Intelligent Life: Rare Event or Common Occurrence? A Dale Mabry Journal Club Presentation

Life - as we know it Life needs RNA AminoAcids Water (fluid) Life shows Cellular organization Inheritance/Reproduction Metabolism

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Even if bacterial life is relatively common, the main question is, do we share the Universe with intelligent life? “After all, Captain Kirk goes boldly where no humanoid went before NOT to search for new strains of bacteria or a moss”. (Shostak)

Shostak’s main argument is that intelligent life will evolve as the result of competition and natural selection among higher forms of life. Intelligent lifeforms Bacteria Metazoa

An attempt to calculate the likelihood of alien life in the galaxy Result? Hundreds or thousands of potential civilizations million

The endeavor (SETI) is a yes-or no-experiment. The search is a failure, until it suddenly becomes a success. (Shostak) VeryLargeArray Pioneer 10 Plague

Location!!!!

Critical Issues Position of star in the galaxy Lifetime and size of the star (habitable zones and timeframes) Planet with metals and large moon Large planets in the star system Several billion years without destruction Limited amount of global mass extinctions

N* = stars in the Milky Way galaxy --> 200 to 300 million fp = fraction of stars with planets --> 5-6% fpm = fraction of metal-rich planets --> less than 1% ne = planets in a stars habitable zone --> 1 ng = stars in a galactic habitable zone fi = fraction of habitable planets where life does arise fc = fraction of planets where complex metazoans arise fl = percentage of a lifetime of a planet that is marked by the presence of complex metazoans fm = fraction of planets with a large moon fj = fraction of solar systems with Jupiter sized planets fme = Fraction of planets with critically low number of mass extinction events Drake’s Equation Revisited

Summary There is mounting agreement and evidence supporting the potential for an abundance of bacterial life.

Summary “Intelligent” higher forms of life are either also abundant because they will inevitably evolve from bacterial life…

Summary …or higher forms of life are very rare (perhaps unique on earth) because the odds are heavily stacked against their appearance.