Are we alone? Life elsewhere in the universe?

Are we alone???? Rate the following statements from 1 (absolutely not) to 10 (definitely) and be ready to explain why you think that way 1. Other than the solar system, there are other planets in the milky way and/or universe. 2. There are rocky earth-like planets in the milky way and/or universe. 3. There are earth-like planets with liquid water in the milky way and/or universe. 4. There is single-celled life somewhere else in the solar system. 5. There is single-celled life somewhere else in the universe. 6. There is multi-cellular life somewhere else in the universe. 7. There is intelligent life somewhere else in the universe. Which of these has been scientifically confirmed? Which of these do you think will be confirmed in your lifetime? (Keep in mind, science looks for evidence…it’s not a poll like this.)

What does life have in common? (a.k.a.—How much biology do you remember?) Cells Responsiveness to stimuli Growth Reproduction Energy transformation Life forms on Earth are carbon-based Life forms on Earth require water (but water itself is not carbon based…H 2 O)

Some Requirements of Life Liquid water (for chemical reactions and as transport medium). Atmosphere (to avoid rapid vaporization of water; gasses needed for organic compounds) Moderate temperatures (keep water liquid; avoid disintegration of organic compounds; activate complex chemical reactions) Time for life to evolve from simple organic compounds into higher life forms: several billion years.

Simple to complex Life on Earth is varied, but all coded in DNA. Chains of billions of atoms did not drift together spontaneously, organized, and related. Miller-Urey Experiment (1952) : glass container was sealed with water (like the oceans), hydrogen, methane, and ammonia (similar to the gases present on a volcanic, young Earth), and an electric spark (like lightning from a thunderstorm). Life was not produced, but the building blocks, were. Organic molecules were made from inorganic compounds by physical means.

How did life begin? Life began as single celled prokaryotes (no nucleus) like bacteria. We have fossil evidence of cyanobacteria and stromatolites that date to 3.5 billion years. Prokaryotes engulf other prokaryotes to create eukaryotes (with a nucleus). Earth’s early atmosphere changes over to contain more oxygen due to photosynthesis of these early organisms. More complex eukaryotic cells evolve over billions of years. Modern stromatolites

What do we look for in stars? Habitable zones have…. Stable orbit around the star  consider only single stars. Time for evolution  consider only class F5 or less massive stars. Moderate temperatures  Habitable zone around the star

Life in Our Solar System? Most promising candidate: Mars. Mars rovers Spirit and Opportunity found evidence for past water on Mars.

Life in Our Solar System? Europa (moon of Jupiter) or Enceledus (moon of Saturn) Why are we curious about these moons? Cracks and smoothness of the surface might indicate liquid water beneath the surface. Tidal flexing could be the source of heat the keeps water in liquid form under the surface.

Signatures of life? What do we look for on an exoplanet? We look at the spectral lines reflecting off the planets’ atmospheres Water Oxygen Carbon dioxide Ozone (and reduced gases like nitrous oxide or methane) Ozone water Carbon dioxide

What have we found so far? Evidence of water on Mars in the past Glycine, an amino acid, found in comet ~700 planets outside our solar system (and counting) Planet inside Habitable zone around a star like our Sun …..but no life …..yet.