Chapter 25 Systematics 1 Timeline 7 6 bya first animals a 535 mya Cambrian explosion b c 2 1 bya first evidence of eukaryotes d 2 7 bya oxygen producing photosynthesis e 3 5 bya first life evidence of first prokaryotes i Stomatoliths 4 6 bya earth was formed f g 5 bya solar system took form h 10 20 bya Big bang i 2 Prokaryotes 1 2 bya first multicellular eukaryoteslll 500 mya colonization of land a Evidence 3 5 bya dominated until 2 bya b Diversified early into 2 branches domains bacteria and archaea 3 Stromatolites massive calcareous mounds formed by cyanobacteria active or billions of years 4 Evolution of oxygen producing photosynthesis 2 7 bya a Not the first type of photosynthesis i Early forms used H2S as electron source ii O2 producing photosynthesis water is used as the electron source b 2 7 bya O2 O2 increased in water until saturation precipitate of iron oxide settle out banded iron formations i Led to the rise of free O2 in the atmosphere 5 Evolution of Eukaryotes a Fossil evidence 2 1 bya b Molecular evidence 2 7 bya i Could be related to availability of oxygen free c Endosymbiotic bacteria i Precursors of mitochondria allowed the use of oxygen in cellular respiration 6 Multicellular Eukaryotes 1 5 bya a Multiple cells b Cells specialized for specific functions c early embryos 7 First animals a 700 600 mya Precambrian times 8 Cambrian explosion a 535 525 mya b Explosion of animal diversity c All phyla major body plans present at this time i Why so long before diversification of animal body plans 1 snowball Earth Hypothesis a Severe ice age from 750 to 580 mya b Organisms may have been excluded from most areas c Hydrothermal vents refuges 9 Colonization of Land a 500 mya by macroscopic plants animals and fungi b We break up the past into Eras Periods and Epochs HOW i By looking at extinctions c Radiation of animals and plants not gradual punctuated with major changes d Mass extinctions typically follow periods of radiation 10 Mass extinction events a Over a dozen there are five big ones b Mark the boundaries between periods eras etc change in fossils found c 2 largest events i Permian extinctions ii Cretaceous extinctions d Permian extinctions i Permian triassic boundary divides eras palaeozoic mesozoic 1 About 95 of marine animals went extinct less than 5 mya 2 Why a Continental Drift tectonic drift formed Pangea and loss in coastal habitats b Volcanism and methanogen bacteria changed earth s temperature and ocean chemistry ii Changing climate and ocean chemistry 1 Intense volcanism in what is now Siberia increased CO2 in atmosphere and oceans 2 Methanogen bacteria new metabolic mechanism that released methane 3 Global warming and acidification of oceans e Cretaceous Extinctions cretaceous teriary boundary i Loss of the dinosaurs or most birds WHY ii Impact hypothesis meteor strike hit the planet dust cloud cooling extinctions 1 Evidence supporting the impact hypothesis layer of sediment at this geologic boundary enriched with iridium rare on earth common in meteorites Chicxulub crater a For more than 2000 people believed in spontaneous generation life from nonlife i Maggots appeared from manure and frogs and mice from moist earth b Early work in the attempt to disprove this hypothesis i 1668 Frances Redi Italian Physician demonstrated that maggots were larvae of flies and not a product of spontaneous generation ii He placed meat in two jars one covered with fine lace to keep out the flies and the other open the one left open was covered in maggots c Late 18th century Spallanzoni Italian i Heated nutrient broth ii Covered before cooling no microorganisms 11 Origin of Life iii Opened container microorganisms grew iv Others work obtained confliction results they were not convinced and some said that the air was spoiled d 1862 Louis Pasteur French Scientist i Performed several experiments to show that microorganisms come from other microorganisms ii Used a swan necked flask this allowed air into the container but prevented things from falling into it from above iii Boiled media no microbes iv Break top microorganisms grew v 1 Principle of biogenesis Idea that life came from other life became widely accepted 12 When did life arise Have to determine the age of the earth James usher used Hebrew context and estimated the earth was created 4004 BC Lord Kelvin estimated that the earth was formed 20 mya a b c They now estimate the earth to be 4 6 bya 13 Conditions on primitive earth a At time of life s origin atmosphere was very different from now b Reducing Environment no free oxygen c No UV shield i Methane carbon dioxide ammonia water vapor nitrogen hydrogen ii Water condensed as earth cooled precipitation oceans filled 14 How did life arise need formation of organic molecules a Hypothetical scenario involves 4 stages i The abiotic synthesis of small organic molecules contain carbon formerly thought to be only of biological origin Joining these small molecules into polymers ii iii Origin of self replicating molecules iv Packaging of these molecules into protobionts 15 Abiotic synthesis of organic molecules a No free o2 energy from lightning strikes b No ozone layer UV shield more light energy c Conditions today differ would prevent this from occurring 16 1953 Stanley Miller graduate student performed landmark experiment a Mimic the conditions of the atmosphere when life evolved b Established a reducing atmosphere no free oxygen c Passed the gases over a spark to simulate lightning i Results 1 Few hours system contained numerous simple organic compounds including amino acids polymers proteins 2 Synthesis occurred under a variety of conditions as long as o2 was absent 3 Compounds could have also reacted With HCN to form based of nucleotides and subunits of nucleic acids DNA RNA 17 RNA first catalyst enzyme a Dna to mrna to proteins b It was originally thought that proteins were the first catalysts 18 Which came first Protein or nucleic acids a Scientists working with Tetrahymena thermophile a unicellular protist b Showed that RNA rather than ribosome protein catalyzed protein synthesis i Ribozymes RNA that catalyze reactions 1 ribosomes translation has protein and RNA components 19 Which was the first nucleic acid RNA a RNA is thought to have evolved first first information carrying molecule replicated themselves b RNA monomers short strands were copied i zinc larger sequences were copies Some functions taken over by proteins once they evolved more efficient c d RNA can