

Sun's spinnow

y = 7.1947x10-11 x1.225

M35

M50

Initial spin energies:

M50: Irwin J. et al. (2009) MNRAS, 392, 1456-1466

M35: Meibom S., Mathieu R. D., Stassun K. G. (2009) ApJ, 695, 679-694

central

2

orbit

cloud

M

M

r

r

1028

1030

1032

1034

1036

1038

1028 1030 1032 1034 1036 1038

REspin

(kJ)

-Ug = -U

g (kJ)

Current spin

Jupiter

Neptune

Uranus

Saturn

calculated from maximum cloud size

protoSun initial spin

braking

Sun's spinnow

y = 7.1947x10-11 x1.225

Sumspin+orbit

M35

calculated from prograde satellite orbits

M50

Initial spin energies:

rorbit

Mcentral

rcloud

M

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)

Wrong about star light

Cp is negative

Data and thermodynamics show that gravitational contraction cannot cause heat

production

Kelvin assumed Ug = positive = total energy

The heating idea predates nuclear reactions or fast-spinning stars

If Ug = total positive E

Influx of heat (light) can cool the nebula below 0 K

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 Ug = positive = total energy

The heating idea predates nuclear reactions or fast-spinning stars

If Ug = total positive E

Influx of heat (light) can cool the nebula below 0 K

-Ug R.E.

0

5000

10000

15000

20000

3600 4000 4400 4800 5200 5600 6000 6400

T, K

Radius, km

to 31520 K

homogeneous globe (b=0)

b=3485 km

b=5700 km

b=5970 km

b=6270 km

9.8 K/km

b a

k = 6 W/(m-K)Q =30 TW

Forming layers wherein radioactive isotopes rise upwards greatly cooled the Earth

A globe with homogeneously distributed radioactive elements would be astronomically hot

UgE = -R.E. + SEfTE + TEiSE

The signs of the terms show that TE 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

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

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, CO2, H2O)Silicates (enstatite)Oxides (CAI’s)Metal (Fe)

depth

ghot particlesU, Thmelts, gases

Earth’s gross composition can be inferred from its radioactive emissions and meteorite data

0

200

400

600

800

1000

1200

0 10 20 30 40

Moon

H

LLL

EH

EL

Silicates

K p

pm

U ppb

10 TW

30 TW

50 TW

K/U

=104

Metals

C1

Earth

Refractories

20 TW

40 TW

60 TW

?

BOE

Silicates Chondrites

CAIsCalcium Aluminum Inclusions

Oxygen isotopes of meteorites require

two reservoirs

Meteorite reservoirs have similar mass proportions as zones in the present Earth

Refractories~3.8 g/cm3

Lower Mantle30% by massO, Ca, Al, Mg, SiCSome Fe, Ti

Metals~7 g/cm3

Silicates<3 g/cm3

Crust + Upper mantle + Transition zone 17% 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.

Core50% by massFe,Ni,C,S,N

• Gravitational contraction produces spin; whereas accretionary and core heating are inconsequential

• Earth 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

Summary