Early Earth and the Origin of Life

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Early Earth and the Origin of Life

• Chapter 26

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Evolution of Life on Earth

• Life on earth originated between 3.5 and 4.0
  billion years ago.
• Earth formed about 4.5 billion years ago.
• The oldest fossils of prokaryotes are 3.6 billion
  years old.

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First 3/4 of evolutionary history- organisms were
microscopic based on molecular clocks.
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Domination of Prokaryotes

• Prokaryotes dominated evolutionary history from
  3.5 to 2.0 bya.
• The two domains of prokaryotes, Bacteria and
  Archaea, diversified as a variety of metabolic
  types living near hydrothermal vents and in
  shallow water communities that left fossils
  called stomalites.

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Clock Analogy for Key Events in Evolutionary
History
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Introduction of Oxygen

• Oxygen began accumulating in the atmosphere about
  2.5 bya.
• Oxygenic photosynthesis evolved in cyanobacteria.
• As O2 accumulated in the atmosphere, the reactive
  molecule posed an environmental challenge for
  life.
• Some species survived in habitats that remained
  anaerobic.
• Among other survivors, a diversity of adaptations
  to the changing atmosphere evolved (cellular
  respiration).

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Evolution of Eukaryotic Life

• Eukaryotic life began by 2.1 bya.
• The oldest fossils of eukaryotes date back 2.1
  billion years.
• The eukaryotic cell evolved from a prokaryotic
  ancestor that hosted smaller internal
  prokaryotes.
• Endosymbiotic Theory

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Evolution of Multicellular Life

• Multicellular eukaryotes evolved by 1.2 bya.
• There are fossils of multicellular algae dating
  back 1.2 billion years.
• The oldest fossils of animals are about 600
  million years old.

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The Cambrian Explosion

• Animal diversity exploded during the early
  Cambrian period.
• Most phyla of animals make their first fossil
  appearance during a relatively brief span from
  about 540-520 million years ago.
• Plants, fungi, and animals colonized land about
  500 million years ago.
• A symbiotic relationship of plants with fungi
  contributed to the move onto land.
• Herbivorous animals and their predators followed.

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Figure 26.8 The Cambrian radiation of animals
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The Origin of Life

• The first cells may have originated by chemical
  evolution on a young Earth.
• Though life today arises by biogenesis, the very
  first cells may have been products of a prebiotic
  chemistry.
• This idea of life emerging from inanimate
  material is called spontaneous generation.

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The Origin of Life

• Although there is NO evidence that spontaneous
  generation occurs today, conditions on the early
  Earth were very different.
• Relatively little atmospheric oxygen to tear
  apart complex molecules
• Energy sources such as lightening, volcanic
  activity, and UV light were more intense

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Four-Stage Hypothesis for the Origin of Life

• According to one hypothetical scenario, the first
  organisms were products of chemical evolution in
  four stages
• Abiotic synthesis of small organic molecules,
  such as amino acids and nucleotides.
• Joining of small molecules (monomers) into
  polymers, including proteins and nucleic acids.
• Origin of self-replicating molecules that
  eventually made inheritance possible
• Packaging of these molecules into protobionts
  droplets with membranes that maintained an
  internal chemistry different from the
  surroundings.

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BIOCHEMICAL EVOLUTION

• 1) The Earth and its atmosphere formed
• Gasses present when the atmosphere was first
  formed included CO, CO2, H2, N2, H2O, S, HCl, HCN
  (hydrogen cyanide), but little or no O2.
• A.I. Oparin and J.B.S. Haldane independently
  theorized that simple molecules were able to form
  only because oxygen was absent. WHAM prevalent in
  atmosphere (water, hydrogen, ammonia, methane)
• As a very reactive molecule, oxygen, had it been
  present, would have prevented the formation of
  organic molecules by supplanting most reactants
  in chemical reactions.

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BIOCHEMICAL EVOLUTION

• 2) The primordial seas formed.
• As the earth cooled, gases condensed to produce
  primordial seas consisting of water and minerals
  (beginning of hydrologic cycle).
• 3) Complex molecules were synthesized.
• Chemicals present in the ancient seas
• Acetic acid, formaldehyde, and amino acids. These
  kinds of molecules would later serve as monomers,
  or unit building blocks, for the synthesis of
  polymers.

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How were the first organic molecules created?

• Energy catalyzed the formation of organic
  molecules from inorganic molecules. An organic
  soup formed.
• NO ENZYMES WERE NEEDED.
• Energy was provided mostly by ultraviolet light
  (UV), but also lightening, radioactivity, and
  heat- hydrothermal vents (hot volcanic outlets in
  the deep-sea floor).

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Figure 26.10x Lightning
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Abiotic Synthesis is Testable

• Laboratory experiments performed under conditions
  simulating those of the primitive Earth have
  produced diverse organic molecules from inorganic
  precursors.

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Figure 26.9 Pasteur and biogenesis of
microorganisms (Layer 3)
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Stanley Miller and Harold Urey

• Using an airtight apparatus, CH4 (methane), NH3
  (ammonia), H2O, H2 and a high voltage discharge,
  they found that after one week the water
  contained various organic molecules including
  amino acids.
• (WHAM! Water, hydrogen, ammonia, methane)
• The amino acids synthesized are the building
  blocks of proteins for organisms.
• Proteinoids are abiotically produced
  polypeptides. They can be experimentally produced
  by allowing amino acids to dehydrate on hot, dry
  substrates.
• Adenine and other nucleotides are the building
  blocks of RNA (also- Adenine for ATP).

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Figure 26.10 The Miller-Urey experimenthttp//bc
s.whfreeman.com/thelifewire/content/chp03/0301s.sw
f
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RNA First Genetic Material?

• The RNA world preceded todays DNA world.
• RNA may have been the first genetic material.
• The first genes may have been abiotically
  produced RNA, whose base sequences served as
  templates for both alignment of amino acids in
  polypeptide synthesis and alignment of
  complementary nucleotide bases in a primitive
  form of self-replication.

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Figure 26.11 Abiotic replication of RNA
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The First Heterotrophs

• Prokaryotic Heterotrophs feeding on organic
  molecules in the seas began to develop
  metabolism.
• The first form of metabolism (fermentation) using
  glycolysis most likely arose because the
  atmosphere lacked free oxygen anaerobic

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Autotrophic Evolution

• The first autotrophs were probably nonoxygenic
  photosynthesizers.
• They did not split water and liberate oxygen
  (cyclic only)
• The first organisms to use noncyclic
  photosynthesis or oxygenic photosynthesis
  (water-splitting enzyme) were probably
  cyanobacteria (blue-green algae)

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Creating the Ozone

• A byproduct of oxygenic photosynthesis was oxygen
  and as it accumulated in the atmosphere (2.7-2.2
  billion years ago),
• First dissolved into the surrounding water until
  the seas and lakes became saturated with oxygen.
• Additional oxygen would then react with dissolved
  iron and precipitate as iron oxide.
• Then additional oxygen finally began to gas out
  of the seas etc. and accumulate in the
  atmosphere.
• The ozone layer was created.
• As the ozone absorbed UV rays, the major source
  of energy for abiotic synthesis of organic
  molecules and primitive cells was terminated.

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Effect of Oxygen on Earth

• The oxygen had a tremendous impact on Earth
• Corrosive O2 attacks chemical bonds, doomed many
  prokaryotes.
• Some survived in anaerobic environments (obligate
  anaerobe survivors)
• Others adapted- cellular respiration.

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The First Eukaryoteshttp//highered.mcgraw-hill.c
om/sites/9834092339/student_view0/chapter4/animati
on_-_endosymbiosis.html

• Evolution of Eukaryotic organelles from
  prokaryotes occurred about 2.1 billion years ago.
• Mitochondria and Chloroplasts are descendents of
  endosymbionts- symbiotic cells living within
  larger host cells.
• Many eukaryotes may have evolved from prokaryotes
  enjoying a mutually beneficial relationship
  (symbiosis).
• Endosymbiotic theory- Margulis.

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Endosymbiosis Theory (Lynn Margulis, 1970s)
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Evidence for Endosymbiosis

1. Mitochondria and chloroplasts resemble bacteria
   and cyanobacteria with respect to their DNA, RNA,
   and protein synthesis machinery.
2. Mitochondria and chloroplasts reproduce
   independently of their eukaryotic host cell.
3. Ribosomes of mitochondria and chloroplasts
   reproduce independently of their eukaryotic host
   cell.
4. The thylakoid membranes of chloroplasts resemble
   the photosynthetic membranes of cyanobacteria.

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Timeline of Classification

• 1. 384 322 B.C. Aristotle
• 2 Kingdom Broad Classification Plants or
  Animals
• 2. 1735 - Carl Linnaeus
• 2 Kingdom Multi-Divisional Classification
• (Kingdom, Phylum, Class, Order, Family Genus,
  Species)
• 3. Evolutionary Classification (After Darwin)
• Group By lines of Evolutionary Descent
• 4. Five Kingdom System 1950s
• (Whittaker) 1950s Plantae, Fungi, Animalia,
  Protista, Monera
• 6. Three Domain System late 1990s
• late 1990s Bacteria, Archaea, Eukarya

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Linnaeus System Evolves from TWO Kingdoms to FIVE

• As we learned more about different kinds of life,
  there needed to be more Kingdoms
• 1800s Added Kingdom Protista
• Amoeba, Slime Molds
• 1950s Added Fungi and Monera
• Fungi distinguished from Plants
• Prokaryotes (no nucleus) bacteria given category
• 1970s Split Kingdom Monera into 2 separate
  Kingdoms
• Eubacteria bacteria with peptidoglycan
• Archaebacteria bacteria without peptidoglycan

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The Five-Kingdom System

• Reflected increased knowledge of lifes diversity
• Kingdom is highest most inclusive taxonomic
  category
• Five Kingdoms include
• Monera
• Protista
• Plantae
• Fungi
• Animalia
• Recognized 2 types of cells prokaryotes
  eukaryotes

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The Five-Kingdom System

• Described classification as
• Plantae, Fungi, Animalia, Protista, Monera
• recognizes only 2 types of cells prokaryotic and
  eukaryotic
• sets all prokaryotes apart from eukaryotes
• prokaryotes are in their own kingdom (Monera)
• distinguished 3 kingdoms of eukaryotes based on
  mode of nutrition
• protista were all eukaryotes that did not fit the
  definition of plants, fungi, or animals

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Figure 26.15 Whittakers five-kingdom system
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Figure 26.16 Our changing view of biological
diversity
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The Three-Domain Systemhttp//bcs.whfreeman.com/t
helifewire/content/chp27/27020.html

• Molecular analyses have given rise to the most
  current classification system the Three Domain
  System
• Domain is larger than kingdom (superkingdoms)
• The 3 Domain System is the most recent
  classification system and includes
• Bacteria
• Archaea
• Eukarya

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The Three Domain System

• Describes classification as
• Not all prokaryotes are closely related (not
  monophyletic)
• Prokaryotes split early in the history of living
  things (not all in one lineage)
• Archaea are more closely related to Eukarya than
  to Bacteria
• Eukarya are not directly related to Eubacteria
• There was a common ancestor for all extant
  organisms (monophyletic)
• Eukaryotes are more closely related to each other
  (than prokaryotes are to each other)

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Section 18-3
Classification of Living Things
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