Topics Early earth – environment and nutrient base – requirements for protobionts Hypotheses of origin of life Early prokaryotes Cell theory Eukaryote evolution Four major eras and their major events

Chemical Evolution - Life from Non-life Ch. 21 – Origin and Evolutionary History of Life, pp. 438-440. Chemical Evolution - Life from Non-life All organisms - same overall chemistry common, likely multiple origins Earth ~ 4.6 billion years old - Astrophysicists and Geologists Earliest fossils of life - 3.8 billion years old Early atmosphere - CO2, H2O vapor, CO, N2, NH3, H2S, CH4 No O2

Four requirements for formation and accumulation of biomolecules Ch. 21 – Origin and Evolutionary History of Life, pp. 439-441. Four requirements for formation and accumulation of biomolecules - Chemical building blocks - Energy - No O2 - Time Two hypothesis for formation of organic molecules Prebiotic soup/broth Iron-sulfur world

Prebiotic soup On/near earth surface Oparin and Haldane (1920s) Ch. 21 – Origin and Evolutionary History of Life, p. 440. Prebiotic soup On/near earth surface Oparin and Haldane (1920s) Tested by Miller and Urey (1950s) Organic monomers formed polymers on hot rock/clay surfaces

Cracks in deep ocean floor - hydrothermal vents - Hot, CH4, H2S Ch. 21 – Origin and Evolutionary History of Life, pp. 440-442. Iron-sulfur world Cracks in deep ocean floor - hydrothermal vents - Hot, CH4, H2S Laboratory and observational evidence support this hypothesis too How did first cells form from abiotic earth? Protobionts - Abiotically produced - organic polymer assemblages Highly organized, given the simple composition “reproduction” “homeostasis” “metabolism” microspheres (water + synthetic polypeptides) - excitable “Pre-cells” – metabolism first hypothesis

Molecular propagation Ch. 21 – Origin and Evolutionary History of Life, pp. 441-443. Molecular propagation Required for pre-cells to become cells - RNA world - self replicating substrate and enzyme Enzymatic RNA - ribozymes Directed evolution (in vitro) RNA catalyze many bio-reactions RNA DNA Protein

First cells - anaerobic heterotrophic prokaryotes - evidence from Ch. 21 – Origin and Evolutionary History of Life, pp. 443-446. First cells - anaerobic heterotrophic prokaryotes - evidence from microfossils and current stromatolites Depletion/lack of organic molecules - Some survived by obtaining sun’s energy to make ATP First autotrophs used H2S not water for photosynthesis Cyanobacteria - first autotrophs to split water for photosynthesis releasing O2 O2 is poisonous, and aerobes out-competed anaerobes Evolution of aerobic respiration - stabilized CO2 and O2 Formation of O3 layer - land life

Ch. 21 – Origin and Evolutionary History of Life, p. 445.

Cell Theory 1. all organisms are composed of one or more cells 2. cell is the basic unit of structure, function and organization of all organisms 3. all cells come from pre-existing cells/life Discuss connection to evolution in each of 1, 2 and 3 above and thus impact on biology Theodor Schwann (1839 -1&2 above), Matthias Schleiden (1839 -1&2), and Rudolph Virchow (1855 - 3) are credited for formulating the above modern cell theory 17th century - Zacharias Jansen (first compound microscope), Robert Hooke [first to observe (dead) cells], Anton van Leeuwenhoek (first to observe living cells)  Anton van Leeuwenhoek Anton van Leeuwenhoek

Appearance of eukaryotes Contribution by Lynn Margulis Ch. 21 – Origin and Evolutionary History of Life, p. 445-446. Endosymbiont Theory Appearance of eukaryotes Contribution by Lynn Margulis

Picture in an older ed. - Study major Precambrian - 3.8 to .544 bybp Evidence of life not readily abundant, rocks are deep in the earth, volcanoes, mountain rises, pressure/heat destroyed fossils - microfossils, Cnidarians, flat worms Paleozoic - 543 to 252 mybp Algae Gymnosperms Marine invertebrates Insects, reptiles Mesozoic - 251 to 66 mybp Angiosperms, Dinosaurs peak Cenozoic - 65 mybp - extinction of some woody species - Herbaceous plants, Mammals Ch. 21 – Origin and Evolutionary History of Life, p. 446-454. Picture in an older ed. - Study major evolutionary events in the four eras on the left - Table 21-1.