Nancy Van Wagoner, Acadia University Origin of Earth

Nancy Van Wagoner, Acadia University Perspective in Space u u We live on planet Earth u u solar system u u Milky way galaxy u u universe

Nancy Van Wagoner, Acadia University Origin of Universe u u Age? perhaps 8-10 billion years u u Big Bang Theory u u At that time all matter that formed the sun, formed the earth and us. Remember matter changes form but is not destroyed.

Nancy Van Wagoner, Acadia University u u The universe was mostly light elements F F Hydrogen 75% atomic weight 1 F F Helium 25% atomic weight 2

Nancy Van Wagoner, Acadia University Where did heavier elements come from? u u thermonuclear reactions in exploding stars called supernova. u u For more information Supernova--Death of a Star, National Geographic, v.173, n.5, p.618, 1988.

u u It is postulated that in this expanding universe about 6 billion years ago, a supernova exploded. Gas and dust began to spin which was caused by rotation of the galaxy. u u Gravity concentrated most of the mass at the centre which would become the sun and producing a solar nebula. sun dust and gas fig. 1.8, Thompson and Turk

u Planets condensed from material in the nebula but, because the nebula was stratified with respect to temperature and composition the planets are different in composition. sun Mercury Venus Earth Mars Asteroid Belt Jupiter Fe, Al, CaIce (H,C,N) Hot Cold Earth-like Planets Jovian Planets

Nancy Van Wagoner, Acadia University Look more closely at Earth. u u Earth at one time was a homogeneous spinning and contractng body Fe Mg Al Ca Si K Na Si Ca Al

Nancy Van Wagoner, Acadia University u u The protoplanet grew hotter until it reached the melting temperature of iron. – –Melting event – –The sources of heat were from F F - meteor impact F F - radioactive decay F F - gravitational contraction

Nancy Van Wagoner, Acadia University Result of Melting event u u - lighter materials rose to the surface u u - heavier ones sank to the core u u The result: compositional and density stratified the Earth.

Nancy Van Wagoner, Acadia University Composition of Earth and Crust

Nancy Van Wagoner, Acadia University Periodic Table Exercise u notice order of elements u Elements expected near centre: u Elements expected near surface: u The Ur/Th surprise –Ur and Th became concentrated in the crust because they are about the same size and charge as some of the lighter elements (K,Na) and therefore can replace these elements in the crystal structure of minerals.

Nancy Van Wagoner, Acadia University Layers of Earth

Nancy Van Wagoner, Acadia University Inner Core u radius = 1216 km u composition = Iron, Nickel +/- silicon, carbon u state = solid 1216 km

Nancy Van Wagoner, Acadia University Outer Core u thickness 2270 km u Composition = same as inner core inner core u state = liquid u density = 9-15 gm/cc

Nancy Van Wagoner, Acadia University Mantle u thickness = 2885 km u comp = iron and magnesium silicates and oxides u density = 4-7 gm/cc

Nancy Van Wagoner, Acadia University Layers of the Mantle u lithosphere = crust + upper mantle –cool, rigid, brittle u asthenosphere = partially molten –hot, weak, plastic u mesophere = solid but hot –due to high pressure 100km 350 km to base of mantle

crust oceanic crust rigid mantle continental crust km 5-10 km oceanic lithosphere continental lithosphere

Nancy Van Wagoner, Acadia University Oceanic Crust u dense rocks = 3.2 gm/cc u basalt (iron and magnesium silicates) u relatively thin

Nancy Van Wagoner, Acadia University Continental Crust u less dense = 2.8 gm/cc u granitic Si, Al u thicker

Nancy Van Wagoner, Acadia University Why are there Continents and Ocean Basins ?

Nancy Van Wagoner, Acadia University Plate Tectonics u Lithosphere broken into lithospheric plates u Move with respect to each other u rate = cm/yr.

Nancy Van Wagoner, Acadia University Plate Margins u - Divergent: spreading centre; new crust created u - Convergent: subduction; collision u - Transform: earthquakes - San Andres fault