ES1201_Notes

Characteristics of the Earth- Water + OxygenMARS- water locked in ice caps.... presence of water in the past CO2, N2, atmosphere,,,, VENUS- Thick atmosphere but CO2 + SO2 temperature intolerable Mercury and Moon- Dry, no atmosphere SatellitesJupiter: GANYMEDE and CALLISTOSaturn: TITANMars: Phobos and Deimos (captured from Asteroid belt)

Surface of Moon1. Highland (elevated regions): Pale coloured dense covering of Impact crater Anorthosite (rich in PLAGIOCLASE FELDSPAR 90%; 10% MAFIC MINERALS) ~ 4.4 Ga 2. Maria (depressions): Darker flatter region fewer crater BASALTIC in composition ~ 3.8-4.2 Ga {crater are due to impact of meteorites and is proportional to the age of the surface}“HADEAN”: between its formation at 4.55 Ga and the age of the earliest rocks at earth is 3.9 Ga HADEAN records are obtained from other planets and Meteorites.

HYPSOMETRIC PLOT: Histogram of topographic height over a whole planet with heights determined above or below the median surface.Hypsometric plot for Earth is Bimodal. The peak at low height - Oceans The peak at Greater heights - Continental crust VENUS has only one peak & Range of elevation is less.Seismic Waves1. P waves - (body wave, compression and dilation, sound waves)2. S waves - (body wave, motion is in perpendicular direction of wave)3. Love and Rayleigh - (confined largely to the surface of the earth and most destructive)

It is difficult to extract the density from seismic velocity alone.The velocity equation for P and S waves also other variable K and μ, so no unique solution.Density: 2600-2800 kg/m3 for continent. 2800-3000 kg/m3 for oceanic crust. Crust-mantle--boundary Mohorovicic discontinuity beneath the Moho and down to 220 km referred asLow velocity zone.2 discontinuity at 410 km and 670 km...known as Mantle transition zoneCore is distinguished from the lower mantle by the Gutenberg discontinuityD’ denotes 670-2700 kmD’’ denotes 2700-2900 km {D’’ is marked by reduced velocity gradients compared with the monotonic increase in seismic velocity through D’.}Self Compression: (equation is in the pic)The integration begins at the top of the mantle based on a density of 3200 kg/m3

The SUN Different chemical elements absorb radiation at specific wavelengths. Amount of light absorbed is proportional to the amount of an element present Relative to a nominal abundance of Silicon -- 10*6 atoms. Fe is ~10^6 times abundant in the SUN than Pb. Au and Pt are comparable to Pb. Different chemical elements gradually condensed according to their individual volatilities. In a very low Pressure condition of nebula, difference in their boiling points becomes important. Meteorites Mostly derived from asteroid belt. Resulted from gravitational disturbances caused by Jupiter, perturbing the orbits of individual asteroids and causing repeated violent collisions that resulted in further fragmentation rather than accretion. Classifications of Meteorites: 1. Stony meteorites -- (dominant of silicate minerals) 95% of all known meteorite subdivided into chondrites (chondrules) and achondrites “Differentiated” 2. Iron meteorites -- (composed of metallic iron) “Differentiated” 3. Stony-iron meteorites -- (hybrid of the other two){“Differentiated” - Enrichment of Fe and Ni due to removal of some or all of the silicate minerals}Achondrites- 10% of all stony meteorite. reminiscent of terrestrial Igneous rocks. Chondrites-1. Ordinary chondrites- most abundant type2. Enstatite (or E-) chondrites- rich in Enstatite (MgSiO3)3. Carbonaceous (or C-) chondrites- carbon rich organic compounds in addition to silicates minerals.{Again ordinary chondrites are subdivided according to their iron contents and their oxidation state}

The correlation for most elements is very good-Li and B are depleted in the solar compositions relative to C-chondrites -- as they are used up in nuclear fusion reactions in the SUN.C and N are relatively depleted in C-chondrites -- They are amongst the most volatile elements.Core -- dense alloy of Iron and NickelMantle -- silicates composition- achondrite-rich in Mg. (Mantle is heterogeneous)

xenoliths -- green colour contrast with the grey black colour of the host volcanic rocks. Accidental fragments of rocks. Peridotites -- rich in minerals olivine and pyroxene silicates rich in magnesium and iron. density 3200 kg m−3 Ophiolites -- obducted oceanic crust. sedimentary rocks overlie rocks of basaltic composition, overlie peridotite. {Basaltic magma is derived from the mantle by a process known as partial melting}{Earth has lost a greater proportion of its volatile components compared with meteorites}

Siderophiles -- found in the metallic phase of a natural system. 2.0 < E < 2.4 most readily form metallic bonds. lithophiles -- elements that preferentially bond with oxygen, especially in silicate or oxide structures atmophiles- subgroup of lithophile elements that tend to be gaseous at the Earth’s surface, notably H, C, N, O and the noble gases E <1.6 forming positive ions that bond with negative oxygen ions. Chalcophiles -- elements that frequently occur bound with sulfur 1.6 < E < 2.0 readily form covalent bonds with elements such as S.

{The convention is for the numerator (Ci ) to be allocated to the liquid a and Ci the denominator (b ) to be allocated to the solid b}A lithophile element will have a D <1A siderophile element will have a D >1in these systems elements that partition into a solid phase (D ≥1) -- compatible.whereas those that are excluded and concentrate in the silicate liquid (D <1) -- incompatible.

The Earth’s core The mismatch between the curves for the core and pure iron requires the core to include other elements that reduce its overall density. siderophile elements have atomic masses, and hence densities, either similar to or even greater than that of iron. Si, is depleted by 10% in the mantle. Si is siderophile at high pressure. S is a volatile element and so may have lost from the Earth before the core formed. O is highly electronegative and suggesting a lithophile behaviour. The mantle contains abundant oxygen bound in silicates that dissociate into dense oxide phases in the deep mantle, and a variety of reactions between these oxides and oxygen-free molten iron have been suggested, all of which lead to the production of FeO (wüstite).

The magnetic field It is thought to be related to an interaction between the Earth’s rotation and convection within the outer core that, in turn, is driven by a combination of solidification of the inner core and secular cooling. Compositional convection caused by crystallization of the inner core also involves cooling of the core. However, the estimated cooling rate of the core is too great for the core to maintain heat for 3.8 Ga, and suggests that the inner core cannot be older than about 1 Ga.

The Earth’s crust: continents and oceansThe Conrad discontinuity -- 15 km depth increase in seismic velocities separates the upper crust from the lower crust Upper Crust -- Granodiorite (granite containing plagioclase and alkali feldspar 1:1 & 20% quartz)Lower Crust -- Granulites (etamorphic rocks that have been subjected to high pressures and temperatures such that they have lost most of their volatile components (largely water) and their mineralogy is dominated by plagioclase feldspar, pyroxenes and garnets, which give the lower crust its higher density){When a load is applied to the Earth’s surface, the lithosphere subsides into the underlying asthenosphere by contrast, when the load is removed the lithosphere rises again}

Differentiation is the process by which planets develop concentric layering, with zones that differ in their chemical and mineralogical compositions.Partial Melting -- When a rock is heated, different minerals within the rock will melt at different temperatures.Incompatible elements are partitioned into the melt more readily than compatible elements (element partitioning) is the principal mechanism by which incompatible elements first become concentrated into the melt.Heat sourcesPrimordial heat sources --- hose associated with accretion, collision and core formation.Tidal and radiogenic heating processes --- can operate long after the planet has been formed.Upon hitting the Earth, if all the kinetic energy of motion is converted into heat, then the increase in temperature, ΔT,ΔT = mv^2/2(m + M)Cwhere the body (of mass m) impacts the Earth (of mass M) and C is the specific heat capacity of Earth material.Core formation: If the Earth went through an early molten phase, allowing the metals and silicates to separate, then the ‘falling inwards’ of the nickel-iron rich fraction to form the core would have released potential energy --- converted first to kinetic energy and then into thermal energy.

Heat transfer within the EarthConduction -- Convection -- nvolves the movement of hot material from regions that are hotter to those that are cooler and the return of cool material to warmer regions.Advection -- when molten material (magma) moves up through fractures in the lithosphere and remains there.{The mantle can also flow when subject to temperature differences in a process known as solid-state convection and, whilst rates may be no more than a few centimetres per year, it is the most efficient form of heat transfer within all but the outermost part of the mantle}Chondrules -- millimetre-sized spherical droplets. age 4564.0±1.2 Ma Calcium and Aluminium rich Inclusions (CAIs) -- centimetre-sized and consist of the first minerals to condense at equilibrium from a gas of solar composition. age4567.2 ±0.6 Ma {the Rb/Sr fractionation may relate to the loss of a volatile phase; the age indicates when the Rb/Sr ratio in ordinary chondrites was last disturbed}

Dihedral angle, θ The dihedral angle is that formed by the liquid in contact with two solid grains, which in the case of the mantle will be silicate or oxide grains.If θ is <60°: the melt will fill channels between the solid grains. form an interconnecting network. melts will be isolated at grain corners, creating an impermeable silicate framework through which metallic melts cannot segregate. For this reason core formation is thought by many to occur only after the silicate framework has broken down after extensive silicate melting (>40%). A Crystal Mush: At these high degrees of melting the grain boundary framework will no longer be interlocked, but rather crystals will be floating in a silicate liquid.If θ is >60°: melt is confined to pockets at grain corners. cannot easily move, unless the melt fraction is greater than 10%.

Consequence of core–mantle separation-- metal- loving siderophile elements would be strongly partitioned into the metallic core.Low T–P metal silicate distribution coefficients for highly siderophile elements -- 10^–7 and 10^–15. The failure of low-temperature, low-pressure metal/silicate equilibration models to explain the siderophile excess inspired a number of alternative models,the heterogeneous accretion or ‘late veneer’ model in which core formation effectively strips out all the siderophile elements from the mantle, which are subsequently raised to the observed values by another process. Ni and Co are present in proportions that are close to chondritic, i.e. both at ~0.1 chondrite. The chondritic ratio of Ni t: Co in the mantle requires the ratio of the two partition coefficients DNi/DCo =1.1. occurs at a pressure of about 28 Gpa equivalent to a depth of 900–100 km implying high temperature and pressure metal–silicate equilibration and core segregation.