Lecture 02 The Earth: Formation from Big Bang to present

1. Introduction to Earth ScienceEarth Sci 100 Lecture 02 The Earth: Formation from Big Bang to present

2. Outline • Origin of the Universe: the Big Bang • Evidence for the Big Bang • Earth’s Structure • Earth’s 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 => THE BIG BANG • A model of the Universe’s 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. Formation of Solar System and Earth p.16-17a 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 60’s • 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/full/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. Earth’s Structure

21. Earth’s Structure Earth’s Core ~5,500oC

22. 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)

23. 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)

24. Determining the structure and composition of the Earth’s interior • Drill holes (12km) • Density of Earth • Meteorites • Experiments with rocks • Deep rocks brought to the surface • 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 => Earth’s Crust Stony-Iron Meteroites => Earth’s Mantle Iron Meteorites => Earth’s 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 Earth’s interior

33. Things to know about Seismic Waves • Different types: • P waves are COMPRESSIONAL • S waves cause SHEARING • S waves can’t go through liquid!!

34. P-wave paths through the Earth

35. S-wave paths through the Earth

36. S-wavesmore 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. 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

38. 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!!

39. Earth’s magnetic field