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


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

the origins of life on earth(or, a History of
our planet in 90 minutes or less)
  • biology 1

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

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

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)

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

Physical conditions of early Earth - Coincidence
  • 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
  • High energy bombardment from sun
  • ??promotes generation of organics

Spontaneous origins of life - 4 steps
  • Abiotic synthesis and accumulation of organic
  • Polymerization
  • Aggregation of polymers into nonliving structures
  • Oparins Bubble theory
  • Origin of heredity

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
  • Abiotically produced proteins (proteinoids)
    self-assemble into Protobionts (selectively
    permeable membrane)

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

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)

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

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

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

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

Monera the Pioneers of Life on Earth
  • The most successful group of organisms on the
  • 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

The phylogeny of Prokaryotes
Kingdom Protista
Kingdom Plantae
Kingdom Animalia (Invertebrata)
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)

Kingdom Animalia (Vertebrata)
The Evolution of Man
Mankind stood up first and got smart later
Stephen Jay Gould
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

  • Earliest hominids diverged 5 mya (Ardipithecus)
  • Distinguished by bipedal stance
  • Most fossil specimens of early hominids are
  • 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

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
  • Systematics provide little information on
    relationships between various species of
  • e.g. Lucy, 1974 A. afarensis

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

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

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

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

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
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