Origin of the solar system Solar Systems Form by Accretion 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 1137 known systems, 467 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 e=(ra-rp)/(ra+rp), a=(rp+ra)/2 Meteorites and the composition of the Earth Timing of core/moon formation Principles of Isotope Geology: Conventional radiogenic isotope systematics used in geology: 147 Sm Ndt 1/2 = 10.6 x yrs 87 Rb- 87 Srt 1/2 = 48.8 x 10 9 yrs 238 U- 206 Pbt 1/2 = 4.47 x 10 9 yrs 235 U- 207 Pbt 1/2 = x 10 9 yrs 232 Th- 208 Pbt 1/2 = x 10 9 yrs 187 Re Os t 1/2 = 42.3 x 10 9 yrs 176 Lu Hft 1/2 = 35.7 x 10 9 yrs The Law of Radioactive Decay The basic equation: - - dN dt N or dN dt =N # parent atoms time 11 D* = Ne t - N = N(e t -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 ) More conventionally, D (present) = D o + D* These systematics are being used as chronometers a)model age b)isochron age and as petrogenetic tracers. Hf is enriched in the silicate mantle after core formation Major structural divisions of the Earth