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BIO1130 - Cambrian and Ordovician Periods 1.docx

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Cambrian and Ordovician PeriodsNearEnd Proterozoic 2 Billion Years as Single Celled ProtistsExplosion of unicellular life some bigger than othersContinental land masses arising from ocean near end of Proterozoic Massive flourishing of invertebratesoConsumed carbon dioxide therefore carbon dioxide levels decreaseWhy Did it take 3 Billion years for multicellular life to originateSomething changed in the ancient oceans filled with bacteria single celled protists etcSnowball Earth 2 or 3 cycles had occurred during earths lifetimeEarth was completely covered by ice and snowNo primary productivity during this time periodoUnderneath ocean still getting volcanic gases sulphur gasesHydrothermal vents extremophiles low oxygen environmentsImpossible for multicellular life to beginSlushball Earth more likely theoryNear equator there is a slushy icy thingsoAllows some of the aerobic protists and bacteria to form and survive Earth was frozen over however near the equator it was much warmer allowing more forms of life to form thereDoushantuo Fossils found in ChinaSpherical in shape Looks like zygote The thought is that these fossils represent fossilized embryosoAre they evidence of multicellular life or just bacterial aggregatesWe dont knowPrior to CambrianEdiacaran Fossils found in New Found LandPredate the CambrianExperiments in multicellular life before Cambrian Only a hypothesisFossilized sponges evidence that sponges DID exist oSpongesfiltration of water to trap protists archae bacteria ect because the ocean was a souplots of foodoColonial Choanoflagellates are the types of organisms that are seen in Ediacaran FossilsVery first multicellular organisms that are trapping foodEctodermOutermost layer forms external covering and nervous systemMesodermMiddle layerform muscles of body wall and other structures between gut and external covering Germ LayersEndodermInnermost layerforms lining of gut some organisms respiratory organsEdiacaran PeriodChoanocyteoUses a single Flagellum animallikeWhen it beats spiral it propels water away from the spongeWater passes series of microvilli acts as filterPhagocytosis to feedlike an animaloCollar cells of sponges individual cellsColonial Choanoflagellates Group of Choanocytes working togetheroSaid to be the first experiments of multicellularityoCluster of cells on a single stalk sessile
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