nancy van wagoner, acadia university origin of earth

Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University

Origin of Earth


Perspective in Space

We live on planet Earth solar system Milky way galaxy universe


Origin of Universe

Age? perhaps 8-10 billion years Big Bang Theory At that time all matter that formed the sun,

formed the earth and us. Remember matter changes form but is not destroyed.


The universe was mostly light elements Hydrogen 75% atomic weight 1 Helium 25% atomic weight 2


Where did heavier elements come from?

thermonuclear reactions in exploding stars called supernova.

For more information Supernova--Death of a Star, National Geographic, v.173, n.5, p.618, 1988.

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.

Gravity concentrated most of the mass at the centre which would become the sun and producing a solar nebula.

sundust and gas

fig. 1.8, Thompson and Turk

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.

sunMercuryVenus Earth Mars

Asteroid Belt

Jupiter

Fe, Al, Ca Ice (H,C,N)

Hot Cold

Earth-like Planets Jovian Planets


Look more closely at Earth.

Earth at one time was a homogeneous spinning and contractng body

Fe

Mg

AlCa

Si

K

NaSi

Si

Ca

Al


The protoplanet grew hotter until it reached the melting temperature of iron.– Melting event– The sources of heat were from

- meteor impact - radioactive decay - gravitational contraction


Result of Melting event

- lighter materials rose to the surface - heavier ones sank to the core The result: compositional and density

stratified the Earth.


Crust Total Earth

Fe 5.6 35O 45 28Mg 2 17Si 28 13S 0.03 2.7Ni 0.007 2.7Ca 4.2 0.61Al 8. 2 0.44Co 0.002 0.20Na 2.4 0.14Mn 0.09 0.09K 2.1 0.07Ti 0.57 0.04P 0.10 0.03Cr 0.01 0.01

Composition of Earth and Crust


Periodic Table Exercise

notice order of elementsnotice order of elements Elements expected near centre:Elements expected near centre: Elements expected near surface:Elements expected near surface: The Ur/Th surpriseThe Ur/Th surprise

– Ur and Th became concentrated in the crust because Ur and Th became concentrated in the crust because they are about the same size and charge as some of they are about the same size and charge as some of the lighter elements (K,Na) and therefore can the lighter elements (K,Na) and therefore can replace these elements in the crystal structure of replace these elements in the crystal structure of minerals.minerals.


Layers of Earth


Inner Core

radius = 1216 kmradius = 1216 km composition = composition = Iron, Nickel +/-Iron, Nickel +/-

silicon, carbonsilicon, carbon

state = solidstate = solid

1216 km


Outer Core

thickness 2270 kmthickness 2270 km Composition = same asComposition = same as

inner coreinner core state = liquidstate = liquid density = 9-15 gm/ccdensity = 9-15 gm/cc


Mantle

thickness = 2885 kmthickness = 2885 km comp = comp =

iron and magnesiumiron and magnesium

silicates and oxidessilicates and oxides density = 4-7 gm/ccdensity = 4-7 gm/cc


Layers of the Mantle

lithosphere = crust + upper mantlelithosphere = crust + upper mantle– cool, rigid, brittlecool, rigid, brittle

asthenosphere = partially asthenosphere = partially moltenmolten– hot, weak, plastichot, weak, plastic

mesophere = solid but hotmesophere = solid but hot– due to high pressuredue to high pressure

100km

350 km

to baseof mantle

crust

oceanic crust

rigid mantle

continental crust30-70 km

5-10 km

oceanic lithosphere

continentallithosphere


Oceanic Crust

dense rocks = 3.2 gm/ccdense rocks = 3.2 gm/cc basalt (iron and magnesium silicates)basalt (iron and magnesium silicates) relatively thinrelatively thin


Continental Crust

less dense = 2.8 gm/ccless dense = 2.8 gm/cc granitic Si, Al granitic Si, Al thickerthicker


Why are there Continents and Ocean Basins ?


Plate Tectonics

Lithosphere broken into lithospheric platesLithosphere broken into lithospheric plates Move with respect to each other Move with respect to each other rate = 1- 12 cm/yr.rate = 1- 12 cm/yr.


Plate Margins - Divergent: spreading centre; new crust - Divergent: spreading centre; new crust

createdcreated - Convergent: subduction; collision- Convergent: subduction; collision - Transform: earthquakes - San Andres fault- Transform: earthquakes - San Andres fault

nancy van wagoner, acadia university origin of earth

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