1. Chapter 26 – Early Earth and the Origin of Life

2. History of Earth on a clock… 1 23 4 Billion Years Ago Origin of Earth (4.5 BYA) - Earth Cools(3.9 BYA) Origin of life (3.8 BYA) Origin of Prokaryotes (3.5 BYA) Oxygen in atmosphere (2.7 BYA) Endosymbiosis creates eukaryotic life (2.1 BYA) Multicellular eukaryotic life begins in the sea (1.2 BYA) Marine invertebrates evolve (.54 BYA) Colonization of Land (.5 BYA) Dinosaurs (.1 BYA)Humans (Today)

3. Origin of Earth 4.5 BYA, earth bombarded by rocks  intense heat, no water (evaporated) Primordial atmosphere form due to volcanic activity –Gases released CO, CO 2, H 2, N 2, S, HCL No O 2 No oxygen = “reducing” power To create organic molecules (Spontaneous Synthesis) Back to clock

4. Primordial Seas Earth cools, crust solidifies Water is no longer vaporized, and seas form Back to clock

5. Origin of Life Due to non-oxygenated, reducing atmosphere and energy from lightening, heat, UV rays  small monomers (AA, nucleotides, etc.) randomly assemble (kinetics)  Polymerization occurs, forming macromolecules - RNA = 1st hereditary material (single stranded) - RNA serves as 1st enzymes - Protobionts (membrane droplets) randomly packages organic molecules inside (precursor to cells)

6. Natural selection of protobionts favored those with primitive metabolism and inheritance DNA (double stranded) replaces RNA as hereditary material –DNA more stable –RNA take on more modern roles (translation) Origin of Life Back to clock

7. Origin of Prokaryotes 3.5 BYA 1 st prokaryotes were –anaerobic (no O 2 ) in atmosphere, and –heterotrophic (abundant organic material to be used as food) Back to clock

8. Oxygen in Atmosphere (2.7 BYA) Mutation  heterotrophs gained ability to photosynthesize Oxygen gas generated, ends reducing power of atmosphere Ends of Spontaneous Generation Phase Back to clock

9. Endosymbiosis Creates Eukaryotic Life Mutual symbiosis develop amongst autotrophic and heterotrophic prokaryotes Endocytosis of symbiotic prokaryotes occur Infolding of plasma membrane creates other membrane-bound organelles

10. Endosymbiosis Creates Eukaryotic Life Chloroplasts and Mitochondria Support Endosymbiotic Theory because they - have their own DNA and ribosomes - are similar in size to prokaryotes - self-replicate within eukaryotic cells by binary fission - made up of double membranes, similar in structure to prokaryotes Back to clock

11. Last 1.2 Billion Years Multicellular life in oceans (1.2 BYA) Colonization of Land (.5 BYA) Dinosaurs (.1 BYA) Humans Today