the origins of life on earth (or, a History of our planet in 90 minutes or less)

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the origins of life on earth(or, a History of
our planet in 90 minutes or less)

• biology 1

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• How old is this planet anyway?
• Theories of Origin
• Geological and Biological timescales
• Phylogeny

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How old is this planet anyway?

• The Universe is probably 13 billion years old
  (Big Bang Theory/Doppler Shift)
• Earth is 4.5 billion years old (begins with
  cooling of crust/solidification)
• Earliest records of life 3.5 billion years ago
• First humans (Australopithecus), 0.005 billion
  years ago
• Discovery of Australopithecus fossils ,
  0.0000000002 billion years ago

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The Fragility of Life - Coincidence 1

• Life can only exist within temperatures
  corresponding to the boiling and freezing point
  of water
• This range is a fraction of the range between
  absolute zero (-273C) and the temperature of the
  sun (106C)

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How did life evolve?

• Three theories
• Creationism
• Extraterrestrial origin (Panspermia)
• Spontaneous Origin (Coincidence 2)
• Black smokers?

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Physical conditions of early Earth - Coincidence
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• Temperatures in correct range (in general, water
  in fluid state, carbon compounds non-brittle)
• Size of planet retains an atmosphere
• Early atmosphere lacked oxygen, therefore highly
  reductive
• High energy bombardment from sun
• ??promotes generation of organics

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Spontaneous origins of life - 4 steps

• Abiotic synthesis and accumulation of organic
  compounds
• Polymerization
• Aggregation of polymers into nonliving structures
  (Protobionts)
• Oparins Bubble theory
• Origin of heredity

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Experimental evidence of Spontaneous Origin

• Theories of Oparin and Haldanetested by Miller
  and Ureydemonstrate formation of organics under
  conditions typical of early Earth
• Polymerization can occur with appropriate
  substrate
• Abiotically produced proteins (proteinoids)
  self-assemble into Protobionts (selectively
  permeable membrane)

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The final key - Heredity

• First passage of genetic information probably
  occurred through short strands of RNA (also
  autocatalyst, e.g ribozymes)
• Mutations cause variation
• Natural selection of molecular combinations
• Origin of DNA

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Biological time scales

• Biological timescales by necessity follow
  geological timescales
• Often, geological events marked by key biological
  events (mass extinctions/diversifications)
• First fossil record of life 3.5 billion years ago
  (prokaryote), in the Precambrian
• Earliest eukaryote 1.5 billion years ago
  (endosymbiotic theory)

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Earth - The Early Years

• Late Precambrian saw the first eukaryotic
  multicellular life
• Boundary between Precambrian and Cambrian (580
  mya) marked by a rapid adaptive
  radiation/diversification of marine life
  (Cambrian explosion)
• By the middle of the Cambrian, all of the animal
  phyla existing today had evolved

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The drive behind Macro-Evolution

• Biological forces natural selection working in
  general, but particularly effectively on genes
  controlling allometric growth (differential
  growth of parts of body
• Physical forces
• Plate tectonics, leading to formation and
  splitting of supercontinents

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The study of evolutionary history Phylogeny

• Modern Darwinian synthesis suggests adaptive
  radiation from a common ancestor
• Concept of phylogeny supported through studies of
  homology
• Traditional classification systems (Linnaeus) are
  monophyletic, based on homology ? parallel or
  divergent evolution
• Some groupings are polyphyletic, with analogous
  structure ? convergent evolution

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The Kingdom System

• Scientists follow various taxonomic systems
  Campbell uses the 5 kingdom classification scheme
• Monera
• Protista
• Plantae
• Fungi
• Animalia

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Monera the Pioneers of Life on Earth

• The most successful group of organisms on the
  planet
• 3.5 billion year history
• Although only 4000 species known, the number of
  extant species is thought to be 4,000 4 x106
• Found in all ecological niches, including some
  where other forms of life cannot exist

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The phylogeny of Prokaryotes
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Kingdom Protista
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Kingdom Plantae
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Kingdom Animalia (Invertebrata)
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Phylogeny recounts the natural selection of
species (Earth the Middle Years)

• First major extinction at end of the Paleozoic
  era (the Permian Extinction), probably caused by
  collision of tectonic plates to form the
  supercontinent, Pangaea
• Pangaea marks the birth of a new era, the
  Mesozoic (Triassic, Jurassic, Cretaceous)
• Mesozoic ends with second mass extinctionthe
  Cretaceous Extinction (impact hypothesis)

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Kingdom Animalia (Vertebrata)
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The Evolution of Man
Mankind stood up first and got smart later
Stephen Jay Gould
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Placental mammals included the Hominoids...

• Apes include Gibbons (Hylobates), Orangutan
  (Pongo), Gorillas (Gorilla) and Chipanzees (Pan)
• Most are ground dwelling and lack tails
• Some are closely related to Homo sapiens in terms
  of nuclear DNA
• Gorilla (97.7) diverged 8 mya
• Pan (98.4) diverged 6 mya
• Hominids include Ardipithecus, Australopithecus,
  and Homo

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Hominids

• Earliest hominids diverged 5 mya (Ardipithecus)
• Distinguished by bipedal stance
• Most fossil specimens of early hominids are
  Australopithecus
• Appearance in fossil record coincident with
  cooling of Africa to convert rain forests to
  savannah plain, resulting in a rapid adaptive
  radiation of at least 6 species

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Australopithecus - forerunner or evolutionary
dead end?

• Apelike - large face, small skull/brain size (400
  cm3). Bipedal, developed grip
• Well developed teeth, indicating movement to
  tougher foods that required more physical
  digestion
• Systematics provide little information on
  relationships between various species of
  Australopithecus
• e.g. Lucy, 1974 A. afarensis

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The first humans, early Homo

• Genus Homo distinguished by larger brain size
  700 cm3, evolving 2 mya
• First association with tools Homo habilis,
  handy man. Short, long arms - intiially thought
  to be a species of Australopithecus
• Mystery species H. rudolfensis had larger brain,
  appeared to co-exist with H. habilis

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Late Homo

• Homo erectus, the first true human?
• Very large brain 1000cm3
• Probably not the direct ancestor of modern man
• May have had speech ability
• Cave-dwelling hunters, used fire, clothed in
  animal skins
• Nomadic, responsible for rapid spreading into
  Asia and Europe by 0.5 mya

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The final phase...

• Homo neanderthalensis orginated in Africa, but
  rapidly spread to other continents. Very common
  100,000 years ago, but not the ancestor of modern
  man. Disappeared 35,000 ya
• Examination of burial grounds suggests social
  ritualism - the first evidence of abstract thought

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Homo sapiens

• probably evolved from H. heidelbergensis, a close
  relative of H. neaderthalensis
• Oldest known H. sapiens fossil is 130,000 years
  old, cranial capacity of 1500 cm3
• Controversy over origin
• Monogenesis model
• Multiregional model

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And now...

• Currently in the Recent epoch of the Quarternary
  period of the Cenozoic era
• History may tell of a third mass extinction?
• Radically changing planet will continue to apply
  selective pressure to species