1. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Origin of Life In 1862, Louis Pasteur conducted experiments that rejected the idea of spontaneous generation.

2. All life today arises only by the reproduction of preexisting life, the principle of biogenesis. Conditions on the early Earth were very different. little atmospheric oxygen Energy sources, such as lightning, volcanic activity, and ultraviolet sunlight Sometime between about 4.0 billion years ago, when the Earth’s crust began to solidify, and 3.5 billion years ago the first organisms came into being. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

3. Hypothesis- chemical and physical processes in Earth’s primordial environment eventually produced simple cells. (1) the abiotic synthesis of small organic molecules; (2) joining these small molecules into polymers: (3) origin of self-replicating molecules; (4) packaging of these molecules into “protobionts.” Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

4. In the 1920’s, A.I. Oparin and J.B.S. Haldane independently postulated that conditions on the early Earth favored the synthesis of organic compounds from inorganic precursors. They reasoned that this cannot happen today because high levels of oxygen in the atmosphere attack chemical bonds. Abiotic synthesis of organic molecules is a testable hypothesis Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

5. The reducing environment in the early atmosphere would have promoted the joining of simple molecules to form more complex ones. The considerable energy required to make organic molecules could be provided by lightning and the intense UV radiation that penetrated the primitive atmosphere. Young suns emit more UV radiation and the lack of an ozone layer in the early atmosphere would have allowed this radiation to reach the Earth. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

6. Oparin-Haldane hypothesis - conditions on the early Earth favored the synthesis of organic compounds from inorganic precursors In 1953, Stanley Miller and Harold Urey tested this hypothesis by creating, in the laboratory, the conditions that had been postulated for early Earth. They discharged sparks in an “atmosphere” of gases and water vapor. H 2 O, H 2, CH 4, and NH 3 The experiments produced a variety of amino acids and other organic molecules. Alternate sites volcanoes & deep-sea vents meteorites

7. The abiotic origin hypothesis predicts that monomers should link to form polymers without enzymes and other cellular equipment. Polymers (polypeptides)form from monomers on hot sand, clay, or rock. Laboratory simulations of early-Earth conditions have produced organic polymers Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

8. Cells store their genetic information as DNA, transcribe genes into RNA, and translate the RNA messages into enzymes and other proteins. Many researchers have proposed that the first hereditary material was RNA, not DNA. RNA can also function as an enzymes, it helps resolve the paradox of which came first, genes or enzymes. RNA catalysts, Ribozymes catalyze the synthesis of new RNA polymers. RNA may have been the first genetic material Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

9. Short polymers of ribonucleotides can be synthesized abiotically in the laboratory. Ribozymes also help catalyze the synthesis of new RNA polymers. zinc can act as a catalyst - the copied sequences may reach 40 nucleotides with less than 1% error. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin CummingsFig. 26.11

10. In the pre-biotic world, RNA molecules may have been fully capable of ribozyme-catalyzed replication. RNA-directed protein synthesis - binding of specific amino acids to bases along RNA molecules -This is one function of rRNA in ribosomes. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

11. Living cells may have been preceded by aggregates of abiotically produced molecules which maintain an internal chemical environment from their surroundings and may show some properties associated with life, metabolism, and excitability. self-assembly of abiotically produced molecules Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

12. Liposomes behave dynamically, growing by engulfing smaller liposomes or “giving birth” to smaller liposomes. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 26.12a liposomes form a molecular bilayer, much like the lipid bilayer of a membrane

13. If enzymes are included among the ingredients, they are incorporated into the droplets. Some molecules produced abiotically have weak catalytic capacities. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 26.12b

14. Evolution - replacement of RNA as the genetic information by DNA, a more stable molecule. Laboratory simulations cannot prove but describe steps that could have happened to create life on the primitive Earth. organic monomers synthesized on early Earth or from comets and meteorites? Location - deep-sea vents? Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings

15. Oldest multicellular fossil Oldest fossil prokaryotic cell

16. The oldest fossils that have been uncovered were embedded in rocks from western Australia that are 3.5 billion years ago. The presence of these fossils, resembling bacteria, would imply that life originated much earlier. This may have been as early as 3.9 billion years ago, when Earth began to cool to a temperature at which liquid water could exist. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 26.3a

17. A great range of eukaryotic unicellular forms evolved into the diversity of present-day “protists.” Multicellular organisms, differentiating from a single-celled precursor, appear 1.2 billion years ago as fossils, or perhaps as early as 1.5 billion years ago from molecular clock estimates. Multicellular eukaryotes evolved by 1.2 billion years ago Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Fig. 26.6