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“…sparked by just the right combination of physical events & chemical processes…” Origin of Life AP Biology 2007-2008 Millions of years ago 1000 1500 2000 2500 3000 3500 Paleozoic PROTEROZOIC PRECAMBRIAN 500 Cenozoic Mesozoic ARCHEAN 0 Colonization of land by animals Appearance of animals and land plants First multicellular organisms Animalia Oldest definite fossils of eukaryotes Appearance of oxygen in atmosphere Oldest definite fossils of prokaryotes 4000 Molten-hot surface of earth becomes cooler 4500 Formation of earth AP Biology Bacteria Archae- Protista Plantae Fungi bacteria The evolutionary tree of life can be documented with evidence. The Origin of Life on Earth is another story… What is Life? First we have to define LIFE… organized as cells respond to stimuli regulate internal processes homeostasis use energy to grow metabolism develop change & mature within lifetime reproduce heredity DNA / RNA adaptation & evolution AP Biology The Origin of Life is Hypothesis Special Creation Was life created by a supernatural or divine force? not testable Extraterrestrial Origin Was the original source of organic (carbon) materials comets & meteorites striking early Earth? testable Spontaneous Abiotic Origin AP Biology Did life evolve spontaneously from inorganic molecules? testable Conditions on early Earth Reducing atmosphere water vapor (H2O), CO2, N2, NOx, H2, NH3, CH4, H2S lots of available H & its electron low O2 = no free oxygen Energy source lightning, UV radiation, volcanic What’s missing from that atmosphere? AP Biology organic molecules do not breakdown as quickly Electrodes discharge sparks (lightning simulation) Origin of Organic Molecules Abiotic synthesis 1920 Oparin & Haldane propose reducing atmosphere hypothesis 1953 Miller & Urey test hypothesis Water vapor CH4 NH3 Mixture of gases ("primitive atmosphere") H2 Condenser Water formed organic compounds amino acids adenine AP Biology Heated water ("ocean") Condensed liquid with complex, organic molecules Stanley Miller University of Chicago produced -amino acids -hydrocarbons -nitrogen bases -other organics It’s ALIVE! AP Biology Origin of Cells (Protobionts) Bubbles separate inside from outside metabolism & reproduction Different types: Liposomes(split), Proteinoids(can have a charge) Bubbles… Tiny bubbles… AP Biology Dawn of natural selection Origin of Genetics RNA is likely first genetic material multi-functional codes information self-replicating molecule makes inheritance possible natural selection & evolution enzyme functions Ribozymes(RNA catalyst) Control replication of various RNA strands ex. tRNA & mRNA regulatory molecule transport molecule AP Biology Key Events in Origin of Life Key events in evolutionary history of life on Earth AP Biology life originated 3.5–4.0 bya Prokaryotes Prokaryotes dominated life on Earth from 3.5–2.0 bya 3.5 billion year old fossil of bacteria AP Biology modern bacteria chains of one-celled cyanobacteria Lynn Margulis Stromatolites Fossilized mats of prokaryotes resemble modern microbial colonies AP Biology Oxygen atmosphere Oxygen begins to accumulate 2.7 bya reducing oxidizing atmosphere evidence in banded iron in rocks = rusting makes aerobic respiration possible AP Biology photosynthetic bacteria (blue-green algae) ~2 bya First Eukaryotes Development of internal membranes create internal micro-environments advantage: specialization = increase efficiency natural selection! infolding of the plasma membrane plasma membrane endoplasmic reticulum (ER) nuclear envelope nucleus DNA cell wall Prokaryotic cell AP Biology Prokaryotic ancestor of eukaryotic cells plasma membrane Eukaryotic cell Endosymbiosis Evolution of eukaryotes origin of mitochondria engulfed aerobic bacteria, but did not digest them mutually beneficial relationship natural selection! internal membrane system aerobic bacterium mitochondrion Endosymbiosis Ancestral AP Biology eukaryotic cell Eukaryotic cell with mitochondrion Endosymbiosis Evolution of eukaryotes Eukaryotic cell with mitochondrion origin of chloroplasts engulfed photosynthetic bacteria, but did not digest them mutually beneficial relationship natural selection! photosynthetic bacterium chloroplast Endosymbiosis Eukaryotic cell with AP Biology chloroplast & mitochondrion mitochondrion Theory of Endosymbiosis Evidence structural Lynn Margulis mitochondria & chloroplasts resemble bacterial structure (inner membrane has enzymes and transport systems like plasma membrane of eukaryotes) genetic mitochondria & chloroplasts have their own circular DNA, like bacteria functional mitochondria & chloroplasts AP Biology move freely within the cell mitochondria & chloroplasts reproduce independently from the cell(binary fission) Cambrian explosion Diversification of Animals 543 mya AP Biology within 10–20 million years most of the major phyla of animals appear in fossil record AP Biology AP Biology Diversity of life & periods of mass extinction Cambrian explosion AP Biology Cretaceous extinction The Chicxulub impact crater in the Caribbean Sea near the Yucatan Peninsula of Mexico indicates an asteroid or comet struck the earth and changed conditions 65 million years ago AP Biology Early mammal evolution 125 mya mammals began to radiate out & fill niches AP Biology Classifying Life Molecular data challenges 5 Kingdoms Monera was too diverse 2 distinct lineages of prokaryotes Protists are still too diverse not yet sorted out AP Biology 3 Domain system Domains = “Super” Kingdoms Bacteria Archaea extremophiles = live in extreme environments Methanogens:H2 is used to reduce CO2 into methane Halogens: live in extreme salt Thermophiles: live in extreme heat ex. Sulfur springs in Yellowstone, deep sea vents AP Biology Eukarya eukaryotes protists fungi plants animals Kingdom Bacteria Kingdom AP BiologyFungi Kingdom Archaebacteria Kingdom Protista Kingdom Plantae Kingdom Animalia Four Groups of Prokaryotes(based on energy and Carbon source) Photoautotrophs: harness light energy to synthesize organic compounds Ex. Cynobacteria Chemoautotrophs: need only CO2 as a carbon source, get energy by oxidizing inorganic. substances(Hydrogen Sulfide, ammonia, ferrous ions) ex. Bacteria of nitrogen cycle(denitrifying bacteria). Photoheterotrophs: use light to generate ATP but must get carbon from organic materials. Ex. heliobacteria Chemoheterotrophs: consume organic compounds for energy and carbon. Ex. Saprobes, parasites AP Biology Any Questions?? Is there life elsewhere? Does it look like life on Earth? AP Biology 2008-2009