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The History of Life? Chapter 12 Where did life come from? • Many theories, ideas, and opinions exist • NO ONE knows exactly • Early idea: Spontaneous Generation – nonliving material can produce life • First disproved in 1668 by Francesco Redi (Italian Physician) – used decaying meat in jars to show that flies produce flies • See page 388 in textbook Experimental Group Control Group One jar was left uncovered. The second jar was covered. Maggots appeared on the meat in the open jar. Redi concluded that meat did not produce maggots. • Though Redi had disproved spontaneous generation of large organisms, many scientists thought that microorganisms were so numerous that they could arise spontaneously – from a “vital force” in the air • In mid-1800’s, Louis Pasteur designed an experiment that disproved the spontaneous generation of microorganims – see page 389 Figure 26.9 Pasteur and biogenesis of microorganisms (Layer 1) Figure 26.9 Pasteur and biogenesis of microorganisms (Layer 2) Figure 26.9 Pasteur and biogenesis of microorganisms (Layer 3) Biogenesis • “life comes from life” • Result of Pasteur’s experiment • Cornerstone of Biology Biogenesis does NOT answer origin of life… • Again, no one knows for sure, but there are several theories that have developed for HOW life on Earth originated 2 developments must have preceeded life on Earth: 1. simple organic molecules must have formed 2. These simple organic molecules organized into complex organic molecules – carbs, lipids, proteins, nucleic acids Alexander Oparin • 1930’s • Russian scientist • Hypothesized that life began in the oceans on the early Earth • Suggested that energy from sun, lightning, and Earth’s heat triggered chemical reactions that formed organic molecules • Rain washed these into the oceans – “primordial soup” • DID NOT DO ANY EXPERIMENTATION – purely theoretical Creating the potential for life Stanley Miller and Harold Urey • • • • • • • • • 1953 American scientists Tested Oparin’s hypothesis Simulated conditions of early Earth in lab Mixed water vapor with ammonia, methane, and hydrogen gases Sent in an electrical current (“lightning”) Cooled the mixture, collected liquids Found amino acids, sugars, and other small organic molecules See page 390 Figure 26.10 The Miller-Urey experiment Taking it further… • 1950’s – experiments showed that if amino acids are heated without oxygen present, they link and form proteins • Can also form ATP and nucleic acids in a similar manner • HOW FORMED FIRST CELLS? • Sidney Fox – American biochemist *demonstrated formation of protocells – large, ordered structures enclosed by membranes that carry out some life activities (growth and division) See page 391 in textbook *also called protobionts – not living, but show simple characteristics of life Endosymbiosis/ Gaia Theory • 1960’s • Proposed by American biologist, Lynn Margulis • Possible explanation for eukaryotic cell formation • Proof: separate DNA and extra membranes around mitochondria and Chloroplasts Endosymbiosis – Evolution from Bacteria Eukaryotic – chloroplasts inside… Eukaryotic – mitochondria inside… • endosymbiosis animation