Memorial for Columbia Astronauts

1. Memorial for Columbia Astronauts • “This cause of exploration and discovery is not an option we choose. It is a desire written in the human heart. We are that part of creation which seeks to understand all creation. We find the best among us, send them forth into unmapped darkness, and pray they will return.“ --- President Bush Iain Clark, son of Laurel Clark comforted by his father

2. Origin of Earth Lecture Nine, Feb. 5, 2003

3. Course Project • Topic of your choosing related to class. • Proposal (1-2 pages) Feb. 14, 2003. • Project background (3-5 pages) Mar. 28, 2003. • Project (10 pages) April 25, 2003.

4. Project • Almost any topic of interest to you and related to the class is possible. • Try and discuss as much of the science, covered in class, as possible. • Example of a project: “The Movie 2001 and The Evolution of Man”, by C Horowitz. See paper copy or class web site. You should read this paper! Note, how it discusses the movie “2001 A Space Odyssey” in terms of many of the topics covered in class.

5. Ideas for Projects • Big Bang/ creation of Universe. • Supernovae, neutron stars, and or black holes. • Impacts of comets and asteroids. • Death of dinosaurs (See for example, “T.Rex and the crater of doom” by L. Alvarez). • Impact of Shoemaker Levy 9 with Jupiter (See for example, “Impact Jupiter” by D. Levy) • Present day impact threat.

6. Project Ideas Continued • Mars • Robotic exploration • Manned mission (See for example, “The Case For Mars”, R. Zubrin) • Colonization or terrafarming (See text) • Discuss Science in a Science Fiction Story. • 2001, 2010… by A. C. Clark • “Andromeda Strain” by M. Crichton • “Red, (Green, Blue) Mars” by K. S. Robinson • Lots and Lots to chose from… • Space exploration

7. Ideas Continued • Origin of Life • Extrasolar planets (see for example, “Worlds Unnumbered” by D. Goldsmith) • Interstellar Flight and Colonization. • SETI • …

8. Alchemy of The Heavens • Origin of the chemical elements. • Chemical element has atomic number Z (number of electrons orbiting nucleus). • Big Bang Nucleosynthesis: after the first 3 min. Universe was about 25% He and 75% H and little heavier elements. • First generation stars had no heavy elements for rocky planets or life. • First generation stars make elements in core. • New elements released into interstellar medium when star dies either as planetary nebula or supernova.

9. Life of a Star • Birth: collapse of gas cloud forms protostar. • Main sequence: center of star becomes hot enough to burn Hydrogen into Helium. Our Sun will be on main sequence for 10 billion years. • Red Giant: Outer part of star expands and cools. Core contracts and starts to burn He into Carbon and other heavier elements. • Star dies: either as a planetary nebula (low mass star) or as a supernova (high mass star).

10. Supernovae • Gigantic stellar explosions. • Eject new chemical elements into space. • Make neutron stars and black holes. • Accelerate cosmic rays (energetic particles constantly hitting Earth’s atmosphere from space). • Shock waves can help gas clouds to collapse and form new stars. • Deadly to life (within say ~1-300 light years???)

11. Origin of Earth • Why are there planets? To conserve angular momentum (amount of spin). • (Linear) momentum is mass times velocity. • Angular momentum is momentum times distance from rotation axis. • Think of an ice skater in a spin. With her arms apart she spins slowly (her hands have a small momentum times a large distance from her rotation axis). As she brings her hands in she spins much faster. Angular momentum is conserved. Because her hands are nearer the rotation axis they must have a higher momentum and so she spins faster.

12. Collapse of Primitive Solar Nebula • Very extended gas cloud has, in general, a very small but nonzero rotation. • As the cloud collapses the conservation of angular momentum causes it to rotate faster. • Gas cloud can more easily collapse along rotation axis so a round cloud flattens into a disk.

13. False color image of disk around Beta Pict.

14. Formation of Solar System • The center of the disk collapses to form a star. • While the rest of the disk forms a system of planets. • Planets and star formed at same time. • All planets are expected to orbit around the star in the same direction.

15. Formation of Star and Planets

16. Planets versus Double Stars • Two ways to conserve angular momentum: • Form a single star with planets. • Form two or more stars orbiting each other (indeed many stars are observed to be in binary or multiple star systems, for example the nearest star Alpha Cent. is a triple star system) • Expect planets to be common.

17. Earth Formed Hot • Large impacts continued. • Heat of formation melted rocks. • Dense Iron and other materials sank to form core of Earth leaving mantle depleted in dense elements. • Radioactive decay of Uranium, Thorium and Potassium helped to heat interior of earth. • Core cools by convection. Hot material rises and cold material sinks. This leads to rotating motions which carry heat away from core.

18. The Earth Cools by Convection • Hot material near the core expands and becomes less dense. It then rises. As it cools it becomes denser and sinks back to the core. • This rotary motion transports heat from the core. • These motions can power plate tectonics where large plates move carrying many surface features with them. • Convective currents also generate earth’s magnetic field. Core

19. Plate Tectonics

20. Formation of New Crust • As plates move apart, the Atlantic ocean is getting wider and new crust is forming in mid ocean. • Age of crust:

21. Evolving Earth Crucial for Life • Magnetic field shields cosmic rays (radiation) from space. • Early atmosphere rich in CO2. • Greenhouse effect of CO2 very important for Earth temperature. Gases trap Sun’s heat and keep it from being reradiated back into space. CO2 is transparent to visible light but absorbs infrared radiation. • Without greenhouse effect, Earth would be some 35 C colder (average temp. below -20 C instead of +12 C) and a frozen ice ball.

22. Earth’s Thermostat • Amount of CO2 in atmosphere controlled by absorption to make carbonate rocks or out-gassing from volcanoes. • This changes greenhouse effect and Earth’s temperature. • Earth’s temperature has been remarkably stable over its history despite an increase in the Sun’s output. • There must have been more CO2 at early times and this somehow decreased in a way that compensated the increase in the Sun’s output.

23. We don’t understand this Thermostat • We don’t understand many of the mechanisms which regulate CO2. • How much more CO2 will lead to a runaway greenhouse effect such as what happened to Venus? • What will the ultimate effect of human produced CO2 be (global warming)? • How close did Earth come to losing CO2 and going into a permanent global ice age (“snowball earth”)?

24. Venus is Hot as Hell • Atmosphere is 90 times thicker then Earth and mostly CO2. • Greenhouse effect raises temp. by 400 C to about 470 C (hot enough to melt lead). • Not a likely place for life.

25. Mars was once Warmer and Wetter • In the past, Mars atmosphere had much more CO2. • This allowed greenhouse effect to raise temp. above 0 C. • Mars has since lost most of its atmosphere for unknown reasons, perhaps absorption in rocks.

26. Formation of Earth • Planets and Stars from together from collapse of rotating gas cloud. • Sun and planets of same age. • Planets all orbit Sun in same direction. • Earth formed hot. Rocks melted. • Denser material such as Iron sunk to center and formed Earth’s Core. • Radioactive decay continues to heat core.

27. Earth is Geologically Alive. • We are lucky that Earth’s core is still hot and this heat flow drives convection, plate tectonics and generates magnetic field. • Plate tectonics may help regulate CO2 in atmosphere. • Note, no other planet in solar system appears to have plate tectonics. • Earth’s temp. remained remarkably stable despite warming Sun. • Timeline: Big Bang 13 Bya, creation of chemical elements 12-5 Bya, formation of Earth 4.6 Bya, formation of Moon in Big Whack 4.5 Bya, Large impact basins on Moon 3.8 Bya, Origin of life 3.8 Bya.

28. For next time • Read chap. 4 of Jakosky about the earliest life and read “Vital Dust", pages 1-23 in course packet about origin of life. • Think about your course project. Read sample project “The Movie 2001 and the Evolution of Man”. Proposal (1-2 pages) due Feb. 14, 2003. • Next lecture, Friday. Feb 7, 2003, “Origin of Life”.