Ch. 26: The Origin and Diversity of Life -Deep Time o 4 eons are divided into eras which are divided into periods o Hot mass of molten rock about 4.6 BYAMantle melted, Hadean Earth hit with asteroids, cool and formed oceans through water condensation o CO2 levels were high and water slowly vaporized from molten rock o Increase weathering silicate rock soil CO2 carbonic acid Carbonic acid bicarbonate ions from rocks o Decreases in CO2 lowered temperature o Crust moved and formed plates o Supercontinents Rodinia all continentsGondwana all Southern Hemisphere continents Pangea formed from Gondwana o Life during the Archean eon Proterozoic -2 BY into history -formation of Rodinia o breaks up during eonCambrian period showed diversification of multicellular -The Past Can Be Reconstructed from the Fossil Record o Fossils are preserved remains o Rock fossils are created when… Organism buried in sedimentCalcium mineralizesSurrounding sediment hardens to form rock RARE -Aging Fossils o Relative Age: position of the fossil in the sedimento Absolute Age: estimated by rates of radioactive decay-Absolute Age o Isotopes transform at precise rates o Half life: amount of time needed for ½ of the original amount to be transformed o Potassium isotopes: 1.25 BY half lifeo Carbon isotopes: 5700 BY half life -Conditions on Early Earth o First organisms at very high temperatures 3.8 to 2.5 BYA o Early atmosphere: could have been reducing for carbon-rich molecules-Organic Molecules May Have Originated on Early Eartho Popular view on early atmosphere CO2, N2, H2O, H2, sulfur, nitrogen, and carbon compounds, but no O2o Miller and Urey experiment Assembled reducing atmosphere, placed over water, simulated lightning with sparks Within a week, methane converted to other carbon compounds Later experiments produced 30+ compounds including amino acids o RNA may have been first genetic material o Amino acids polymerized to proteins Organisms may have been autotrophico Lipid bubbles increased probability of metabolic reactions lead to cell membranes o Other innovations contributed to diversity -The First Cell o Microfossils fossilized form of microscopic life 3.5 BY old at oldest resembling modern prokaryotes o stromatolites: mats of cyanobacterial cells trapping mineral deposits oldest are 2.7 BY with some modern forms o living things selective about carbon; Carbon 12 analysis in fossils suggests fixation was active 3.8 BYAo Biomarkers Organic markers of biological origin Hard to findHydrocarbons derived from fatty acids from lipids in old rockPossible origin of life pushed beyond 3.5 BYA -Earth’s Changing System o Dramatic shifts in climate and atmosphere caused mass extinctions and influence evolution Cooling since formationExtreme drops in temperature cause ice ageso Continental motion affected evolutiono Cenozoic era began 65 MYA Australia and Antarctica separateGreenland and North America separateAtlantic ocean grew Greenhouse conditions during Cretaceous period rose sea levels and some continental areas were submerged Photosynthesis begins producing atmospheric O2200 MY between origins of photosynthesis and substantial O2-iron oxide in oceans -O2 in atmosphere interacted for UV and formed O3Growing evidence that plants contributed to ice ages -Colonization of land by plants was followed by abrupt cooling period -Vascular plant diversification concurrent with second ice age -Ever-Changing Life on Earth o Evolved into 3 monophyletic domains Eubacteria, Archaea, Eukaryotes 6 supergroups within Eukaryote -Chromalveolates, Rhizaria, Archaeplastida, Excavata, Amoebozoa, Opisthokorta 3 domain system: Archaea, Bacteria, Eukarya-Compartmentalization of Cells o Enabled advent of eukaryotes Bacteria and archaea ruled for 1 BY -Lack compartmentalization Eukaryotes endomembrane system -Nuclear membrane increased complexity -Physical separation of transcription and translation-Golgi apparatus and endoplasmic reticulum facilitate intracellular transport Endosymbiosis -Mitochondria and chloroplast enter cells through endosymbiosis -Mitochondria are descendants of sulfur bacteria and rickettsia -Chloroplasts derived from cyanobacteria -Multicellularity Leads to Cell Specialization o Unicellular prokaryotes and eukaryotes constitute ½ biomass on eartho Multicelluarlity allows dealing with environment through differentiation -Sexual Reproduction Increases Genetic Diversity o Meiosis, crossing over o First eukaryotes were probably haploido Diploids arose later, possibly through fusion of haploids -Rapid Diversification Occurred During Cambrian o Evolutionary innovations while life was aquatic Foundations for diversityRadiation confined to oceansFirst multicellular organisms 50 years following Cambrian radiation-Major Innovations Allowed for the Move Onto Land o Plants and animals colonized land after Cambrian radiationo Evolution of photosynthesiso Ozone layer protects from UV light -Key Eukaryotic Characteristics o CompartmentalizationIncreased subcellular specialization Nuclear membrane additional levels of control of transcription/translation o Multicellulairty: differentiation of cells into tissues o Sexual reproduction: greater genetic diversity -Naming Diverse Organisms is Essential to Biology o Shift from emphasis on identifying to construction evolutionary hypotheses to explain relatednesso Organisms grouped into taxa: kingdom, phylum, class, order, family, genus,
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