Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Life Start with the Early Earth… • Hot ~ 230C • Oceans (at about 4.2 By) • CO2 atmosphere with ammonia, methane, water vapor, and nitrogen • Lots of UV-radiation (no ozone) • Reducing conditions • Lots of lightning Miller-Urey Experiment • Idea was that conditions on the primitive Earth could produce chemical reactions that made organic compounds from inorganic material. • Used water (H2O), methane (CH4), ammonia (NH3), and hydrogen (H2) • Made up to 22 different amino acids • After a week about 10– 15% of the carbon within the system was now in the form of organic compounds So we have organics…. • Turns out that there are lots of other possible origins for organics molecules – Deep sea vents – Spontaneous formation of peptides – Radioactive beaches – And many, many more… • Now you need to make cells…. • There are, of course, piles of theories on the origin of cells – – – – Clays Lipids Polyphosphates PAHs PAHs: Self Organizing Building Blocks? • Polycyclic Aromatic Hydrocarbons (PAHs) are amphiphilic (they have parts that are both hydrophilic and hydrophobic). • In solution, they tend to self organize themselves in stacks, with the hydrophobic parts protected. • In this self ordering stack, the separation between rings is 0.34 nm, the same separation found in RNA and DNA. • Smaller molecules will naturally attach themselves to the PAH rings. However it happened… • We think prokaryote cells (single-cell organisms that lack a nucleus) developed as early as ~ 3.85 Billion years ago • WE KNOW that by 3.5 Billion years ago we had bacteria and blue-green algae • By 2 Billion years ago we had eukaryotes (organism whose cells have a nucleus) • By 1 Billion years ago we had multicellular life • By 600 million years ago we had simple animals By 2.5 Billion years ago plankton were altering the oxygen content of the atmosphere What are the requirements for Life • Liquid Water – Too close….water boils off – Too far….water freezes • A source of Energy – Solar – Tidal • Available Organic Molecules – Carbon Compounds….abundant in comets and some asteroids • Enough Time – A stable environment – Evolve Complexity • This comes together in the concept of a Habitable Zone But there are a few other things… • • • • • • Stable Sun Near-circular planetary orbits Earth-like planetary mass Night and Day No major orbital disruptions Occasional mass extinctions are OK – But not too often…. Galactic Habitable Zones • It is all about stability • If it takes stability for over 4 billion years to develop intelligent life, you need to be in the Galactic suburbs • Stay away from – – – – Black holes High star density areas (comets) Star forming regions Supernova • For a start, stay away from the Galactic center Metallicity • No planets have been found around stars with less than 40% of the Sun’s metal ratio • Too high metallicity is also a problem (we think…..) – Tend to larger, more volatile-rich, lower-relief – Water-covered – Easier to form gas-giants…could be bad for terrestrial Planets • Metallicity increases steadily toward the Galactic center – More matter, faster star formation Co-rotation • Another thing to avoid is transiting spiral arms • These are areas of high stellar density and high star formation – Increases probability of close gravitational encounters – Or being to close to Supernova • Our Sun’s galactic orbital period is about the same as rotation period the nearby spiral arm The Drake Equation • R*Fp*Ne*Fl*Fi*Fc*L = N – R = The number of suitable stars, effectively F, G, and K stars, that form in our galaxy per year (about 1) – Fp= The fraction of these stars that have planets (about 0.5) – Ne = The number of Earth-like planets (planets with liquid water) within each planetary system (we are learning about this now…..expect an answer in 3-5 years) – Fl = The fraction of Earth-like planets where life develops (we could have some idea in 20 years) – Fi = The fraction of life sites where intelligent life develops (how are we ever going to know this?) – Fc = The fraction of intelligent life sites where communication develops (one would do….) – L = "The "lifetime" (in years) of a communicative civilization (how long have we been a communicative civilization?) – N = The number of communicative civilizations within the Milky Way today The Drake Equation • R*Fp*Ne*Fl*Fi*Fc*L = N • Drake thinks that N is about 10,000 for our Galaxy. • I really doubt that….. – Throw into the equation the limitations of metallicity, local star density, near-by supernova, and binary systems • But a few would not be unreasonable How can we tell if there is life? • Look at the atmosphere…. • Life uses the atmosphere as a source of energy and a sink for waste products. • We should know about nearby systems in ~20 years But we haven’t we found any communicative civilizations • Well….….there may be nothing to find. • Think about it…..how would an advanced civilization communicate? – How long has it been since Marconi invented radio? – Transatlantic commercial service was established in 1907 Big Questions… • Is there life elsewhere in our solar system? – There is no evidence • Is there intelligent life elsewhere in the Universe? – There is no evidence