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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
• 3557 known systems, 601 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
• 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 protoEarth
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
87Rb - 87Sr
238U - 206Pb
235U - 207Pb
232Th- 208Pb
187Re - 187Os
176Lu - 176Hf
t 1/2 = 10.6 x 1010 yrs
t 1/2 = 48.8 x 109 yrs
t 1/2 = 4.47 x 109 yrs
t 1/2 = 0.704 x 109 yrs
t 1/2 = 14.01 x 109 yrs
t 1/2 = 42.3 x 109 yrs
t 1/2 = 35.7 x 109 yrs
The Law of Radioactive Decay
1
The basic equation:
-
dN
dt
N
or -
dN
dt
½
= lN
¼
D* = Nelt - N = N(elt -1)
age of a sample (t) if we know:
time 
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*
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