SIO224 Internal Constitution of the Earth Fundamental problem: the nature of mass and heat transfer in the mantle and the evolution of the Earth

Ingredients for a unified mantle model 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.

Shear velocity -- +-1% isovelocity surfaces Includes S and SS cluster analysis data

Origin of the solar system

Solar Systems Form by Accretion Let us study the sequence in slightly more detail: The processes by which dust particles began to adhere to one another and form hierarchy of planetesimals of varying sizes are poorly understood, but it is clear that for accretion to commence, the relative velocities of dust grains had to be minimized so that they approached each other very slowly, thereby allowing surface chemical forces to cause them to adhere during gentle impacts. Dust grains began to adhere, building up a first generation of a small aggregations or planetisimals, perhaps with dimensions up to a few cm. Thus a thin, relatively dense disk of dust and small planetisimals collected quickly in the equatorial plane.

Condensation sequence: Let us step back some more: After the formation of elements in the stars, Most studies have taken the initial state to be a high T gas of solar composition and have calculated, from thermodynamic data, the sequence of solid phases that separate from the gas as T falls. Some of the results are summarized in Fig. 6.6 at total p at 10-4 bar.

Planetary migration 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

Exosolar systems 2701 known systems, 610 known to have multiple planets (two have 7 planets) On average, one planet per star and 1 in 5 Sun-like planets have an “Earth-sized” planet in the habitable zone First planets to be identified were “hot Jupiters” – now known to be not so common Some systems are not “nebular like” Maybe planetary interactions are generally more important than in our solar system

Formation of the moon

Meteorites and the composition of the Earth

Timing of core/moon formation

Conventional radiogenic isotope systematics used in geology: Principles of Isotope Geology: Conventional radiogenic isotope systematics used in geology:   147Sm - 143Nd t 1/2 = 10.6 x 1010 yrs 87Rb - 87Sr t 1/2 = 48.8 x 109 yrs 238U - 206Pb t 1/2 = 4.47 x 109 yrs 235U - 207Pb t 1/2 = 0.704 x 109 yrs 232Th- 208Pb t 1/2 = 14.01 x 109 yrs 187Re - 187Os t 1/2 = 42.3 x 109 yrs 176Lu - 176Hf t 1/2 = 35.7 x 109 yrs

The Law of Radioactive Decay The basic equation: 1 ½ ¼ - µ dN dt N or = N l # parent atoms D* = Nelt - N = N(elt -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 l the decay constant for the system in question (= ln 2/ t ½) More conventionally, D(present) = Do + D* time  Note half-life is a constant (as is decay constant)

These systematics are being used as chronometers model age isochron age and as petrogenetic tracers….

lithophile elements (oxygen, oxides, silicate minerals, Earth composition continued….. lithophile elements (oxygen, oxides, silicate minerals, Greek lithos - stone) chalcophile (sulphides, Greek khalkos=copper) siderophile (metallic, Greek sideros=iron)

Hf is enriched in the silicate mantle after core formation