Presentation on theme: "Lecture 02 The Earth: Formation from Big Bang to present Introduction to Earth Science Earth Sci 100."— Presentation transcript:
Lecture 02 The Earth: Formation from Big Bang to present Introduction to Earth Science Earth Sci 100
Outline 1.Origin of the Universe: the Big Bang 2.Evidence for the Big Bang 3.Earth’s Structure 4.Earth’s Magnetic Field
R. Williams (ST Scl)-NASA 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?
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 => THE BIG BANG A model of the Universe’s evolution has been deduced
After the Big Bang First instant: –Hot (x10 28 o C), only energy 3 minutes old: –Cooled and grew to 100 billion km –Nucleosynthesis 5 minutes old: –chemical bond formation (H 2 )
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
Fig 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.
p.16-17a A nebula forms from hydrogen and helium left from the big bang The nebula condenses into a swirling disc, with a central ball surrounded by rings. Formation of Solar System and Earth
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.
Gravity reshapes the proto-Earth into a sphere. The interior of the Earth differentiates Planetesimals grow by continuous collisions, and an irregularly shaped proto-Earth develops. The interior heats up and becomes soft.
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.
Eventually, the atmosphere develops from volcanic gases. When the Earth becomes cool enough, moisture condenses and rains to create the oceans.
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
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 60’s Evidence for an expanding Universe… ALL galaxies are red-light shifted
Doppler effect (listen to animation) Motion compresses waves –Higher frequency (pitch) as object moves towards you –Lower frequency (pitch) as the object moves away
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
Galaxies in the Press
Dr. Grottoli at CalTech observatory Mauna Loa, HI 13 telescopes on top of Mauna Loa, pointing skyward, searching the universe
Earth Formed Prokaryotes (single celled) (no organelles) Eukaryotes ( single celled) (organelles) Multi-celled ( my) Hominids (4-8 my) Dinosaur Extinction (65 my) Mammals (200 my) (Pangea) Present 4.5 by 3.5 by2.5 by 1.5 by 0.5 by Time Oldest Ocean Crustal plate (200 my) Oldest Continental Crustal plate (3.9 by) Geologic Time Trilobite and Marine extinction (245my)
3. Earth’s Structure
Earth’s Structure Structure Chemical Composition Physical Composition Crust OceanicBasalt: O 2, Si, Mg, Fe Lithosphere (cool, rigid) ContinentalGranite: O 2, Si, Al Mantle Uppermost O 2, Fe, Mg, Si Asthenosphere Asthenosphere (hot, flowing) MantleMantle (hotter, denser) Core Outer Fe, Ni Outer (hottest, viscous liquid, 4x denser than crust) Inner Inner (hottest, solid, 6x denser than crust) Earth’s Core ~5,500 o C
Where does the heat within Earth’s layers come from? radioactive decay This heat travels in convection currents in the mantle (which creates flow and moves the crustal plates)
Earth’s Interior Oceanic Crust –0.099% of Earth’s mass, 10 km (6 miles) Continental Crust –0.374% of Earth’s mass, 70 km (44 miles) Mantle –67% of Earth’s mass, 2880 km (1800 miles) Outer core –30.8% of Earth’s mass, 2260 km (1413 miles) Inner core –1.7% of Earth’s mass, 1220 km (762 miles) (Total Radius of Earth = 6371 km or 3981 miles)
Determining the structure and composition of the Earth’s interior i.Drill holes (12km) ii.Density of Earth iii.Meteorites iv.Experiments with rocks v.Deep rocks brought to the surface vi.Seismic waves
ii.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/cm3Gold = 19.3 g/cm3
iii.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
iv.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
v.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)
vi.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
Things to know about Seismic Waves Seismic Waves trace CURVED paths through the earth because of refraction (density increases with depth…)
Seismic Waves create an image of the Earth’s interior
Things to know about Seismic Waves -Different types: -P waves are COM P RESSIONAL -S waves cause S HEARING -S waves can’t go through liquid!!
P-wave paths through the Earth
S-wave paths through the Earth
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.
4. Earth’s magnetic field The Magnetic field could be generated electrically, by the circulation of liquid metal in the earth’s outer core Circulation driven by Coriolis effect
Earth’s 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!!