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The Earth: Formation from Big Bang to present

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Lecture 02 The Earth: Formation from Big Bang to present Introduction to Earth Science Earth Sci 100 * So where s-waves stop tells you that there is liquid. – PowerPoint PPT presentation

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Title: The Earth: Formation from Big Bang to present


1
Introduction to Earth Science Earth Sci 100
  • Lecture 02
  • The Earth Formation from Big Bang to present

2
Outline
  1. Origin of the Universe the Big Bang
  2. Evidence for the Big Bang
  3. Earths Structure
  4. Earths Magnetic Field

3
Hubble telescope view of the black void of the
night sky. Each spot is a distant galaxy. The
visible universe contains more than 100 billion
galaxies. Each galaxy is made up of up to 300
billion stars.
How did it all come to be?
  • R. Williams (ST Scl)-NASA

4
1. Origin of the Universe The Big Bang
  • All matter and energy was packed into a single
    dense point
  • The point exploded 14 billion years ago gt THE
    BIG BANG
  • A model of the Universes evolution has been
    deduced

5
After the Big Bang
  • First instant
  • Hot (x1028 oC), only energy
  • 3 minutes old
  • Cooled and grew to 100 billion km
  • Nucleosynthesis
  • 5 minutes old
  • chemical bond formation (H2)

6
After the Big Bang
  • cooling and expansion
  • nebulae formation (gas cloud patches)
  • centers of high gravity and began to grow, build
    heat, and spin forming protostars (200 my)
  • star ignites (true star) (800 my) and stellar
    nucleosynthesis
  • No fuel star dies (supernova explosions)
  • Next generation stars incorporate stellar
    elements and form sequentially heavier elements
    (today 92 natural elements)
  • Stream of atoms emitted from star is stellar wind

7
Fig. 1.08
  • Nebulae
  • (Hubble telescope)
  • Gas clumps form nebulae (clouds). Stars are
    forming at the top of the nebula. Already formed
    stars light up the nebula from behind.

8
p.16-17a
Formation of Solar System and Earth
The nebula condenses into a swirling disc, with a
central ball surrounded by rings.
A nebula forms from hydrogen and helium left from
the big bang
9
The ball at the center grows dense and hot enough
for fusion reactions to begin. It becomes the
Sun. Dust condenses in the rings.
Dust particles collide and stick together,
forming planetesimals.
10
Planetesimals grow by continuous collisions, and
an irregularly shaped proto-Earth develops. The
interior heats up and becomes soft.
Gravity reshapes the proto-Earth into a sphere.
The interior of the Earth differentiates
11
Soon after Earth forms, a small planet collides
with it, blasting debris that forms a ring around
the Earth.
The Moon forms from the ring of debris.
12
Eventually, the atmosphere develops from volcanic
gases. When the Earth becomes cool enough,
moisture condenses and rains to create the oceans.
13
Our Solar System
  • Formed 4.5 billion years ago
  • Planets orbit the sun
  • Moons orbit planets
  • Includes asteroid belt
  • 99.8 of solar system mass is in the sun
  • 99.5 of non-solar mass is in Jupiter

14
2. Evidence for the Big Bang How do we know the
universe formed this way?
  • Cosmic Background radiation
  • Predicted by Big Bang theory
  • Measured in the early 60s
  • Evidence for an expanding Universe
  • ALL galaxies are red-light shifted

15
Doppler effect (listen to animation)
  • Motion compresses waves
  • Higher frequency (pitch) as object moves towards
    you
  • Lower frequency (pitch) as the object moves away

16
Distant galaxies emit light
So objects moving away from Earth are red-light
shifted And objects moving towards Earth are
blue-light shifted ALL distant galaxies are
red-light shifted
17
Galaxies in the Press
http//www.nature.com/nature/journal/v443/n7108/fu
ll/443128a.html
18
Dr. Grottoli at CalTech observatory Mauna Loa, HI
13 telescopes on top of Mauna Loa, pointing
skyward, searching the universe
19
Geologic Time
Hominids (4-8 my)
Dinosaur Extinction (65 my)
Mammals (200 my) (Pangea)
Trilobite and Marine extinction (245my)
Eukaryotes ( single celled) (organelles)
Multi-celled (550-670 my)
Prokaryotes (single celled) (no organelles)
Earth Formed
Present
1.5 by
4.5 by
3.5 by
2.5 by
0.5 by
Oldest Continental Crustal plate (3.9 by)
Oldest Ocean Crustal plate (200 my)
Time
20
3. Earths Structure
21
Earths Structure
Structure Structure Chemical Composition Physical Composition
Crust Oceanic Basalt O2, Si, Mg, Fe Lithosphere (cool, rigid)
Crust Continental Granite O2, Si, Al Lithosphere (cool, rigid)
Mantle Uppermost O2, Fe, Mg, Si Lithosphere (cool, rigid)
Mantle Asthenosphere O2, Fe, Mg, Si Asthenosphere (hot, flowing)
Mantle Mantle O2, Fe, Mg, Si Mantle (hotter, denser)
Core Outer Fe, Ni Outer (hottest, viscous liquid, 4x denser than crust)
Core Inner Fe, Ni Inner (hottest, solid, 6x denser than crust)
Earths Core 5,500oC
22
  • Where does the heat within Earths layers come
    from?
  • radioactive decay
  • This heat travels in convection currents in the
    mantle (which creates flow and moves the crustal
    plates)

23
Earths Interior
  • Oceanic Crust
  • 0.099 of Earths mass, 10 km (6 miles)
  • Continental Crust
  • 0.374 of Earths mass, 70 km (44 miles)
  • Mantle
  • 67 of Earths mass, 2880 km (1800 miles)
  • Outer core
  • 30.8 of Earths mass, 2260 km (1413 miles)
  • Inner core
  • 1.7 of Earths mass, 1220 km (762 miles)
  • (Total Radius of Earth 6371 km or 3981 miles)

24
Determining the structure and composition of the
Earths interior
  1. Drill holes (12km)
  2. Density of Earth
  3. Meteorites
  4. Experiments with rocks
  5. Deep rocks brought to the surface
  6. Seismic waves

25
  • Density of Earth
  • calculate MASS of Earth from its gravitational
    influence on other planets and moon
  • Can calculate the VOLUME of Earth
  • This gives a DENSITY (Mass/Volume) of
  • 5.5 g/cm3
  • Water 1 g/cm3 Gold 19.3 g/cm3

26
  • Meteorites
  • Meteorites formed the Earth initially
  • Therefore meteorites and Earth should have the
    same BULK COMPOSITION
  • Planetesimals differentiated too, just like the
    Earth, so different types of meteorites
    correspond to different parts of the Earth

27
Stony Meteorites gt Earths Crust
Stony-Iron Meteroites gt Earths Mantle
Iron Meteorites gt Earths Core
28
  • Experiments with rocks
  • Pressure and Temperature increase with depth in
    the Earth
  • Different minerals are stable at different
    pressure and temperatures
  • Properties at these pressures and temperatures
    (melting? flowing?) are used to make models

29
  • Deep rocks brought to the surface
  • Let us see the upper mantle (we think)
  • but NOT the core or lower mantle

Kimberlite pipes in S. Africa
Ophiolites (Cyprus)
30
  • Seismic Waves
  • Generated by Earthquakes
  • Speed depends on properties of material the wave
    is passing through
  • Denser faster
  • Less Dense slower
  • Waves diffract as density changes

31
Things to know about Seismic Waves
  • Seismic Waves trace CURVED paths through the
    earth because of refraction (density increases
    with depth)

32
Seismic Waves create an image of the Earths
interior
33
  • Things to know about Seismic Waves
  • Different types
  • P waves are COMPRESSIONAL
  • S waves cause SHEARING
  • S waves cant go through liquid!!

34
P-wave paths through the Earth
35
S-wave paths through the Earth
36
S-waves more information
  • Q Why do S-waves penetrate the Aesthenosphere if
    they do not go through liquids?
  • A because the Aesthenosphere is soft (like warm
    wax) but not liquid (like water). In s-wave
    terms, this means that they penetrate the
    aesthenosphere, but not the outer core.

37
4. Earths magnetic field
  • The Magnetic field could be generated
    electrically, by the circulation of liquid metal
    in the earths outer core
  • Circulation driven by Coriolis effect

38
Earths magnetic field
The theory has this going for it It predicts
that the magnetic and geographic poles should be
nearly the same The magnetic poles slowly
drift, depending on specific details of
convection N and S poles are arbitrary and can
switch!!
39
Earths magnetic field
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