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The Origin of Life

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Chapter 26 The Origin of Life Origin of Life Earth formed 4.5 billion years ago and life began a few hundred million years later Organisms were only microscopic and ... – PowerPoint PPT presentation

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Title: The Origin of Life


1
Chapter 26
  • The Origin of Life

2
Origin of Life
  • Earth formed 4.5 billion years ago and life began
    a few hundred million years later
  • Organisms were only microscopic and unicellular
    for the first ¾ of evolutionary history
  • Stromatolites are rocks made of banded domes of
    sediment in which are formed the most ancient
    forms of life prokaryotes dating back as far as
    3.5 billion years

3
Major Episodes in the History of Life
  • the production of oxygen by early photosynthetic
    prokaryotes created an aerobic atmosphere
    aerobic life evolved
  • oldest eukaryotic fossils are about 1.7 billion
    years old
  • eukaryotic cells probably evolved from a
    symbiotic community of prokaryotes
  • plants, fungi, and animals came from unicellular
    eukaryotes during the Precambrian period
  • plants evolved from green algae

4
Major Episodes in the History of Life
  • fungi and animals evolved from heterotrophic
    unicellular organisms
  • the oldest animal fossils were from about 700
    million years ago
  • life on Earth was aquatic for 90 of its
    existence
  • when plants colonized land, they changed the
    landscape and created more opportunities for life
    on land

5
Prebiotic Chemical Evolution
  • the first organisms were products of a chemical
    evolution in four stages
  • abiotic synthesis and accumulation of small
    organic molecules
  • the joining of these monomers into polymers
  • the aggregation of abiotically produced molecules
    into droplets called protobionts
  • the origin of heredity

6
Abiotic Synthesis of Organic Monomers
  • The conditions of early Earth favored the
    chemical reactions that synthesized organic
    compounds from inorganic materials.
  • Primitive atmosphere consisted of reducing
    (electron adding) gases, instead of oxygen-rich
    atmosphere, enhancing the creation of complex
    molecules.
  • Lightning and UV radiation from the sun probably
    provided the energy needed to catalyze the
    reactions.

7
Abiotic Synthesis of Organic Monomers
  • Stanley Miller and Harold Urey recreated early
    Earth conditions in a lab and have synthesized
    several organic compounds including all 20 amino
    acids, lipids, several sugars, and the bases
    found in DNA and RNA

8
Production of Organic Polymers
  • Dilute solutions of organic monomers dripped onto
    hot sand, clay, or rocks causes polymerization.
  • Clay was especially important because monomers
    bind to charged sites on the clay particles
  • Pyrite, also called fools good, could have been
    the substratum or organic synthesis because it
    has a charged surface and it yields electrons
    that support bonding between organic materials

9
Protobionts
  • Living cells may have been preceded by
    protobionts, aggregates of abiotically produced
    molecules.
  • These protobiont droplets show some
    characteristics of life metabolism and
    excitability.
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