Ch 12 History of Life on Earth

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Ch 12 History of Life on Earth
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• The Earth formed about 4.5 billion years ago
• The Earth was a fiery ball of molten rock that
  cooled, forming an outer crust

• Water vapor condensed and formed the oceans
• Nonliving matter reacted chemically to create
  organic molecules, the building blocks of living
  things

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How do we know this?

• Radiometric dating
• Measures the age of rocks by the amount of
  radioactive isotopes in a rock
• Allows a scientist to determine how long a rock
  has existed on Earth
• Rocks dating back to about 4 bya

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How did Life Originate?-Chemical Evolution
First(formation of organic compounds
nucleotides -gt nucleic acids)-Biological
Evolution Second (living things)
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Miller-Urey Experiment

• conducted in 1953 by Stanley Miller with Harold
  Urey
• the first experiment about the evolution of
  pre-biotic chemicals and the origin of life on
  Earth
• mixture of methane, ammonia, hydrogen, and water
  vapor introduced into a 5-liter flask (simulate
  the Earth's primitive atmosphere)
• energized by an electrical discharge apparatus to
  represent lightning
• products were allowed to condense and collect in
  a lower flask which modeled a body of water on
  the Earth's surface

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Miller-Urey Experiment

• heat supplied to this flask recycled the water
  vapor just as water evaporates from lakes and
  seas, before moving into the atmosphere and
  condensing again as rain
• after a day of continuous operation
• a thin layer of hydrocarbons on the surface of
  the water
• after about a week of operation
• a dark brown scum had collected in the lower
  flask and was found to contain several types of
  amino acids, including glycine and alanine,
  together with sugars, tars, and various other
  unidentified organic chemicals

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The Bubble Model

• 1986 Geophysicist Louis Lerman
• The key processes that formed the chemicals
  needed for life took place within bubbles in the
  ocean

• Gases trapped in underwater bubbles from undersea
  volcanoes
• Gases underwent chemical reactions and formed
  simple organic molecules
• Gases released into air
• Gases underwent further reactions
• Simple and complex compounds fell into the oceans

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Evolution of First Life

• Formation of the earliest precursors of life
• must have self-organized
• acquired the capabilities needed to survive and
  reproduce
• Biomolecules of life became enclosed within a
  lipid membrane
• Essential protocellular functions
• acquisition of energy from the environment
• use of energy to synthesize molecules
  metabolism
• information transfer to succeeding generations
  genetics

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EVOLUTIONdescent with modification from a common
ancestor as a result of natural selection acting
on genetic variation, both in the short run, as
gene frequency changes from generation to
generation (microevolution), and over many
generations, leading to new species
(macroevolution)
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What Types of Life exist on the Earth?
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Types of Organisms

• Prokaryotic Kingdom single-celled organisms,
  cell membrane, no organelles, no nucleus
• Microscopic fossils of prokaryotes come from rock
  that is 2.5 billion years old

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Prokaryotes

• Eubacteria (bacteria)
• E. coli (used in our pGLO lab)
• Contain peptidoglycan in their cell walls

• Archaebacteria
• Lack peptidoglycan in their cell walls
• Have unique lipids in their cell membranes
• More closely related to eukaryotes than to
  bacteria

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Endosymbiotic Theory

1. Size and structure are similar to eubacteria
2. Similar genetic material-circular DNA, genes are
   different from those found in the nucleus of the
   host cell
3. Similar size and structure of ribosomes
4. Fission reproduction

• Mitochondria and chloroplasts descended from
  bacteria

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Endosymbiotic TheoryEndo-inside,
symbiosis-living together
Chloroplast
Plants and plantlike protists
Aerobic bacteria
Ancient Prokaryotes
Photosynthetic bacteria
Nuclear envelope evolving
Mitochondrion
Primitive Photosynthetic Eukaryote
Animals, fungi, and non-plantlike protists
Primitive Aerobic Eukaryote
Ancient Anaerobic Prokaryote
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Types of Organisms

• Eukaryotes appeared about 1.5 billion years ago.
• Eukaryotic Kingdoms all organisms consisting of
  cells which contain membrane-bound nuclei and
  organelles
• Protista - mostly one-celled organisms, algae
  have characteristics of all three other Eukaryote
  Kingdoms
• Fungi - organisms which decompose dead organisms
• Plantae - organisms which use photosynthesis to
  make their own food
• Annuals complete life cycle in one season
• Perennials live for more than one season
• Animalia - organisms which must get organic
  compounds from food they eat - most are able to
  move
• Invertebrates no backbone, Insects
• Vertebrates Fish, Amphibians, Reptiles, Birds
  and Mammals

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Advantages

• Unicellularity
• Asexual reproduction results in many offspring
  quickly
• Small, simple

• Multicellularity
• Different cells perform specialized functions
• Unique offspring from sexual reproduction
• Oldest known fossils of multicellular organisms
  found in 700 million year old rocks

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Mass extinction

• Extinction-death of all members of a species
• Mass extinction-episode during which large
  numbers of species become extinct

• 5 major mass extinctions
• 440 million years ago-end of Ordovician period
• 360 mya
• 245 mya-Permian period
• 200 mya
• 65 mya (dinosaurs extinct)
• Causes-evidence indicates worldwide geological
  and weather changes were factors

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Life on land

• Life formed in the seas
• Protection from UV radiation from the sun
• Photosynthetic cyanobacteria in water created
  oxygen which built up in atmosphere

• Ozone molecules (O3) formed in the upper
  atmosphere which blocks UV radiation

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• Plants and fungi were first multicellular
  organisms to move to land
• Arthropods were first animals to move to land
  (insects, crustaceans)

• First vertebrates were small, jawless fish in
  oceans 530 mya
• Amphibians were first vertebrates to inhabit land
  370 mya
• Reptiles
• Mammals and birds

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