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The Origin of Life on Earth Abiogenesis

The Origin of Life on Earth Abiogenesis. How Can We Study a Unique Event that Happened Several Billion Years Ago? Necessary Conditions for the Origin of Life Protobionts: Enclosing Prebiotic Systems Photosynthesis Is the Source of Atmospheric O 2 Is Life Evolving from Nonlife Today?

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The Origin of Life on Earth Abiogenesis

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  1. The Origin of Life on EarthAbiogenesis How Can We Study a Unique Event that Happened Several Billion Years Ago? Necessary Conditions for the Origin of Life Protobionts: Enclosing Prebiotic Systems Photosynthesis Is the Source of Atmospheric O2 Is Life Evolving from Nonlife Today? Does Life Exist Elsewhere in the Universe?

  2. How Can We Study a Unique Event that Happened Several Billion Years Ago? • Universe - 13 billion years ago • Earth - 4.5 b.y.a. • Life - ~ 3.5 b.y.a.

  3. How Can We Study a Unique Event that Happened Several Billion Years Ago? • Hypothesis: Life arose by chemical evolution • Pre-life processes observed in biochemistry

  4. Necessary Conditions for the Origin of Life • Earth at the time of life’s origin: • reducing atmosphere and energy (uv and lighting (and from earth). • result: small molecules (monomers) essential to living systems form and polymerize.

  5. figure 25-02.jpg Figure 25.2

  6. Proposed Life-Generating Environments • Reducing Atmosphere + Lightning (methane hydrogen, ammonia, water) Urey and Miller experiment. • Hydrothermal Vents (hydrogen sulfide + carbon dioxide + heat in the deep ocean) • Deep/Hot theory (deep inside the crust) • Primitive Clays Crystal structures in clays which could spontaneously catalyze the formation of certain prebiotic polymers. • Oily Bubble theory • Exobiology Life came here from elsewhere

  7. Proposed stages of abiogenesis • Stage 1: The origin of biological monomers • Stage 2: The origin of biological polymers • Stage 3: The chemical evolution from molecules to a cell with a high level of information.

  8. Necessary Conditions for the Origin of Life • Polymerization reactions: • generate proteins and nucleic acids • molecules accumulated and concentrated • Chemical evolution?

  9. Protobionts: Enclosing Prebiotic Systems • Protobionts- aggregation of polymers...living cell precursors • The earliest protobionts probably had lipid-based membranes.

  10. figure 25-03.jpg Figure 25.3

  11. Protobionts: Enclosing Prebiotic Systems • First genetic material (information storage) – (RNA rather than DNA?) • RNA had both enzyme function and an information transfer function. • Some RNA’s—called ribozymes—have catalytic (enzymatic) functions today. • \

  12. figure 25-04.jpg Figure 25.4 RNA - can fold up and function as enzyme Figure 25.4

  13. Protobionts: Enclosing Prebiotic Systems • DNA might possibly have evolved after RNA-based life became surrounded by membranes that provided an environment in which DNA was stable.

  14. Photosynthesis Is the Source of Atmospheric O2 • Cyanobacteria, first evolved photosynthesis...the ability to split water into hydrogen ions and O2, creating atmospheric O2. • O2 in the atmosphere made possible the evolution of aerobic metabolism • Ozone layer develops

  15. Living Bacterial mats Fossilized bacterial mats

  16. Stromatolites

  17. some of the oldest fossils- 3.5 billion years!

  18. Is Life Evolving from Nonlife Today? • Experiments by Louis Pasteur and others convinced scientists that life does not come from nonlife on Earth today. • Bacteria already in existence would eat any sort of prebiotic “soup.”

  19. figure 25-06.jpg Figure 25.6 Figure 25.6

  20. Is Life Evolving from Nonlife Today? • New life is no longer being assembled from nonliving matter - why? • molecules are oxidized • molecules are consumed

  21. Does Life Exist Elsewhere in the Universe? • Conditions that permit the evolution of single-celled prokaryotic life may be widespread in the universe!!!

  22. Does Life Exist Elsewhere in the Universe? • But, multicellular life is probably rare.... more stringent requirements. • planet with a relatively circular orbit • a rapid rate of spin • nearby planets that intercept impacts • large moon that stabilizes the planet’s orbit

  23. Does Life Exist Elsewhere in the Universe? • Although conditions on Earth have fluctuated greatly, they have been suitable for multicellular organisms for nearly a billion years. • i.e., 1,000,000,000 years...

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