Transcript Olivia
EPSC 644 Team 3: Olivia ● Accretion of Earth from solar nebula ● Geophysical differentiation of Earth ● Moon formation ● Magnetics and the core geodynamo ● Heat budget of our planet Accretion The Crab Nebula © NASA The Solar Nebula (painting) © W.K. Hartmann PSI Physical differentiation ● Fe: 35%; O: 30%; Si: 15%; Mg: 13%: olivine! ● Scenarios... – – ● Earth forms cool and homogeneous, heats up due to radiogenic element decay and so differentiates... Earth forms from already partially differentiated planetesmals..., heats up and continues further differentiations.... Physical differentiation of Earth... – – Where is all the Fe? It has sunk into the core! Essentially density driven: denser compositions sink to the deepest interior. The “Big Whack” The Moon forms... © W.K. Hartmann PSI The scenario “fits” data... ● ● ● ● The Earth has a large iron core, but the moon does not. Fe had already largely sunk into core. Earth has a mean density of 5.5 gm/cm3; moon, 3.3 gm/cm3. Moon has less iron. The moon has same 18O, 17O, 16O composition as the Earth. Mars and the asteroids differ. Earth's Moon is “large”. The other terrestrial planets have only small moons or none at all. Archean paleomagnetics Valet, J-P., Time variations in paleomagnetic intensity, Reviews of Geophysics, 41-1, 2003. Geodynamo Core http://geomag.usgs.gov/movies/movies/index.php?type=corefield&for mat=flash Heat budget... ● The interior of the Earth is hot! Hot hot? – – – – ~ 1500K at base of lithosphere ~ 2800K – 3400K at base of mantle ~ 5000K at inner-core boundary ~ 5500K at centre Heat again... Why hot? Rapid heating following a cold accretion by decay of short-lived radionuclei (26Al) – Residual gravitational potential energy from original accretion (to ~40%). – The geodynamo requires a heat drive. ● Core freezing, chemical differentiation and 40K or U/Th (fission?) in the inner core. – The mantle is convecting. ● Internal heating from K, U, Th decay as well as from the core beneath. –