Download Phanerzoic Eon, Paleozoic Era

CHAPTER 22:ORIGIN AND HISTORY OF LIFE
 The universe began with the Big Bang about 13.7 bya
 Our solar system began about 4.6 bya
 The Earth is 4.55 billion years old
 4 bya the Earth cooled enough for outer layers to solidify and oceans to form
 4-3.5 bya life emerged
Origin in 4 overlapping stages
 Nucleotides and amino acids produced prior to the existence of cells
 Nucleotides and amino acids became polymerized to form DNA, RNA and proteins
 Polymers became enclosed in membranes
 Polymers enclosed in membranes evolved cellular properties
Stage 1: Origin of organic molecules
 Conditions on primitive Earth may have been more conducive to spontaneous formation of
organic molecules
 Prebiotic or abiotic synthesis
 Formed prebiotic soup
 Several hypotheses on where and how organic molecules originated
 Reducing atmosphere hypothesis
 Based on geological data
 Experiments simulated conditions of primitive Earth postulated in 1950s
 Formed precursors, amino acids, sugars and nitrogenous bases
 First attempt to apply scientific experiments to understand origin of life
 Since 1950s, ideas about early Earth atmosphere changed
 Similar results
 Extraterrestrial hypothesis
 Meteorites brought organic carbon to Earth
 Includes amino acids and nucleic acid bases
 Opponents argue that most of this would be destroyed in the intense heating and collision
 Deep-sea vent hypothesis
 Biologically important molecules may have been formed in the temperature gradient between
extremely hot vent water and cold ocean water
 Supported by experiments
 Complex biological communities found here that derive energy from chemicals in the vent (not
the sun)
Stage 2: Organic polymers
 Experimentally, prebiotic synthesis of polymers not possible in aqueous solutions
 Experiments have shown formation of nucleic acid polymers and polypeptides on clay surface
Stage 3: Formation of boundaries
 Protobiont/ prebiont describes first nonliving structures that evolved into living cells
 4 characteristics
 Boundary separated external environment from internal contents
 Polymers inside the protobiont contained information
 Polymers inside the protobiont had enzymatic function
 Protobionts capable of self-replication
Living cells may have evolved from
 Coacervates
 Droplets that form spontaneously from the association of charged polymers
 Enzymes trapped inside can perform primitive metabolic functions
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 Microspheres
 Small
water-filled vesicles surrounded by a macromolecular boundary
 Liposomes
 Vesicles surrounded by a lipid layer
 Clay can catalyze formation of liposomes
 Can enclose RNA
that grow and divide
Stage 4: RNA world
 Majority of scientists favor RNA as the first macromolecule of protobionts
 3 key RNA functions
 Ability to store information
 Capacity for replication
 Enzymatic function – ribozymes
 DNA and proteins do not have all 3 functions
Chemical selection
 Chemical within a mixture of different chemicals has special properties or advantages that cause
it to increase in number compared to other chemicals in the mixture
 Hypothetical scenario with 2 steps
 One of the RNA molecules mutates and has enzymatic ability to attach nucleotides together
 Advantage of faster replication
 Second mutation produces enzymatic ability to synthesize nucleotides
 No reliance on prebiotic synthesis
Bartel and Szostak Demonstrated Chemical Selection in the Laboratory
 Began with synthesis of 1015 RNA molecules (long)
 Each RNA contained 2 regions – constant region the same in all the molecules and a variable
region
 Also made short RNAs that were complementary to a portion of the long RNA and had a tag
sequence to bind to beads
 If the long RNAs mutated and obtained enzymatic activity, the long RNA would be held to the short
RNA bound to the beads
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Long RNAs that had this ability formed pool #1
More long RNAs were made that were variations on Pool #1
Repeated several times
Pool #10 showed enzymatic ability 3 million times higher that the original random pool
Results showed that chemical selection improves the functional characteristics of a group of RNA
molecules over time by increasing the proportions of those molecules with enhanced function
Advantages of DNA/RNA/protein world
 Information storage
 DNA would have relieved RNA of informational role and allowed RNA to do other functions
 DNA is less likely to suffer mutations
 Metabolism and other cellular functions
 Proteins have a greater catalytic potential and efficiency
 Proteins can perform other tasks – cytoskeleton, transport, etc.
History of life on Earth
 Geological time scale
 Origin 4.55 bya to present
 Precambrian- first 3 eons
 Changes in living organisms the result of
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 Genetic changes
 Environmental changes
Can allow for new types of organisms
 Responsible for many extinctions
Major environmental changes
 Climate/temperature
 Atmosphere
 Land masses
 Flood
 Glaciation
 Volcanic eruptions
 Meteoric impacts
Mass extinctions
 5 large mass extinctions
 Near end of Ordovician, Devonian, Permian, Triassic, and Cretaceous periods
 Geologic time periods are often based on these events
Fossils
 Recognizable remains of past life on Earth
 Paleontologists study fossils
 Many rocks with fossils are sedimentary
 Sediments pile up and become rock
 Organisms buried quickly and hard parts replaced by minerals
 Older rock is deeper and older organisms are deeper in the rock bed
Radioisotope dating
 Fossils can be dated using elemental isotopes in accompanying rock
 Half-life – length of time required for exactly one-half of original isotope to decay
 Measure amount of a given isotope as well as the amount of isotope produced when the isotope
decays
 Usually igneous rock dated
 Expect fossil record to underestimate actual date species came into existence
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Prokaryotic cells arose during Archaeon Eon
 Archaeon Eon when diverse microbial life flourished in primordial oceans
 First known fossils 3.5 bya
 First cells prokaryotic
 Bacteria and Archaea are similar but different
 All life forms prokaryotic during Archaeon Eon
 Hardly any free oxygen so organism were anaerobic
 First cells were heterotrophs
 Autotrophs evolved as supply of organic molecules dwindled
Stromatolites
 Autotrophic cyanobacteria were preserved when heterotrophic ancestors were not
 Form stromatolites- layered structure of calcium carbonate
 Cyanobacteria produce oxygen as a waste product of photosynthesis
 Spelled doom for many prokaryotic groups that were anaerobic
 Allowed the evolution of aerobic species
The Origin of Eukaryotic Cells During the Proterozoic Eon Involved a Union Between Bacterial and
Archaeal Cells
 Origin of first eukaryotic cell matter of debate
 In modern eukaryotes, DNA found in nucleus, mitochondria and chloroplasts
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 Examine properties of this DNA and modern prokaryotes
 Nuclear genome – both bacteria and archaea contributed substantially
 Symbiotic relationship – 2 species live in direct contact
 Endosymbitoic – one organism lived inside another
Data supports this origin
Proterzoic Eon
 Multicellular eukaryotes arise 1.5 bya
 2 possible origins
 Individuals form a colony
 Single cell divides and stays stuck together
 Volvocine green algae display variations in the degree of multicellularity
 Multicellular animals emerge toward the end of the eon
 First animals invertebrates
 Bilateral symmetry facilitates locomotion
Phanerzoic Eon
 Proliferation of multicellular eukaryotic life extensive during Phanerzoic Eon (543 mya to today)
 Paleozoic Era
 Mesozoic Era
 Cenozoic Era
Phanerzoic Eon, Paleozoic Era
 543-248 mya
 Cambrian period
 Ordovician period
 Silurian period
 Devonian period
 Carboniferous period
 Permian period
Phanerzoic Eon, Paleozoic Era, Cambrian Period
 543-490 mya
 Warm and wet with no ice at poles
 Cambrian explosion – abrupt increase in diversity of animal species
 Cause unknown – shell evolution, atmospheric oxygen?
 All existing major types of marine invertebrates plus many other that no longer exist
 Although new species have arisen since, no major reorganizations of body plans
 First vertebrates 520 mya
Phanerzoic Eon, Paleozoic Era, Ordovician Period
 490-443 mya
 Warm temperatures and atmosphere very moist
 Diverse group of marine invertebrates including trilobites and brachiopods
 Primitive land plants and arthropods first invade land
 Toward end, abrupt climate change (large glaciers) resulting in mass extinction
 Over 60% of existing marine invertebrates became extinct
Phanerzoic Eon, Paleozoic Era, Silurian Period
 443-417 mya
 Relatively stable climate
 Glaciers largely melted
 No new major invertebrates
 Significant new vertebrates and plants
 Many new fish
 Coral reefs appeared
 Large colonization by terrestrial plants and animals
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 Had
to evolve adaptations to drying out
 Spiders and centipedes
 Earliest vascular plants
Phanerzoic Eon, Paleozoic Era, Devonian Period
 417-354 mya
 Generally dry across north but southern hemisphere mostly covered by cool, temperate oceans
 Major increase in number of terrestrial species
 Ferns, horsetails and seed plants (gymnosperms) emerge
 Insects emerge
 Tetrapods – amphibians emerge
 Invertebrates flourish in the oceans
 Age of Fishes
 Near end, prolonged series of extinctions eliminate many marine species
Phanerzoic Eon, Paleozoic Era, Carboniferous Period
 354-290 mya
 Rich coal deposits formed
 Cooler, land covered by forested swamps
 Plants and animals further diversified
 Very large plants and trees prevalent
 First flying insects
 Amphibians prevalent
 Amniotic egg emerges - reptiles
Phanerzoic Eon, Paleozoic Era, Permian Period
 290-248 mya
 Continental drift formed supercontinent Pangaea
 Interior regions dry with seasonal fluctuations
 Forest shift to gymnosperms
 Amphibians prevalent but reptile became dominant
 First mammal-like reptiles appeared
 At the end, largest known mass extinction event
 90-95% of all marine species and large proportion of terrestrial species eliminated
 Glaciations or volcanic eruptions blamed
Phanerzoic Eon, Mesozoic Era
 Permian extinction marks boundary between Paleozoic and Mesozoic eras
 Age of Dinosaurs
 Consistently hot climate, dry terrestrial environments, little if any ice at poles
Phanerzoic Eon, Mesozoic Era, Triassic Period
 248-206 mya
 Reptiles plentiful
 First dinosaurs
 First true mammals
 Gymnosperms dominant land plant
 Volcanic eruptions led to global warming and mass extinctions near the end
Phanerzoic Eon, Mesozoic Era, Jurassic Period
 206-144 mya
 Gymnosperms continued to be dominant
 Dinosaurs dominant land animal
 Some attained enormous size
 First known bird
 Mammals present but not prevalent
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Phanerzoic Eon, Mesozoic Era, Cretaceous Period
 144-65 mya
 Dinosaurs still dominant on land
 Earliest flowering plants, angiosperms
 Another mass extinction at the end of the period
 Dinosaurs and many other species died out
 Large meteorite/asteroid or volcanic eruptions blamed
Phanerzoic Eon, Cenozoic Era
 Spans most recent 65 million years
 Tropical conditions replaced by a colder, drier climate
 Amazing diversification of birds, fish, insects, and flowering plants
Phanerzoic Eon, Cenozoic Era, Tertiary Period
 65-1.8 mya
 Mammals that survived expanded rapidly
 Birds and terrestrial insects diversified
 Angiosperms become the dominant land plant
 Fish diversified
 Sharks become abundant
 Whales appeared
 Hominids appeared about 7 mya
Phanerzoic Eon, Cenozoic Era, Quaternary Period
 1.8 mya to present
 Periodic ice ages cover much of Europe and North America
 Widespread extinction of many species
 Certain hominids become more human-like
 Homo sapiens appears 130,000 years ago
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