History of Life on Earth - Student Notes PDF

H I S T O RY O F LIFE ON E A RT H Dr. Szuroczki Chapter 26 Key Concepts 1. Origin of Life on Earth (not found in text) 2. The Fossil Record 3. History of Life on Earth 4. Human Evolution (briefly) Life on Earth The Earth is believed to have formed from the aggregation of planetesimal...

H I S T O RY O F LIFE ON E A RT H Dr. Szuroczki Chapter 26 Key Concepts 1. Origin of Life on Earth (not found in text) 2. The Fossil Record 3. History of Life on Earth 4. Human Evolution (briefly) Life on Earth The Earth is believed to have formed from the aggregation of planetesimals ~4.55 BYA By 4 BYA the outer layers had cooled enough to solidify and accumulate liquid water Life emerged between 4 and 3.5 BYA Key players in all life – Central dogma Four stage process Nucleotides and amino acids were 1 produced prior to cells Nucleotides became polymerized to form RNA and/or DNA, and 2 amino acids became polymerized to form proteins Polymers became enclosed in 3 membranes Polymers enclosed in membranes 4 acquired cellular properties  1 Formation of organic molecules Organic molecules and macromolecules formed spontaneously and slowly accumulated in early oceans = Prebiotic soup How and where did this soup originate? 1. Reducing atmosphere hypothesis 2. Extraterrestrial hypothesis 3. Deep-sea vent hypothesis 1. Reducing atmosphere hypothesis Based on geological data, early Earth atmosphere was rich in water vapour (H2O), H2, CH4, NH3, with little O2 Favours redox reactions required for formation of complex organic molecules Tested experimentally by Miller and Urey in 1953 System formed precursor molecules, amino acids, sugars, nitrogenous bases Other gas mixtures performed similarly 2. Extraterrestrial hypothesis Meteorites brought organic carbon to Earth Carbonaceous chondrites contain a substantial amount of organic carbon Includes amino acids and nucleic acid bases Opponents argue that most of this would be destroyed in the intense heating and collision 3. Deep-sea vent hypothesis Biologically important molecules may have formed in the temperature gradient between extremely hot vent water and cold ocean water Supported by experiments showing formation of NH3 in these conditions Key component of amino acids and nucleic acids  2 Formation of organic polymers Prebiotic synthesis of polymers is generally believed to be unlikely in aqueous solutions Hydrolysis competes with polymerization Proposed to have taken place on clay Interaction between cations on clay surface (e.g. Mg2+) and nucleotides could help promote bond formation Supported by experiments showing formation of polypeptides and nucleic acid polymers on clay surface However, recent work has shown that carbonyl sulfide can produce aqueous conditions that leads to formation of polymers in water  3 Formation of cell-like structures Protobiont: An aggregate of prebiotically produced molecules and macromolecules that have acquired a boundary, such as a lipid bilayer Allows it to maintain an internal chemical environment distinct from that of its surroundings Four characteristics of a protobiont: 1. A boundary separating external environment from internal contents 2. Polymers inside containing information 3. Polymers inside with enzymatic function 4. Capable of self-replication Living cells may have evolved from Coacervates Droplets that form spontaneously from the association of charged polymers such as proteins, carbohydrates, or nucleic acids surrounded by water Enzymes trapped inside can perform primitive metabolic functions Skin of water allows selective absorption of simple molecules from surrounding medium Living cells may have evolved from Liposomes Vesicles surrounded by a phospholipid bilayer Clay can catalyze formation of liposomes that grow and divide If RNA is on clay surface, liposomes enclosing RNA will form  4 Acquisition of cellular characteristics Majority of scientists favor RNA as the first macromolecule of protobionts Three key RNA functions: 1. Ability to store information 2. Capacity for self-replication 3. Enzymatic function (ribozymes) DNA and proteins cannot do all 3 functions! How did first RNA molecules produce cell-like characteristics? Chemical selection: Occurs when a chemical within a mixture has special properties that cause it to increase in number compared to other chemicals in the mixture Hypothetical two-step scenario: 1. One of the RNA molecules mutates and acquires enzymatic ability to self-replicate RNA 2. Second mutation produces enzymatic ability that promotes synthesis of ribonucleotides Would no longer rely on slow prebiotic synthesis  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. First step of chemical selection 1a Mutation: A mutation provides an RNA molecule with the catalytic ability to synthesize new RNA molecules using pre-existing RNA molecules as templates. RNA A protobiont with no catalytic functions Mutant RNA with catalytic ability to self-replicate RNA  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. First step of chemical selection 1a Mutation: A mutation provides an RNA molecule with the catalytic ability to synthesize new RNA molecules using pre-existing RNA molecules as templates. RNA A protobiont with no catalytic functions Mutant RNA with catalytic ability to self-replicate RNA 1b Chemical selection: The amount of this mutant RNA with catalytic function increases because it can self-replicate faster. A protobiont with 1 catalytic function  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. First step of chemical selection Second step of chemical selection 1a Mutation: A mutation provides an RNA molecule with the 2a Mutation: A second mutation provides an RNA catalytic ability to synthesize new RNA molecules using molecule with the ability to catalyze a step in pre-existing RNA molecules as templates. the synthesis of ribonucleotides. RNA A protobiont with no catalytic functions Mutant RNA with catalytic ability to self-replicate RNA Mutant RNA with the 1b Chemical selection: ability to catalyze a The amount of this mutant step in the synthesis of RNA with catalytic ribonucleotides function increases because it can self-replicate faster. A protobiont with 1 catalytic function  Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. First step of chemical selection Second step of chemical selection 1a Mutation: A mutation provides an RNA molecule with the 2a Mutation: A second mutation provides an RNA catalytic ability to synthesize new RNA molecules using molecule with the ability to catalyze a step in pre-existing RNA molecules as templates. the synthesis of ribonucleotides. RNA 2b Chemical selection: The second mutation is also favoured, so after many A protobiont with no generations, the protobionts catalytic functions have 2 catalytic functions— self-replication and ribonucleotide synthesis. Mutant RNA with catalytic ability to self-replicate RNA Mutant RNA with the 1b Chemical selection: ability to catalyze a The amount of this mutant step in the synthesis of RNA with catalytic ribonucleotides function increases because it can self-replicate faster. A protobiont with 1 A protobiont with 2 catalytic function catalytic functions RNA world Hypothetical period on early Earth when the information needed for life and the catalytic activity of living cells was contained solely in RNA molecules Over time, mutation and chemical selection would producing increasing complexity Superseded by modern DNA/RNA/protein world Advantages of DNA/RNA/protein world Information storage Incorporation of DNA to store information would relieve RNA of this function, and allow RNA to perform more complex catalytic functions DNA has increased stability Ancestral RNA may have been able to make DNA from RNA template Metabolism and other cellular functions Proteins have vastly greater catalytic potential Proteins can perform other tasks – structural, transport, etc. Ancestral RNA likely contributed to polypeptide formation Still plays central role in protein synthesis! The origin of life Lines of Evidence: Fossils Preserved remains of past life on Earth Studied by paleontologists Usually formed within sedimentary rock Organisms buried quickly in gravel, sand or mud Over time, more layers pile up and sediments at bottom become rock Over millions of years, hard parts are replaced by minerals, producing a representation of original organism Layers of sedimentary rock Lower layers are older than upper layers  Lycopod tree embedded in Joggins Cliffs (NS) Extremely well-preserved Feather in Coprolites from Kap Borealopelta markmitchelli amber Stewart formation in 25 discovered in Fort McMurray Greenland Radioisotope dating Fossil age is estimated by radiometric dating Measures the amount of a radioisotope and its decay product in the accompanying rock Each radioisotope has a unique half-life that can be used for dating = time required for exactly one-half of original isotope to decay Usually igneous rock in vicinity of sedimentary rock is dated Rock formed from lava Initially contains uranium-235 but no lead-207 (decay product) Factors that affect the fossil record History of Life on Earth Geological timescale: A timeline of Earth’s history from its origin until the present The Earth’s timeline from 4.55 BYA to present is subdivided into four eons, then further subdividedPrecambrian into eras Hadean Archaean Proterozoic Phanerozoic History of life on earTH Changes in living organisms are the result of two interactive processes: Genetic changes Affects an organism’s characteristics Influences ability to survive and reproduce in native environment Environmental changes Dramatic changes over 4 billion years Can allow new types of organisms to flourish Can lead to extinction If many species are affected = mass extinction Mass extinctions Major environmental changes 1. Temperature: 2.5 billion years of cooling, followed by 2 billion years of major fluctuations 2. Atmosphere: Changes in gas composition Especially oxygen increase beginning 2.4 bya 3. Landmasses: Formation of landmasses surrounded by water, and shifting of continents over time Major environmental changes 4. Floods and glaciations: Periodic catastrophic floods and glaciers moving across continents 5. Volcanic eruptions: Can kill organisms, form islands, alter atmosphere 6. Meteoric impacts: Many during Earth’s history Archaean Eon Period from ~3.8 to 2.5 bya, characterized by diverse microbial life flourishing in primordial oceans All life forms were prokaryotic and anaerobic Atmosphere contained very little free O2 Two domains of prokaryotic life diverged quite early Archaea and bacteria Heterotrophs vs Autotrophs Two mechanisms of obtaining energy: Heterotrophs: Derive energy from chemical bonds within organic molecules that are consumed. Autotrophs: Directly harness energy from inorganic molecules or light. Heterotrophs were likely first, and consumed organic molecules left in prebiotic soup As this energy source dwindled, autotrophs evolved Why are earliest fossils cyanobacteria (autotrophs)? Their growth forms stromatolites, which make good fossils! Stromatolites Certain autotrophic cyanobacteria form stromatolites – layered structure of calcium carbonate Cyanobacteria produce organic molecules from CO2 Also produce oxygen as a waste product of photosynthesis Spelled doom for many prokaryotic groups that were anaerobic Allowed the evolution of aerobic species Rising oxygen Proliferation of ancient cyanobacteria: Produced new source of organic molecules from CO2 Produced O2 as a waste product of photosynthesis Anaerobic species were killed off, or become restricted to anoxic environments Paved way for aerobic respiration and emergence of eukaryotes Proterozoic Eon: Endosymbiotic origin of eukaryotes Any organism that lives within the body or cells of another organism most often, though not always, in a mutualistic relationship Some live intra-cellularly: Paramecium and Chlorella Paramecium shields algae Algae provide nutrients Paramecium can digest algae if necessary Proterozoic Eon: Endosymbiotic origin of eukaryotes 1970 Lynn Margulis, argued that organelles evolved from a symbiotic relationship between 2 prokaryotic cells Endosymbiosis: within, beneficial relationship Endosymbiont: provided resources (energy or food Host: provided protection from the environment Over time it developed into an obligate relationship 38 Proterozoic Eon: Endosymbiotic origin of eukaryotes Multicellular Eukaryotes Arose ~1.5 bya during Proterozoic eon Oldest fossil = 1.2 billion years old, resembles red algae Two possible origins: 1. Individual cells aggregated to form a colony 2. Cells stuck together after dividing Variation in multicellulari ty in related green algae species 3 major lineages of cells arose from the microbial ancestors All cells are descended from a common ancestral cell = Last universal common ancestor (LUCA) Cells have been evolving for nearly 4 billion years Three major cell lineages (domains) can be distinguished: Bacteria, Archaea, and Eukarya Bacteria and Archaea are phylogenetically distinct Archaea are more closely related to Eukarya than Bacteria  Proterozoic Eon: Multicellular animals Emerged toward the end of the Proterozoic eon (632 mya) First animals were invertebrates (no backbone) Earliest known ancestor of animals with bilateral symmetry may be Vernanimalcula guizhouena 580 – 600 mya fossil from China Phanerozoic Eon 543 mya to today Proliferation of multicellular eukaryotic life extensive Includes three eras further subdivided into periods Phanerozoic Eon Paleozoic Era Cambrian Period 543-490 mya Warm and wet with no ice at poles Characterized by Cambrian explosion Abrupt increase in diversity of animal species By mid-period, all existing major types of marine invertebrates were present, plus many other that no longer exist Echinoderms, arthropods, mollusks, and chordates First vertebrates ~520 mya Burgess Shale Rock bed in Canadian Rockies that produced an abundance of fossils from the Cambrian period Underwater mudslide preserved even soft tissues Causes of Cambrian Explosion 1. Evolution of shells allowed animals to exploit new environments 2. Increase in atmospheric oxygen levels allowed for more complex body plans Production of ozone layer helped screen UV radiation 3. Evolutionary arms race between predators and prey  Phanerozoic Eon Paleozoic Era Ordovician Period 490 - 443 mya Trilobites (now extinct) and brachiopods are abundant in the fossil record Hard-shelled marine invertebrates First invasion of early land plants and arthropods Toward end of period, drastic climate change occurred Large glaciers formed, draining the oceans Triggered mass extinction of ~60% of marine invertebrates  Phanerozoic Eon Paleozoic Era Silurian Period 443 – 417 mya Relatively stable climate Melting of glaciers increased ocean levels New fishes, appearance of coral reefs Significant new vertebrates and plants Major colonization of land by terrestrial plants and animals Adaptations that prevented drying out (e.g. external cuticle) Earliest fossils of vascular plants  Phanerozoic Eon Paleozoic Era Devonian Period 417 – 353 mya Generally dry across northern landmasses, but southern hemisphere mostly covered by cool, temperate oceans Major increase in the number of terrestrial species Ferns, horsetails, and gymnosperms (seed plants) emerge First trees and forests formed by end of period Insects and tetrapods came into existence In oceans invertebrates and fish flourish Near end, prolonged series of extinctions eliminate many marine species Tetrapod evolution Tiktaalik “fishapod” Shares anatomical features with both primitive fish and tetrapods Ichthyostega Four limbs with increased adaptations for survival on land Dragged itself forwards using strong front limbs Phanerozoic Eon Paleozoic Era Carboniferous Period 354 – 290 mya Cooler land covered by forested swamps Rich coal deposits formed Plants and animals further diversified Very large plants and trees First flying insects Amphibians prevalent Emergence of reptiles  Phanerozoic Eon Paleozoic Era Permian Period 290 – 248 mya Continental drift formed supercontinent Pangea Interior regions dry with seasonal fluctuations Forest shift to gymnosperms with emergence of conifers Reptiles dominate and first mammal- like reptiles appear Robertia At the end of period, largest known mass extinction event eliminated 90 – 95% of marine species and large proportion of terrestrial species Due to glaciations or volcanic eruptions Transition to Mesozoic Era The Permian extinction marks boundary between Paleozoic and Mesozoic eras Mesozoic = “middle animals” The Age of Dinosaurs Consistently hot climate, dry terrestrial environments, little if any ice at poles  Phanerozoic Eon Mesozoic Era Triassic Period 248 – 206 mya Reptiles plentiful New groups: crocodiles & turtles Emergence of first dinosaurs and mammals Gymnosperms dominant land plant Megazostrodon Volcanic eruptions led to global warming and mass extinctions near end of period Phanerozoic Eon Mesozoic Era Jurassic Period 206 – 144 mya Gymnosperms continued to be dominant vegetation Reptiles dominant land animal Some dinosaurs attained enormous size First known bird Mammals present but not prevalent Archaeopteryx 55 Archaeopteryx  Phanerozoic Eon Mesozoic Era Cretaceous Period 144 – 65 mya Earliest flowering plants, angiosperms, emerged and began to diversify Dinosaurs still dominant on land Another mass extinction at end of period Dinosaurs and many other species died out Large meteorite/asteroid and/or volcanic eruptions blamed Transition to Cenozoic Era Spans most recent 65 million years Tertiary and quaternary periods Tropical conditions replaced by a colder, drier climate Mammals became largest terrestrial animals Sometimes called The Age of Mammals Amazing diversification of birds, fish, insects, and flowering plants Phanerozoic Eon Cenozoic Era Tertiary Period 65 – 1.8 mya Angiosperms became dominant land plant Insects important for pollination Surviving mammals expanded rapidly Fish diversified and sharks became abundant Hominoids appeared ~7 mya Australopithecus Includes humans, chimpanzees, gorillas, orangutans, and gibbons plus their recent ancestors  Phanerozoic Eon Cenozoic Era Quaternary Period 1.8 mya – present Periodic ice ages cover Homo habilis much of Europe and North America Widespread extinction of many species of mammals Certain hominins become more like living humans Homo Homo sapiens appear neanderthalensi s 170,000 years ago  A E History of Life st fir Concept Map B F G f re d so cu r ist Origin of oc ons st earth ____ bya c 4 ____ C fir H I M st Word list for A - Q: J fir N Prokaryotic cells Reptiles of Dinosaurs Phanerozoic sis ts O n Land plants Multicellular eukaryotes D co 3 ____ nvertebrates Cenozoic : of Paleozoic Mammals Ag e K P No life Hadean Tetrapods Archaean : Eukaryotic cells Proterozoic e of Ag L Q  Hadean No Life History of Life st Concept Map Archean fir Prokaryotic cells Eukaryotic cells ed s of r ur ist Origin of oc c n s t Multicellul __4.55 bya co 4 __Eons__ Proterozoic firs ar earth eukaryotes Invertebrat es Land plants st Tetrapods Word list for A - Q: Paleozoic fir Prokaryotic cells Reptiles of Dinosaurs Phanerozoic sis ts Reptiles n Land plants Multicellular eukaryotes Phanerozoi co 3 _eras___ c nvertebrates Cenozoic : of Paleozoic Mammals Ag e Mesozoic Dinosaurs No life Hadean Tetrapods Archaean : Eukaryotic cells Proterozoic e of Ag Cenozoic Mammals