qualities of life - originated in early waters containing cyanide, methane, hydrocarbons, etc  

• movement - not necessary for life, nor possessed only by the living
• sensitivity - all living things respond to stimulus, but not all types of stimuli produce responses
• death - all living things die, but unless you can prove something is alive, then you can't kill it
• complexity - all living things are complex (but so are some nonliving things); can't define life by itself
• fundamental properties of life - cellular organization, sensitivity, growth (metabolism), development, reproduction, regulation, homeostasis

heredity - mechanism to improve the organism  

• genetic system w/ DNA allows for adaptation/evolution over time
• able to change and keep the new effects of the change
• viruses, microspheres aren't life because they can't reproduce/change by themselves
• evolution/heredity - essential to life; definition of life

hypotheses about the origin of life  

• special creation - oldest hypothesis; divine force placing life on earth
• panspermia (extraterrestrial origin) - meteors/cosmic dust brought organic molecules to earth; water on Europa, fossils on Mars indicate evidence of extraterrestrial life
• spontaneous origin - accepted by most scientists; life developed from inanimate objects as molecules became more complex
• earliest fossils date back 2.5 billion years
• special creation hypothesis isn't testable

earth's conditions when life appeared  

• very likely that 1st organisms lived at very high temperatures
• atmosphere - mostly CO2 and N2, w/ some water vapor, H2S, NH3, CH4
• reducing atmosphere - availability of hydrogen allows organic molecules to form more easily
• lack of oxygen allowed amino acids to last longer (normally would react w/ sugar and form CO2 in oxygen environment)
• atmosphere didn't change until organisms used photosynthesis to give off oxygen
• some claim that CO2 was locked up in the atmosphere, and lack of oxygen (and consequently ozone) would've allowed the UV rays to kill all early organisms

areas where life first originated - little agreement over where life first formed  

• ocean's edge - where bubbles form
• under frozen ocean - similar to ocean on Europa; unlikely that frozen oceans existed on hot, early earth
• deep in earth's crust - supported by Gunter Wachtershauser; volcanic activity recombined gases into life's building blocks; attempts to reproduce this effect used chemical concentrations far above those found during this time period
• within clay - surfaces have postive charges to attract organic molecules and exclude water (silicate surface chemistry)
• deep-sea vents - metal sulfides from vents attracted negatively charged biological molecules; supported by genomics (claim that early prokaryotes are closely related to the archaebacteria living on deep-sea vents)

Miller-Urey experiment - tried to reproduce conditions of early oceans in reducing atmosphere  

• started the new field of prebiotic chemistry
• placed an atmosphere rich in hydrogen and devoid of oxygen over liquid water at slightly below 100° C and used sparks to simulate lightning
• within a week, 15% of the carbon originally in methane formed simple carbon compounds (which later formed more complex molecules, including amino acids)
• over 30 different carbon compounds could be created

chemical evolution - disagreement over whether RNA originated before or after proteins  

• RNA supporters
  • RNA required for molecules to form consistently
  • ribozymes - RNA molecules acting as enzymes (replacing role of proteins)
• protein supporters
  • w/o enzymes, nothing could replicate
  • RNA nucleotides - too complex to form spontaneously
• Julius Rebek - created synthetic nucleotide-like molecules that can replicate and make "mistakes" (mutations)
• PNA (protein-nucleic acid)
  • came before RNA
  • basis for early life
  • simple enough to form spontaneously and self-replicate