1Is there extra-terrestrial Life?Is there Intelligent extra-terrestrialLife?2Life on Earth• Life formed on Earth relativelysoon after the planet’sformation 4.5 billion years ago• For 75% of the Earth’s history,only algae and single-celledlife forms existed• By 250 million years (5%)before the present, dinosaursand early mammals hadevolved.• Hominids, our distantancestors, developed 5.5million years ago (0.1%)• Homo Sapiens evolved only500,000 years ago! (0.01%)Living organisms like those on the Earth may exist on planets going around stars other than the Sun because a) we have detected comets in other stellar systems. b) life here may have been 'planted' by other civilizations. c) lifeforms on Earth may have disseminated elsewhere. d) the laws of physics and chemistry are universal. e) some stars emit radio signals.3• Life tends to draw on the substances thatare most plentiful: Carbon, Nitrogen,Oxygen and Hydrogen• Amino acids are organic moleculescontaining these substances• Amino acids form proteins, whichprovide structure and energy to cells• All life contains DNA – this instructionpacket contains all the informationneeded to build an organismThe Search for Life on Mars• It appears that Mars atsome point in itshistory was very muchwetter and warmerthan it is today• Scientists have beenlooking for life there• The Viking landers(1970’s) tested for thepresence of microbes,but returnedinconclusive results• We are still looking!4Life as we know it on Earth could only form in a "habitablezone", which is the range a) in the galaxy where there is enough oxygen. b) of distances from a star where most water will be liquid. c) of latitudes that stay warm during an ice age. d) of time when there is no longer bombardment by cometsand asteroids.Fossils of Ancient Martian Life?5S.E.T.I.How would we estimate the chances of Intelligent life being found elsewhere in the universe?How would we search for them?SETI• SETI: Search for Extra-TerrestrialIntelligence• Listens for electromagnetic evidence ofintelligence elsewhere in the universe• To date, evidence has been sparse.6Drake Equation! N = N*• fp• Ne• fl• fi• fc•L /TgEstimates the number of observable civilizations in the Galaxy• N is the number of civilizations in our galaxy with which we might hope tobe able to communicate;• N∗ is the number of stars in our Galaxy• fp is the fraction of those stars that have planets• ne is the average number of planets that can potentially support life per starthat has planets• fℓ is the fraction of the above that actually go on to develop life at somepoint• fi is the fraction of the above that actually go on to develop intelligent life• fc is the fraction of civilizations that develop a technology that releasesdetectable signs of their existence into space• L is the length of time such civilizations release detectable signals intospace.• Tg is the age of the galaxy.Drake Equation! N = N*• fp• Ne• fl• fi• fc•L /TgEstimates the number of observable civilizations in the Galaxy Historically: R* = 10/year (10 stars formed per year, on the average over thelife of the galaxy) fp = 0.5 (half of all stars formed will have planets) ne = 2 (2 planets per star will be able to develop life) fl = 1 (100% of the planets will develop life) fi = 0.01 (1% of which will be intelligent life) fc = 0.01 (1% of which will be able to communicate) L = 10,000 years (which will last 10,000 years)Drake's values give N = 10 × 0.5 × 2 × 1 × 0.01 × 0.01 × 10,000= 10.7• Current Best estimates:•fp = the fraction of those stars which have planets•Estimated by Drake as 0.5. It is now known from modern planet searches that at least10% of sunlike stars have planets, and the true proportion may be much higher, sinceonly planets gas-giant size and larger can be detected with current technology.[3]•ne = Estimated by Drake as 2. The same paper by Marcy, notes that most of theobserved planets have very eccentric orbits, or orbit very close to the sun where thetemperature is too high for earth-like life.•fl = In 2002, Charles H. Lineweaver and Tamara M. Davis estimated fl as > 0.13 onplanets that have existed for at least one billion years using a statistical argumentbased on the length of time life took to evolve on Earth.•fi = Some estimate that solar systems in galactic orbits with radiation exposure aslow as Earth's solar system may be more than 100,000 times rarer, however, giving avalue of fi = 1×10-7.•fc = 0.01•L = 10,000 for L is still the most popular estimate•R* = 6/year, fp = 0.5, ne = 2, fl = 0.33, fi = 0.01, fc = 0.01, and L = 10000 years•N = 6 × 0.5 × 2 × 0.33 × 0.01 × 0.01 × 10000 =