CH18 - Astronomy 1F03 2010/11 Fall Term 2010/11 Chaisson...

Info iconThis preview shows page 1. Sign up to view the full content.

View Full Document Right Arrow Icon
This is the end of the preview. Sign up to access the rest of the document.

Unformatted text preview: Astronomy 1F03 2010/11 Fall Term 2010/11 Chaisson & McMillan, Astronomy Chapter 18 Life in the Universe Cosmic Evolution Cosmic The Universe has only become hospitable to life recently… hospitable There have been several phases refining the conditions and composition of the universe towards Earth-llike ike of habitable conditions habitable Evolutionary Stages Stages Particles 2. Galaxies/Structure 3. Stars 4. Planets 1. Chemistry 6. Biology 7. Culture 5. A complex chain of Events: complex Astronomy to Geophysics 1. 2. 3. 4. Particles Big Bang, Matter, Particles Hydrogen Hydrogen Galaxies/Structure A place to make Galaxies/Structure several generations of Stars several Stars A place to make Elements Stars place Planets A place to do complex Planets chemistry chemistry 5. 6. 7. Chemistry Biology Culture A complex chain of Events: complex Geophysics to Life Particles Particles 2. Galaxies/Structure 2. 3. Stars 4. Planets 1. Chemistry Complex molecules Chemistry Complex 6. Biology Complex life Biology Complex 7. Culture Astronomy ☺ Culture 5. Making Life… Making How did life arise? How Are organic molecules hard to make? Are e.g. Amino acids The Early Earth The The Early Earth was rich in Carbon Dioxide, Methane, Ammonia, Water, etc… etc Almost no Oxygen Almost Lots of radiation, Ultraviolet, storms (lightning) (lightning) Can you make more complex molecules? molecules? Miller-Urey Experiment Miller Urey & Miller 1953 Urey Start with simple chemicals like the Earth’s early Earth early atmosphere atmosphere Zap them for a week week Make amino-acids Make Steps to life… Steps Amino acids are the building blocks of proteins proteins Proteins (as enzymes) facilitate the key processes of life processes Amino acids are a key component of DNA DNA Chemical Evolution Chemical Follow-ups to the Miller-Urey Follow Urey experiment have made cell-like bags experiment A long way to go to life long BUT Cells on Earth took up to 1 billion years to appear to Life on Earth Life Indirect evidence: Stromatolites: 2-3 billion years ago Stromatolites Rusted iron deposits: Oxygen over 3 billion years ago billion Direct evidence: Cell fossils: Cell Over 2 billion years ago Amino acids from Amino Outer space… Amino acids have also been seen in space Amino in molecular clouds in in meteorites in Murchison Meteorite: (Australia 1969) Rich in organic material Rich including Amino acids including Steps to Life Steps Steps that could plausibly have made simple life forms have been reproduced simple We will probably never know the details of the first simple life of Evolution tends to weed out simple, inefficient versions … (e.g. RNA based organisms, inefficient (e.g. photosynthesis) photosynthesis) Complex Life Complex 1 Billion years ago multi-celled Billion celled organisms appeared organisms These ultimately led to plants, insects, animals and humans animals The driving process is evolution The Evolution is the theory associated with Charles Darwin Charles Case Study: Case Horse Evolution Evolution is not linear Evolution Species can appear at the same time and most disappear again disappear Fossils are rare and links hard to find for many species species Size is the easiest thing to change (elephant, elephant shrew) elephant Aside: Evolution vs. Creationism “Intelligent Design” Evolution is not a belief, it is a compelling theory that fits the scientific evidence evidence Creationism is not scientific – iit is t motivated by religious beliefs motivated “Intelligent design” allows minor allows evolution but claims things like human eyes are too complex to evolve eyes Aside: Intelligent Design Flawed Argument: Flawed Evolution is gradual Evolution Gradual means one piece at a time Gradual Eyes “don’t work” with missing pieces with (e.g. with no lens) (e.g. Therefore eyes could not have evolved Therefore Evolution of the Eye Evolution Eyes do work (or are at least useful) in simpler forms forms There are simpler versions of eyes found in living organisms: living Worms Flat worms Nautilus Fish + all Worms vertebrates vertebrates Useful things like eyes have evolved repeatedly in many different forms in Real eyes have flaws that are probably associated with how they evolved associated Life, but not as we know it… but Life on Earth is based heavily on Life Carbon chain molecules Carbon Water to dissolve things in Water Are there alternatives? Silicon (Think ALIEN the movie) Silicon Ammonia for a solvent? Ammonia Sulphur Sulphur Life as we know it Life Life probably requires large molecules, liquids/solvents and reliable energy sources sources On Earth the large molecules are carbon based and the solvent is water carbon What about Energy sources? What Energy for life Energy At the start of the food chain there are At organisms that get energy from a reliable non-living source, e.g. reliable Light Light Chemicals Chemicals Chemical Energy Chemical Bacteria can derive energy from many chemical sources including gases, heavy metals, some plastics and chemicals poisonous to humans poisonous You can only get energy from reactive chemicals not in their usual oxidized, low energy state energy Reactive chemicals must be generated, e.g. via geothermal activity (e.g. undersea volcanoes) volcanoes) Extremophiles: Life on the edge Extremophiles Deinococcus radiodurans can survive radiation doses 3000x higher than would kill humans Thermophiles can live 3 km under the continental crust A thriving ecosystem surrounding a deep sea hydrothermal vent (near 113oC): Life is more durable than we are Life Apollo 12 astronauts recovered Surveyor 3’s camera, contaminated with 50-100 strep camera, 100 bacteria, which survived launch, space vacuum, radiation exposure, an average temperature of only 20 degrees above absolute zero, and no nutrient, water, or energy source . . . For almost 3 years! energy Life outside Earth Life The Elements need to make a life are common in the universe common ii.e. Carbon, Hydrogen (Water), Oxygen, .e. Nitrogen, Sulphur, a few metals (e.g. Iron, Sulphur few Copper) and salts (e.g. Chlorides) Copper) Sunlight and geothermal energy are available The difficult part is probably a suitable environment – the liquid medium The Habitable Zone The The standard definition of a habitable zone is where liquid water can be found zone At pressures similar to Earth’s At atmosphere this requires temperatures in the range 0-100 Celsius in Habitable Zones Habitable Planets are similar to a blackbody: They radiate light as temperature T4 They Closer to a star the planet receives more light To reach a constant equilibrium temperature heat in equals heat out temperature The equilibrium temperature gets hotter closer to the star or if the star is brighter brighter Habitable Zones: Habitable Where liquid water can exist Habitable Zone in the Solar System Solar Three Potentially Habitable Planets? Habitable Venus, Earth and Mars are all in the habitable zone for the Sun the Earth has abundant liquid water and life… liquid Mars in the Habitable Zone Mars Liquid oceans, comparable atmospheric pressure to Earth for first 1 billion years pressure Surface gravity too low to hold atmosphere effectively for age of solar system Low pressure CO2 atmosphere now Low Martian Civilizations? Martian Lowell’s 1895 Canal Map Earth-based Observation 1991 Water on Mars? Water Dry River valleys, channels Dry “Splosh” craters Rounded rocks Rounded BUT: Last 3 Billion years: water locked up as permafrost locked Mars Rovers … “Guadalupe” Rover missions: Bedrock examination Chemicals: e.g. Iron/Magnesium Sulphate salts, Chloride/Bromide salts Sulphate salts, possible possible -> Long exposure to acidic water Long Appearance: Vugs? (holes due to Vugs (holes dissolving of salt), Crossbedding? Crossbedding Life on Mars? Life Viking probes tested for biological responses (perchlorate!) Biological fossil marks in Martian meteorite? Unlikely Martian Methane on Mars Methane has been very recently detected in Mars’ atmosphere detected Methane on Earth in made mostly by bacteria bacteria Methane would be destroyed on Mars in just a few hundred years just Is it Life? Active Volcanoes? Is Venus in the Habitable Zone Venus Very Earthlike: Similar composition, Very mass mass Quite likely liquid water never present: no dissolving of CO2, present: runaway greenhouse effect runaway Surface temperature 500 C Surface Acidic mostly CO2 atmosphere Acidic Alternative ways to use a Habitable Zone Habitable Locations for Earth-like life: Terrestrial Planets Terrestrial Migrated Ice Giants: Ocean Planets Migrated Moons around Gas Giants, comparable in mass to terrestrial planets, high ice content (Methane, Ammonia, Water, … ) Liquid Water by other means Liquid Tidal heating can maintain liquid water beyond the standard Habitable zone beyond The tidal heating could also create volcanoes to provide energy volcanoes Jupiter’s Moons Jupiter Europa Strong Magnetism, recent resurfacing indicate liquid interior interior Thick ice crust – several km Heated by tides/internal volcanism volcanism Indications of high acidity (PH 0) Indications Life on Europa? Europa Undersea vent type biochemistry usually invoked usually High sulphur content sulphur Very acidic? Very Ganymede and Callisto are other Ganymede Callisto are possibilities for a deep liquid water zone at one time at Probing Europa Europa Galileo probe burned up to avoid contamination contamination Need to drill or melt through several km of ice of Earth version: Lake Vostok, lliquid under Vostok iquid 3.7 km of ice (South Pole) 3.7 Saturn’s Moons: Titan Saturn Titan is a very large Moon (1.8 Earth Moons) Moons) Atmosphere: 10% Argon 90% Nitrogen Atmosphere: Complex photochemistry involving Methane, Nitrogen, Organic Compounds Methane, Huygens Probe Landing Huygens Methane/Ethane “seas” Water “rocks” Water Beyond Earth – lless habitable but ess habitable anyway? habitable The energy supply rate is very low but there are probably no Earth-llike “fast” ike there organisms to wipe out slow growers organisms either either In some cases (e.g. Mars), Earth-llike ike In life may have had time to adapt to increasingly harsh conditions increasingly Life in the Galaxy: Life Drake’s Equation Frank Drake (1963) first thought seriously Frank about searching for extra-terrestrial life about He tried to estimate how likely it was that He other civilizations exist in the Galaxy other Number of technological, intelligent civilizations now present in the Galaxy = Rate of star formation averaged over the lifetime of the the Galaxy x Galaxy Fraction of stars having planetary systems x systems Average number of habitable planets within those Average planetary systems x systems Fraction of those habitable planets on which llife arises x ife Fraction Fraction of those life-bearing planets on which Fraction intelligence evolves x evolves Fraction of those intelligent-life planets that develop Fraction technological society x Average lifetime of a technologically competent lifetime civilization Stars per year in the Galaxy? Stars Averaged over the lifetime Averaged 100 billion stars, 10 billion years 100 Around 10 stars per year Around Stars with Planet? Stars Planet searches have found a lot of large planets large Small planets are not detectable… yet Small It is optimistic but reasonable to assume all stars have planets assume Number of Habitable Planets? Number Many stars (about half) are binary binary Binary stars are unlikely to allow planets in the habitable zone zone In general terrestrial planets are not well constrained are Assume 1/10 of systems have a habitable planet habitable Fraction of Planets that develop life develop The ingredients and conditions for life are commonplace are Experiments indicate life-llike molecules ike Experiments are “easy” to generate Assume that life always develops on Habitable planets Habitable The likelihood of intelligent life? Technology? life? These are very uncertain These Is intelligence inevitable? Is Humans developed a technological civilization in a very short time compared to other stages of evolution compared Optimistically assume 100% likelihood for both for How long does a technological civilization survive? civilization In the 50’s and 60’s with the cold war In with people were pessimistic: 1000 years people Taking into account comet threats and so forth 1,000,000 years doesn’t seem so seem unreasonable unreasonable Overall odds? Overall It depends a lot on the assumed lifetime (the other factors multiply to 1) lifetime 1000 years 1000 civilizations right now now 1,000,000 years 1,000,000 civilizations in the Galaxy civilizations Nearest Civilization? Nearest 1,000,000 civilizations in the Galaxy implies nearest is around 30 pc away (100 light years) (100 Not a very convenient traveling distance… distance Voyager and Pioneer spacecraft have message plaques just in case… message Pioneer 10 Plaque Pioneer Radio Radio Signals Earth is brighter than the Sun in Radio Earth Signals modulate as continents pass over the horizon over SETI: Search for ExtraTerrestrial Intelligence ExtraTerrestrial Our best bet is signals – such as radio ~ 18-20 cm SETI has been searching for 50 years for SETI was originally funded through NASA through Once actively sent signals as well (Government didn’t as like that) like Arecibo Puerto Rico SETI: Search for ExtraTerrestrial Intelligence ExtraTerrestrial Allen Telescope Array Used by SETI & Used Berkeley Berkeley Collects data at cm Collects wavelengths wavelengths SETI has more data SETI than it can handle: SETI @ Home allows your PC to help your UFOs? UFOs? A few people currently believe (or claim) they few have met aliens have Several factors make this likely to be Several psychological or delusional in origin: psychological Difficulties of interstellar travel Difficulties Silly activities aliens supposedly do Silly Pop culture (e.g. movies) affect reports: reported aliens look like recent movie aliens reported ...
View Full Document

This note was uploaded on 04/10/2011 for the course ASTRONOMY 1f03 taught by Professor Wadsley during the Spring '11 term at McMaster University.

Ask a homework question - tutors are online