Transcript Overheads for origin of earth

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.
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 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
• More realistic calculations with multiple
impacts lead to slightly longer times for
core formation
Solar Systems Form by Accretion