Origin of Life Beliefs • 1. Spontaneous Generation- idea that nonliving material can produce life ex. People believed decaying meat produced maggots ex. Mice suddenly appearing in sacks of grain • 1668- Francesco Redi (Italian physician) disproved spon. gen.
Disproving spontaneous generation • Redi disproving spon. Gen. allowed people to believe in biogenesis (idea that living organisms come from other living organisms) • SO HOW DID LIFE BEGIN ON EARTH?? • TO GET LIFE YOU NEED TO FORM ORGANIC MOLECULES (CONTAIN CARBON)
Early Earth Conditions • SO HOT!!! Due to radiation, volcanoes, friction from colliding meteorites • All eruptions of volcanoes made all gases present (CO2, N2, H2, CO, methane, and ammonia • H2O is present as water vapor b/c it’s so hot!!
Early Earth Conditions • About 3.6 byo (billion years ago) earth started to cool and H2O condensed to form liquid H2O *Rock evidence shows 1st life began then • Led to millions of years of rainstorms to form the oceans • Helps support Miller/Urey experiment
Formation of Organic Molecules • 1. Believed early atmosphere contained little free O2 • 2. Most atmosphere was made of (water vapor, carbon dioxide gas, nitrogen gas, methane gas, ammonia, hydrogen gas, and carbon monoxide • *1938 Alexander Oparin proposed Primordial Soup Theory (says life began in the oceans)
Primordial Soup Theory • Oparin said energy from sun, lightning, & Earth’s heat triggered chem rxns. to produce small organic molecules from substances present in Earth’s atmosphere • Then rain washed these molecules into oceans making this primordial soup • 1953 Stanley Miller/Harold Urey (American Scientists) wanted to test Oparin’s theory by simulating Earth’s early conditions in the lab
Miller/Urey Experiment • 1. Mix water vapor (steam) w/ ammonia, methane gas, and hydrogen gas • 2. Send electric current (simulates lighting) through it • 3. Cool gases- which produces a liquid that simulates rain • 4. Collect liquid in flask • 5. Results- found several kinds of amino acids, sugars, & other org. molecules that supported Oparin’s hypothesis
So, how do organic molecules lead to cells?? • Evolution of Cells • 1st cells- protocells- large structure w/ a membrane that contains the primordial soup & carries out cell division • Believed that prokaryotes evolved from protocells *Remember there is no free O2 present yet • So, 1st prokaryotes were heterotrophic anaerobes that ate primordial soup
Evolution of Cells • So, 1st autotrophic bacteria made food (glucose) by chemosynthesis by releasing energy of inorganic molecules & lived in harsh environments *Similar to present day archaebacteria that live in hot springs • 2nd autotrophic bacteria may have been photosynthesizing prokaryotes which released O2 in the atmosphere • Lightning striking the O2 would have formed O3 (ozone) and allowed more complex organisms (eukaryotes) to thrive
Endosymbiont Theory • *Believed that eukaryotes evolved from prokaryotes • 1960s- Lynn Margulis proposed this theory • She said eukaryotes evolved by symbiotic relationships w/ prokaryotes
Evidence to support Margulis’ beliefs • Cyanobacteria & chloroplasts (contain DNA & ribosomes) look similar & can both do photosynthesis • Some bacteria & mitochondria (contain DNA & ribosomes) look similar