SIO224 Internal Constitution of the

EarthFundamental problem: the nature of mass and heat transfer in the mantle

and the evolution of the Earth

• Seismology:1D and 3D structure of the Earth

• Geochemistry: bulk composition of the Earth; heat production; geochemical tracers of “mantle reservoirs”

• Mineral physics: thermoelastic properties of materials at high T and P (equations of state); phase transformations; rheology of mantle materials

• Geodynamics: flow models, geoid constraints, mantle convection, effects of phase transformations and viscosity variations on convection, thermochemical convection, thermal history.

Ingredients for a unified mantle model

Origin of the solar system

Planetary migration (Nice model)

• Giant planets have migrated over time, Uranus and Neptune were closer in but migrated out after Saturn and Jupiter went into 2:1 resonance

• Jupiter also migrated slightly inward – interactions with left over material led to late heavy bombardment

• Issues with this – still being debated

Exosolar systems

• 1202 known systems, 480 known to have multiple planets (two have 7 planets)

• Some problems for standard theory: orbits not often circular and not coplanar and not all orbit in same direction!

• Maybe planetary interactions are generally more important than in our solar system

Formation of the moon

• Main problem is simulations show that moon is dominantly composed of impactor mantle but oxygen isotopes of moon and Earth are identical

• Can fix by having higher velocity impactor or make impactor more similar to proto-Earth

Meteorites and the composition of the

Earth

Timing of core/moon formation

Principles of Isotope Geology:

Conventional radiogenic isotope systematics used in geology: 147Sm - 143Nd t 1/2 = 10.6 x 1010 yrs87Rb - 87Sr t 1/2 = 48.8 x 109 yrs238U - 206Pb t 1/2 = 4.47 x 109 yrs235U - 207Pb t 1/2 = 0.704 x 109 yrs232Th- 208Pb t 1/2 = 14.01 x 109 yrs187Re - 187Os t 1/2 = 42.3 x 109 yrs176Lu - 176Hf t 1/2 = 35.7 x 109 yrs

The Law of Radioactive Decay

The basic equation:

- -dN

dtN or

dN

dt= N

# parent atoms

time

1

½

¼

D* = Net - N = N(et -1)

age of a sample (t) if we know: D* the amount of the daughter nuclide produced

N the amount of the original parent nuclide remaining

the decay constant for the system in question

(= ln 2/ t ½)

More conventionally, D(present) = Do + D*

These systematics are being used as chronometers a) model ageb) isochron age

and as petrogenetic tracers….

Hf is enriched in the silicate mantle after core formation

• More realistic calculations with multiple impacts lead to slightly longer times for core formation

Solar Systems Form by Accretion