Chapter 18 Life in the Universe

Continuous transformation of matter and energy that has led to the appearance of life on Earth - 7 phases

- Particulate - primal energy into elementary particles - Galactic - atoms into galaxies and stars - Stellar - stars into heavy elements - Planetary - elements into solid, rocky planets - Chemical - elements into building blocks of life - Biological - molecules into life itself - Cultural - advanced life forms into intelligence

Life & Culture Complexity

1) Living organisms can react to their environment and often can heal themselves when damaged 2) They can grow by taking in nourishment from their surroundings 3) They can reproduce, passing along some of their own characteristics to their offspring 4) They have the capacity for genetic change and can therefore evolve from generation to generation to adapt to a changing environment

If - life on Earth depends on just a few basic molecules - elements that make up these molecules are common to all stars - laws of science apply to the entire universe Then - Given sufficient time, life must have originated elsewhere in the cosmos Against: If -intelligent life on Earth is a product of extremely fortunate series of astronomical, geological, chemical, and biological events Then - life is unlikely to have occurred elsewhere in the universe

- Organic (carbon based) molecules - Building blocks of life - Amino Acids -> maintains life -- Build proteins which controls metabolism - Nucleotides -> masterminds life -- Form genes

- 1953 - Harold Urey and Stanley Miller - showed that building blocks of life form easily and spontaneously under early Earth conditions

- Mars - Jupiter's moon Europa

- Life forms that have adapted to live in extreme environments - Suggests life may be able to survive on harsh conditions of Mars, Europa or Titan

- Must ask HOW LIKELY life is to exist

Number of Intelligent Civilizations in the Galaxy N(comm) = R* x f(planets) x n(earthlike) x f(life) x f(int) x f(civ) x L(comm)

Rate of star Formation = 10/year Fraction of Stars w/Planetary Systems = 1 Number of Habitable Planets/Planetary System = 1/10 Fraction of Habitable Planets in Which Life Arises = 1 Fraction of Life-bearing planets on which intelligence arises = 1 Fraction of Life-bearing planets on which intelligence arises and uses technology = 1 **Average lifetime of a technological civilization = Unknown

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- Size of galaxy represents huge communication hurdle - distances of light years - Sending signal and receiving reply in our lifetime is not possible

- Earth has expanding 'bubble' of manmade radio signals expanding outward at speed of light - Receiving a reply i the lifetime of our civilization is not possible

- Search for Extraterrestrial Intelligence - Look for deliberate signals from et civilizations

- after decades of searching, scientists have found no trace of extraterrestrial intelligence - now, some of them hope to make contact by broadcasting messages to the stars

- Cosmic evolution is the continuous process that has led to the appearance of galaxies, stars, planets, and life on Earth - Living organisms are characterized by 4 traits - Amino acids and nucleotide bases are the building blocks of life - Life may have formed on Earth or been brought here by comets and meteors - Life in our solar system is most likely to be found on Mars and Europa - Life forms that have adapted to live in extreme environments are called extremophiles - Drake equation estimates the probability of other intelligent life in galaxy - Number of technologically advanced civilizations is approximately equal to the lifetime of typical civilization expressed in years - SETI listens for extraterrestrial broadcasts in electromagnetic spectrum