Post on 16-Jan-2016
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
Origin of Earth
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
Perspective in Space
We live on planet Earth solar system Milky way galaxy universe
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
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.
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
The universe was mostly light elements Hydrogen 75% atomic weight 1 Helium 25% atomic weight 2
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
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
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
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
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
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
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
Result of Melting event
- lighter materials rose to the surface - heavier ones sank to the core The result: compositional and density
stratified the Earth.
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
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
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
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.
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
Layers of Earth
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
Inner Core
radius = 1216 kmradius = 1216 km composition = composition = Iron, Nickel +/-Iron, Nickel +/-
silicon, carbonsilicon, carbon
state = solidstate = solid
1216 km
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
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
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
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
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
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
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
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
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
Continental Crust
less dense = 2.8 gm/ccless dense = 2.8 gm/cc granitic Si, Al granitic Si, Al thickerthicker
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
Why are there Continents and Ocean Basins ?
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
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.
Nancy Van Wagoner, Acadia UniversityNancy Van Wagoner, Acadia University
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