Memorial for Columbia Memorial for Columbia Astronauts Astronauts

• ““This cause of exploration This cause of exploration and discovery is not an and discovery is not an option we choose. It is a option we choose. It is a desire written in the human desire written in the human heart. We are that part of heart. We are that part of creation which seeks to creation which seeks to understand all creation. We understand all creation. We find the best among us, find the best among us, send them forth into send them forth into unmapped darkness, and unmapped darkness, and pray they will return.“ pray they will return.“

--- President Bush--- President Bush

Iain Clark, son of Laurel Clark comforted by his Iain Clark, son of Laurel Clark comforted by his fatherfather

Origin of EarthOrigin of Earth

Lecture Nine, Feb. 5, 2003Lecture Nine, Feb. 5, 2003

Course ProjectCourse Project

• Topic of your choosing related to Topic of your choosing related to class.class.

• Proposal (1-2 pages) Feb. 14, 2003.Proposal (1-2 pages) Feb. 14, 2003.

• Project background (3-5 pages) Mar. Project background (3-5 pages) Mar. 28, 2003. 28, 2003.

• Project (10 pages) April 25, 2003.Project (10 pages) April 25, 2003.

ProjectProject

• Almost any topic of interest to you and Almost any topic of interest to you and related to the class is possible.related to the class is possible.

• Try and discuss as much of the science, Try and discuss as much of the science, covered in class, as possible.covered in class, as possible.

• Example of a project: “The Movie 2001 and Example of a project: “The Movie 2001 and The Evolution of Man”, by C Horowitz. See The Evolution of Man”, by C Horowitz. See paper copy or class web site. You should paper copy or class web site. You should read this paper! Note, how it discusses the read this paper! Note, how it discusses the movie “2001 A Space Odyssey” in terms of movie “2001 A Space Odyssey” in terms of many of the topics covered in class. many of the topics covered in class.

Ideas for ProjectsIdeas for Projects

• Big Bang/ creation of Universe.Big Bang/ creation of Universe.

• Supernovae, neutron stars, and or black Supernovae, neutron stars, and or black holes.holes.

• Impacts of comets and asteroids.Impacts of comets and asteroids.– Death of dinosaurs (See for example, “T.Rex Death of dinosaurs (See for example, “T.Rex

and the crater of doom” by L. Alvarez).and the crater of doom” by L. Alvarez).– Impact of Shoemaker Levy 9 with Jupiter (See Impact of Shoemaker Levy 9 with Jupiter (See

for example, “Impact Jupiter” by D. Levy)for example, “Impact Jupiter” by D. Levy)– Present day impact threat.Present day impact threat.

Project Ideas ContinuedProject Ideas Continued

• MarsMars– Robotic explorationRobotic exploration– Manned mission (See for example, “The Case Manned mission (See for example, “The Case

For Mars”, R. Zubrin)For Mars”, R. Zubrin)– Colonization or terrafarming (See text)Colonization or terrafarming (See text)

• Discuss Science in a Science Fiction Story.Discuss Science in a Science Fiction Story.– 2001, 2010… by A. C. Clark2001, 2010… by A. C. Clark– ““Andromeda Strain” by M. CrichtonAndromeda Strain” by M. Crichton– ““Red, (Green, Blue) Mars” by K. S. RobinsonRed, (Green, Blue) Mars” by K. S. Robinson– Lots and Lots to chose from…Lots and Lots to chose from…

• Space explorationSpace exploration

Ideas ContinuedIdeas Continued

• Origin of LifeOrigin of Life

• Extrasolar planets (see for example, Extrasolar planets (see for example, “Worlds Unnumbered” by D. “Worlds Unnumbered” by D. Goldsmith)Goldsmith)

• Interstellar Flight and Colonization.Interstellar Flight and Colonization.

• SETISETI

• ……

Alchemy of The HeavensAlchemy of The Heavens

• Origin of the chemical elements.Origin of the chemical elements.• Chemical element has atomic number Z (number of Chemical element has atomic number Z (number of

electrons orbiting nucleus).electrons orbiting nucleus).• Big Bang Nucleosynthesis: after the first 3 min. Big Bang Nucleosynthesis: after the first 3 min.

Universe was about 25% He and 75% H and little Universe was about 25% He and 75% H and little heavier elements. heavier elements.

• First generation stars had no heavy elements for First generation stars had no heavy elements for rocky planets or life.rocky planets or life.

• First generation stars make elements in core.First generation stars make elements in core.• New elements released into interstellar medium New elements released into interstellar medium

when star dies either as planetary nebula or when star dies either as planetary nebula or supernova. supernova.

Life of a StarLife of a Star

• Birth: collapse of gas cloud forms protostar.Birth: collapse of gas cloud forms protostar.• Main sequenceMain sequence: center of star becomes hot : center of star becomes hot

enough to burn Hydrogen into Helium. Our enough to burn Hydrogen into Helium. Our Sun will be on main sequence for 10 billion Sun will be on main sequence for 10 billion years.years.

• Red GiantRed Giant: Outer part of star expands and : Outer part of star expands and cools. Core contracts and starts to burn He cools. Core contracts and starts to burn He into Carbon and other heavier elements.into Carbon and other heavier elements.

• Star dies: either as a planetary nebula (low Star dies: either as a planetary nebula (low mass star) or as a mass star) or as a supernovasupernova (high mass star). (high mass star).

SupernovaeSupernovae

• Gigantic stellar explosions.Gigantic stellar explosions.• Eject new chemical elements into space.Eject new chemical elements into space.• Make neutron stars and black holes.Make neutron stars and black holes.• Accelerate cosmic rays (energetic particles Accelerate cosmic rays (energetic particles

constantly hitting Earth’s atmosphere from constantly hitting Earth’s atmosphere from space).space).

• Shock waves can help gas clouds to Shock waves can help gas clouds to collapse and form new stars.collapse and form new stars.

• Deadly to life (within say ~1-300 light Deadly to life (within say ~1-300 light years???)years???)

Origin of EarthOrigin of Earth

• Why are there planets? To conserve Why are there planets? To conserve angular angular momentummomentum (amount of spin). (amount of spin).

• (Linear) (Linear) momentummomentum is mass times velocity. is mass times velocity.• Angular momentum is momentum times distance Angular momentum is momentum times distance

from rotation axis.from rotation axis.• Think of an ice skater in a spin. With her arms Think of an ice skater in a spin. With her arms

apart she spins slowly (her hands have a small apart she spins slowly (her hands have a small momentum times a large distance from her momentum times a large distance from her rotation axis). As she brings her hands in she rotation axis). As she brings her hands in she spins much faster. Angular momentum is spins much faster. Angular momentum is conserved. Because her hands are nearer the conserved. Because her hands are nearer the rotation axis they must have a higher momentum rotation axis they must have a higher momentum and so she spins faster.and so she spins faster.

Collapse of Primitive Solar Collapse of Primitive Solar NebulaNebula

• Very extended gas cloud has, in Very extended gas cloud has, in general, a very small but nonzero general, a very small but nonzero rotation.rotation.

• As the cloud collapses the As the cloud collapses the conservation of angular momentum conservation of angular momentum causes it to rotate faster.causes it to rotate faster.

• Gas cloud can more easily collapse Gas cloud can more easily collapse along rotation axis so a round cloud along rotation axis so a round cloud flattens into a disk. flattens into a disk.

False color image of disk False color image of disk around Beta Pict.around Beta Pict.

Formation of Solar SystemFormation of Solar System

• The center of the disk collapses to form The center of the disk collapses to form a star.a star.

• While the rest of the disk forms a While the rest of the disk forms a system of planets.system of planets.

• Planets and star formed at same time.Planets and star formed at same time.

• All planets are expected to orbit around All planets are expected to orbit around the star in the same direction.the star in the same direction.

FormatioFormation of Star n of Star and and PlanetsPlanets

Planets versus Double StarsPlanets versus Double Stars

• Two ways to conserve angular Two ways to conserve angular momentum:momentum:– Form a single star with planets.Form a single star with planets.– Form two or more stars orbiting each Form two or more stars orbiting each

other (indeed many stars are observed other (indeed many stars are observed to be in binary or multiple star systems, to be in binary or multiple star systems, for example the nearest star Alpha Cent. for example the nearest star Alpha Cent. is a triple star system)is a triple star system)

• Expect planets to be common. Expect planets to be common.

Earth Formed HotEarth Formed Hot

• Large impacts continued.Large impacts continued.• Heat of formation melted rocks.Heat of formation melted rocks.• Dense Iron and other materials sank to Dense Iron and other materials sank to

form core of Earth leaving mantle depleted form core of Earth leaving mantle depleted in dense elements.in dense elements.

• Radioactive decay of Uranium, Thorium and Radioactive decay of Uranium, Thorium and Potassium helped to heat interior of earth.Potassium helped to heat interior of earth.

• Core cools by convection. Hot material Core cools by convection. Hot material rises and cold material sinks. This leads to rises and cold material sinks. This leads to rotating motions which carry heat away rotating motions which carry heat away from core.from core.

The Earth Cools by The Earth Cools by ConvectionConvection• Hot material near the core Hot material near the core

expands and becomes less expands and becomes less dense. It then rises. As it dense. It then rises. As it cools it becomes denser cools it becomes denser and sinks back to the core.and sinks back to the core.

• This rotary motion This rotary motion transports heat from the transports heat from the core.core.

• These motions can power These motions can power plate tectonics where plate tectonics where large plates move carrying large plates move carrying many surface features many surface features with them.with them.

• Convective currents also Convective currents also generate earth’s magnetic generate earth’s magnetic field.field.

CoreCore

Plate TectonicsPlate Tectonics

Formation Formation of New of New CrustCrust• As plates As plates

move apart, move apart, the Atlantic the Atlantic ocean is ocean is getting wider getting wider and new crust and new crust is forming in is forming in mid ocean.mid ocean.

• Age of crust:Age of crust:

Evolving Earth Crucial for Evolving Earth Crucial for LifeLife• Magnetic field shields cosmic rays Magnetic field shields cosmic rays

(radiation) from space.(radiation) from space.• Early atmosphere rich in COEarly atmosphere rich in CO22..• Greenhouse effect of COGreenhouse effect of CO22 very important for very important for

Earth temperature. Gases trap Sun’s heat Earth temperature. Gases trap Sun’s heat and keep it from being reradiated back into and keep it from being reradiated back into space. COspace. CO22 is transparent to visible light but is transparent to visible light but absorbs infrared radiation.absorbs infrared radiation.

• Without greenhouse effect, Earth would be Without greenhouse effect, Earth would be some 35 C colder (average temp. below -20 some 35 C colder (average temp. below -20 C instead of +12 C) and a frozen ice ball.C instead of +12 C) and a frozen ice ball.

Earth’s Thermostat Earth’s Thermostat

• Amount of COAmount of CO22 in atmosphere controlled by in atmosphere controlled by absorption to make carbonate rocks or out-absorption to make carbonate rocks or out-gassing from volcanoes.gassing from volcanoes.

• This changes greenhouse effect and Earth’s This changes greenhouse effect and Earth’s temperature.temperature.

• Earth’s temperature has been remarkably Earth’s temperature has been remarkably stable over its history despite an increase in stable over its history despite an increase in the Sun’s output.the Sun’s output.

• There must have been more COThere must have been more CO22 at early at early times and this somehow decreased in a way times and this somehow decreased in a way that compensated the increase in the Sun’s that compensated the increase in the Sun’s output.output.

We don’t understand this We don’t understand this ThermostatThermostat• We don’t understand many of the We don’t understand many of the

mechanisms which regulate COmechanisms which regulate CO22..• How much more COHow much more CO22 will lead to a will lead to a

runaway greenhouse effect such as what runaway greenhouse effect such as what happened to Venus?happened to Venus?

• What will the ultimate effect of human What will the ultimate effect of human produced COproduced CO22 be (global warming)? be (global warming)?

• How close did Earth come to losing COHow close did Earth come to losing CO22 and going into a permanent global ice age and going into a permanent global ice age (“snowball earth”)?(“snowball earth”)?

Venus is Hot as HellVenus is Hot as Hell

• Atmosphere is 90 Atmosphere is 90 times thicker then times thicker then Earth and mostly COEarth and mostly CO22..

• Greenhouse effect Greenhouse effect raises temp. by 400 C raises temp. by 400 C to about 470 C (hot to about 470 C (hot enough to melt lead).enough to melt lead).

• Not a likely place for Not a likely place for life. life.

Mars was once Warmer and Mars was once Warmer and Wetter Wetter • In the past, Mars In the past, Mars

atmosphere had much atmosphere had much more COmore CO22..

• This allowed This allowed greenhouse effect to greenhouse effect to raise temp. above 0 C.raise temp. above 0 C.

• Mars has since lost Mars has since lost most of its most of its atmosphere for atmosphere for unknown reasons, unknown reasons, perhaps absorption in perhaps absorption in rocks.rocks.

Formation of EarthFormation of Earth

• Planets and Stars from together from Planets and Stars from together from collapse of rotating gas cloud.collapse of rotating gas cloud.

• Sun and planets of same age.Sun and planets of same age.

• Planets all orbit Sun in same direction.Planets all orbit Sun in same direction.

• Earth formed hot. Rocks melted.Earth formed hot. Rocks melted.

• Denser material such as Iron sunk to Denser material such as Iron sunk to center and formed Earth’s Core.center and formed Earth’s Core.

• Radioactive decay continues to heat Radioactive decay continues to heat core.core.

Earth is Geologically Alive.Earth is Geologically Alive.

• We are lucky that Earth’s core is still hot and this We are lucky that Earth’s core is still hot and this heat flow drives convection, plate tectonics and heat flow drives convection, plate tectonics and generates magnetic field.generates magnetic field.

• Plate tectonics may help regulate CO2 in Plate tectonics may help regulate CO2 in atmosphere.atmosphere.

• Note, no other planet in solar system appears to have Note, no other planet in solar system appears to have plate tectonics.plate tectonics.

• Earth’s temp. remained remarkably stable despite Earth’s temp. remained remarkably stable despite warming Sun.warming Sun.

• Timeline: Big Bang 13 Bya, creation of chemical Timeline: Big Bang 13 Bya, creation of chemical elements 12-5 Bya, formation of Earth 4.6 Bya, elements 12-5 Bya, formation of Earth 4.6 Bya, formation of Moon in Big Whack 4.5 Bya, Large formation of Moon in Big Whack 4.5 Bya, Large impact basins on Moon 3.8 Bya, Origin of life 3.8 Bya.impact basins on Moon 3.8 Bya, Origin of life 3.8 Bya.

For next timeFor next time

• Read chap. 4 of Jakosky about the earliest Read chap. 4 of Jakosky about the earliest life and read “Vital Dust", pages 1-23 in life and read “Vital Dust", pages 1-23 in course packet about origin of life.course packet about origin of life.

• Think about your course project. Think about your course project. Read Read sample project “The Movie 2001 and the sample project “The Movie 2001 and the Evolution of Man”Evolution of Man”. Proposal (1-2 pages) . Proposal (1-2 pages) due Feb. 14, 2003.due Feb. 14, 2003.

• Next lecture, Friday. Feb 7, 2003, “Origin Next lecture, Friday. Feb 7, 2003, “Origin of Life”.of Life”.