What is Life? • “Life is what dies when you stomp on it” -Dave Barry • Simple definitions all fail • Moves? Grows? Feeds? Reproduces? • Best definitions focus on: • Self-organizing, complexity, adaptation • Information coding • Feedback (homeostasis)
DNA • Deoxyribonucleic acid • Total length of human DNA in a single cell is about a meter • A human body contains about 20 trillion cells • The total length of DNA in a human body is thus 20 trillion meters, or twenty billion kilometers, the circumference of the orbit of Pluto.
Prebiotic Evolution • The basic molecules of organic chemistry are easily made • The first self-replicating molecule was almost certainly not DNA • DNA assembles from simpler materials all the time • Many likely candidates • Clay minerals as templates?
Plants and Animals • CO2 + H2O + Energy = Sugars, Starches, etc. + O2 (toxic waste) • 12CO2 + 11H2O --> C12H22O11(Sucrose) + 12O2 • O2 is actually toxic (even to us!) • Idea: Take the sugars and starches (from somebody else) combine it with the waste O2, and get the energy back
Planetary Habitable Zones • Primarily in the Liquid Water Zone • Can’t be too warm • Water Vapor in upper atmosphere broken down by solar UV and charged particles (photodissociation) • Hydrogen escapes to space • Too hot planets will quickly lose all their water • Freezing not so much of a problem
Reasons to be a "Carbon Chauvinist". • Carbon is abundant in the Universe • Carbon can bond to four neighboring atoms • Carbon can bond to other carbon atoms, sharing one, two, or three electrons • These properties make it possible to form a vast array of organic molecules • No other element has these properties
Reasons to be a ”Water Chauvinist". • Water stays liquid over a wide range of temperatures. • Water is very abundant in the Universe • Water is a polar or asymmetrical molecule. It attracts ions easily, making it a good transporter of nutrients • It does not dissolve organic molecules (so we do not dissolve in our own cell fluids)
Alternate Biologies? • Ingredients need to be abundant in Universe • Need solids to maintain structure • Need liquids or gases to transport nutrients and wastes • Need source of energy • High temperatures destroy complex molecules • Also solid state electronics • Why your computer has a fan
Alternate Biologies? • Silicon? Earth’s crust is 27% Si • If silicon biology is possible, why not here? • Silicon doesn’t bond to itself well • C + O = gas, Si + O = quartz • CO2 dissolves in water, SiO2 doesn’t • (SiH4 and SiF4 are gases, however) • Alternatives to water? • Ammonia? Polar like water • Methane? Not polar • Hydrogen peroxide?
Alternate Biologies? • Nitrogen or Phosphorus? • Can form complex molecules • Both rarer in universe than carbon • Arsenic? • Alternative to phosphorus • Even rarer in Universe • Chlorine • Alternative to oxygen? • Rarer in Universe than oxygen
Alternate Biologies? • Sulfur? • Not likely as alternative to carbon • Can be alternative to oxygen – even on earth • We cannot design a probe to look for “alternative biology” because we just don’t know what to look for.
Earth’s Alternative Biologies • Extremophiles: organisms that thrive under extreme temperature, pressure, or chemical conditions • Many of Earth’s simplest organisms are extremophiles • Extremophile domain is a bigger target • We’re more likely to find planets inhabitable by extremophiles than planets suitable for humans
Arsenic-Eating GFAJ-1 • Not “arsenic based” life • Organic structures built of carbon • More than merely able to utilize arsenic • Can apparently replace P with As • Up till now, P considered absolutely essential • Seems to build As into DNA instead of P • What about Si?
Life on Early Earth • Oldest minerals: 4.4 b.y. • Oldest rocks: 4.2 b.y. • Probably no life until Late Heavy Bombardment over (3.8 b.y.) • Large impacts would sterilize Earth • Liquid water as far back as we can see • Life by 3 b.y.
Life on Early Earth • Faint Early Sun • Sun 4 b.y. ago was 70% as bright as today • We have liquid water throughout Earth history • Probably thick greenhouse atmosphere • How life originated? • Cold earth: improves chemical stability • Hot Earth: speeds up chemical reactions • Use minerals as templates?
You can buy the exact number and proportion of atoms to make a human for only a few dollars. • You can buy the exact number and proportion of atoms to make a Lexus from a junkyard for only a few dollars, too • If you want to talk about the exact arrangement of the atoms, the price goes up sharply. • Buying the exact organic molecules that make up a human would cost millions of dollars, and many cannot yet be synthesized at all
The Ultimate Long-Term Forecast • Slow warming trend for the next billion years • Increasing humidity • CO2 decrease leads to extinction of plants? • Boiling and evaporation of the oceans
Surviving on a Warming Earth • Higher organisms stop reproducing around 50C • There will be no place cool to hide • Possible evolutionary strategies • Ultra sturdy heat resistant molecules • Concentrated solutions to raise boiling point • Retreat underground where pressure and boiling point higher • Pressurized cells • Ultimate limit 150-200 C?
Surviving on a Warming Earth • Plants need > 10 ppm CO2 • Animals and plants die around 50 C • Micro-organisms can tolerate 130 C + • But biology seems to like heat and we have a billion years to experiment • Pressurized cells? • Anti-boiling fluids? • Problem is breakdown of organic molecules • 150 - 200 C (300-380 F) max?
The Oreo Model of Life History Micro-organism Earth (0-3 billion years) Multicellular Earth (3-5 billion years) Micro-organism Earth (5-6 billion years) “The white creamy middle”
The Drake Equation • “A wonderful way to organize our ignorance” • - Jill Tarter
The Drake Equation • Number of Intelligent Civilizations = • Number of Stars in the Galaxy (400 billion) • x Fraction of Stars with Planets (1/4?) • x Number of suitable planets per star (0.1?) • x Fraction of planets where life appears (1/2??) • x Fraction of planets with intelligence (???) • x Fraction of planets with technology (????) • x Fraction of planet’s life with technology (??????)
So Where Are They? • Populations expand exponentially • It would take an exponentially-growing civilization only a few million years to fill the Galaxy, even at sub-light speeds • 2 to the 40th power is over a trillion • If it takes 10,000 years for a colony to achieve interstellar travel, 40 doubling times is only 400,000 years. • So why aren’t they all around us?
Is There A Problem? • Alien psychology? We barely understand humans! • Why did it take us so long to develop technology? • Maybe we’re first? • Maybe we’re unique?
Other Stuff For the Drake Equation • Jupiter Stabilizes Solar System? • Jupiter lessens impact bombardment • Moon stabilizes Earth’s axial tilt • Earth’s magnetic field deflects cosmic rays • Liquid Water Zone is narrow and changes with time as stars brighten • Center of the Galaxy Deadly?
What if we succeed?Some Features of Culture Shock • Loss of Faith in Beliefs and Institutions • Xenophobia • Over-Dependence, Copying • Nihilism
Models for Alien Encounters • Star Trek? • We’re OK, they’re OK (Klingons sort of, Romulans not so much) • War of the Worlds? (Also the Borg) • We’re food (or in the way) • Watership Down? • We’re irrelevant
Why Would Aliens Want Earth? • If they can freely travel in space: • Water from icy bodies and comets • Hydrocarbons and organic molecules from gas giants and frozen methane • Oxygen from silicates and water • Metals from asteroids • Unlimited size solar collectors close to Sun for Energy • We are not likely to be • A threat • A source of anything useful
Why Would Aliens Want Earth? • A Planet to Live On • Convenient working conditions • Lithophile Elements • Hydrothermal ores • Organic materials • It probably won’t be about us • Not that it will make it any easier
“Wonderful, just wonderful. So much for instilling them with a sense of awe.”
“Matthews, we’re getting another one of those strange ‘aw-blah-es-pan-yol’ sounds.”
Arthur C. Clarke’s Laws • The only way to test the limits of the possible is by going beyond them into the impossible • When an elderly but distinguished scientist says something is possible, he is probably right. When he says something is impossible, he is very likely wrong • Any sufficiently advanced technology is indistinguishable from magic
No Point in Hiding • At Radio Frequencies, Earth is brighter than the Sun • Our Radio signals are now 70+ light years out • From our signals, aliens could determine: • Length of our day and year • Size of Earth, Distance from Sun • Probable mass and gravity • Draw a crude map of Developed World
Our Views of Aliens • Post World-War II • “Savior Model” • “Hostile Aliens” - Eat or Enslave • Science Source of Fascination and Fear • Winning World War II • Nuclear War • Similarity with Westerns • We’re the Good Guys • Fighting off Hostile Threats
Our Views of Aliens Evolve • 1960’s: “Hostile Alien” films and Westerns both decline • We’re Not Always the Good Guys • Historical Revision of Frontier • “Spaghetti Westerns”-Dark and satirical • Civil Rights Movement • Vietnam • Star Trek, 1967 • Enlightened, Optimistic Future
Variations • Humans as Helpers: E.T. • Encounter as Wonder: Close Encounters of the Third Kind • Encounter as Dreary: Contact • Swashbuckling: Star Wars • Satire: Men In Black • Return to Hostile Aliens • Star Trek Spinoffs(The Borg, the Dominion) • Independence Day