The Origin and Evolution of Life

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The Origin and Evolution of Life

• Chapter 20

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• The earth is more than 4.5 billion years old
• The PreCambrian era spans 4 bllion years,
  scontaining the Archean and Proterozoic eons

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The Paleozoic, Mesozoic and Cenozoic eras are in
the Phenerozoic eon which spans the last 545
million years.
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The Origin and Evolution of Life
Fig. 21.2, p. 336
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X
Y
Fig. 21.1, p. 334
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The Big Bang

• 12-15 billion years ago all matter was compressed
  into a space the size of our sun
• Sudden instantaneous distribution of matter and
  energy throughout the known universe

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Archeon Eon and Earlier

• 4,600 mya Origin of Earth
• 4,600 - 3,800 mya
• Formation of Earths crust, atmosphere
• Chemical and molecular evolution
• First cells (anaerobic bacteria)

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Earth Forms

• About 4.6 and 4.5 billion years ago
• Minerals and ice orbiting the sun started
  clumping together
• Heavy metals moved to Earths interior, lighter
  ones floated to surface
• Produced outer crust and inner mantle

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Earth Is Just Right for Life

• Smaller in diameter, gravity would not be great
  enough to hold onto atmosphere
• Closer to sun, water would have evaporated
• Farther from sun, water would have been locked up
  as ice

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Early Earth

• Primitive atmosphere
• H2
• N2
• CO
• CO2
• Probably no O2

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First Atmosphere

• Hydrogen gas
• Nitrogen
• Carbon monoxide
• Carbon dioxide
• No gaseous oxygen

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Origin of Organic Compounds

• Amino acids, other organic compounds can form
  spontaneously under conditions like those on
  early Earth
• Clay may have served as template for complex
  compounds
• Compounds may have formed near hydrothermal vents

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Synthesis of Organic Compounds

• Stanley Millers experiment
• Methane, hydrogen, ammonia and water in a
  reaction chamber
• Simulated lightning
• Amino acids and small organic compounds formed

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Fig. 21.3, p. 337
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Origin of an Energy Producing Molecule Porphyrin
Ring Structure
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Chemical Evolution
chlorophyll a

• Spontaneous formation of porphyrin rings from
  formaldehyde
• Components of chlorophylls and cytochromes

formaldehyde
porphyrin ring system
Figure 20.4  Page 720
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RNA World

• DNA is genetic material now
• DNA-to-RNA-to-protein system is complicated
• RNA may have been first genetic material
• RNA can assemble spontaneously
• How switch from RNA to DNA might have occurred is
  not known

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Proto-Cells

• Microscopic spheres of proteins or lipids can
  self assemble
• Tiny sacs like cell membranes can form under
  laboratory conditions that simulate conditions in
  evaporating tidepools
• Nanobes may resemble proto-cells

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From a more humanistic point of view,
individuality entered the world when the first
membrane fragment wrapped itself into a closed
shell and separated the interior components from
the rest of the universe. Harold
MorowitzMayonnaise and the Origin of Life (1985)
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Making Mayonnaise
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• Mix vegetable oil, vinegar, and egg yolk.
• How do they form a nice smooth mixture since
  everyone knows that oil and water "don't mix".?
• Egg yolk which contains the phospholipid lecithin
  which is amphipathic (it interacts simultaneously
  with polar water and nonpolar lipids) because
  pspholipids have a both a hydrophilic side and
  hydrophobic side.
• The hydrophobic portion of the molecule
  essentially forms a shell around the vegetable
  oil while the hydrophilic side points outward
  toward the vinegar mixture which emulsifies the
  oil and results in a smooth mayo.

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abiotic protein and lipid vesicles
Fig. 21.5, p. 339
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Possible Sequence
membrane-bound proto-cells
self-replicating system enclosed in a selectively
permeable, protective lipid sphere
Figure 20.5  Page 331
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Proterozoic Eon

• Origin of photosynthetic Eubacteria
• Noncyclic pathway first
• Cyclic pathway next
• Oxygen accumulates in atmosphere
• Origin of aerobic respiration

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The First Cells

• Originated in Archeon Eon
• Were prokaryotic heterotrophs
• Secured energy through anaerobic pathways
• No oxygen present
• Relied on glycolysis and fermentation

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Origin of Prokaryotic and Eukaryotic Cells
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History of Life
ARCHAEBACTERIAL LINEAGE
ANCESTORS OF EUKARYOTES
Noncyclic pathway of photosynthesis
Cyclic pathway of photosynthesis
ORIGIN OF PROKARYOTES
Aerobic respiration
Figure 20.6  Page 332
3.8 bya
3.2 bya
2.5 bya
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History of Life
ARCHAEBACTERIA
Extreme halophiles
Methanogens
Extreme thermophiles
ORIGINS OF ANIMALS
EUKARYOTES
ORIGINS OF EUKARYOTES
Animals
Heterotrophic protistans
ORIGINS OF FUNGI
Fungi
Photosynthetic protistans
ORIGINS OF MITOCHONDRIA
Plants
ORIGINS OF PLANTS
ORIGINS OF CHLOROPLASTS
EUBACTERIA

Photosynthetic oxygen producers
Other photosynthetic bacteria

Chemotrophs, heterotrophs
Figure 20.6  Page 332
1.2 bya
900 mya
435 mya
present
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Where Did Organelles Come From ?

• Membranous enclosures
• Nucleus
• ER
• Endosymbiosis
• Mitochondria
• Chloroplasts
• Both have self-replicating DNA, divide
  independently of cell

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Advantages of Organelles

• Nuclear envelope may have helped to protect genes
  from competition with foreign DNA
• ER channels may have protected vital proteins

DNA
infolding of plasma membrane
Figure 20.10  Page 335
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Theory of Endosymbiosis

• Lynn Margulis
• Mitochondria and chloroplasts are the descendents
  of free-living prokaryotic organisms
• Prokaryotes were engulfed by early eukaryotes and
  became permanent internal symbionts

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Endosymbiosis
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Cyanophora paradoxa
cyanobacterium-like structure
mitochondrion
nucleus
The chloroplasts of Cyanophora, a member of the
Kingdom Protista resemble spherical
photosynthetic bacteria
Fig. 21.12, p. 343
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start of long flagellum
chloroplast
mitochondrion
nucleus
5 µm
the photosynthetic protist Euglena
Fig. 21.10, p. 342
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A strand of 3.5 billion year old prokaryotic
cells from Australia.
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1 1.4 billion year old prokaryotes
Fig. 21.9, p. 342
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Fig. 21.8, p. 340
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Paleozoic Era (570-240 mya)

• Six periods
• Cambrian
• Ordovician
• Silurian
• Devonian
• Carboniferous
• Permian

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Paleozoic Era

• By early Paleozoic, diverse organisms of all six
  kingdoms lived in seas
• During the Silurian and Devonian, plants and
  animals invaded the land
• Ended with the greatest known mass extinction and
  the formation of Pangea

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Cambrian Period

• Explosive radiation of marine organisms
• Mass extinction near end of period
• May have resulted from cooling of seas

Gondwana
Page 336
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Ordovician Period

• Adaptive radiation of new reef organisms in warm,
  shallow seas
• Increase in diversity of shelled animals
• Ended with glaciation and mass extinction as
  Gondwana straddled South Pole

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Silurian into Devonian

• Reef communities recover

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First land plants
Figure 20.13 Page 337
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Devonian Vertebrates

• Jawed fishes arise, diversify
• Ancestors of amphibians onto land
• Radiation of amphibians begins
• Period ends with another mass extinction

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Carboniferous Period

• Sea levels swing widely
• Amphibians diversify
• First reptiles
• Seedless vascular plants and gymnosperms thrive

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Permian Period

• Insects, amphibians, and early reptiles in swamp
  forests
• Ends with greatest known mass extinction

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Figure 20.13 Page 337
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The Mesozoic Era

• Divided into three periods
• Triassic
• Jurassic
• Cretaceous
• The Age of the Reptiles
• Major geologic event was breakup of Pangea

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Triassic Period

• Seas repopulated after Permian extinction
• First dinosaurs and mammals
• Ends with a mass extinction

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A therapsid
Figure 20.15  Page 339
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Jurassic Period
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• Radiation of the dinosaurs
• Ended with a mass extinction that ended many
  dinosaur lineages

ichthyosaur
Figure 20.15  Page 339
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Cretaceous Period

• Surviving dinosaurs diversify
• Seedless plants and gymnosperms begin to decline

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Figure 20.15  Page 339
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Rise of Flowering Plants

• Conifers and other gymnosperms were dominant in
  early Mesozoic
• Angiosperms arose during the late Jurassic or the
  early Cretaceous
• In less than 40 million years, they displaced
  conifers and related plants in most environments

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Rise of the Angiosperms
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• Angiosperms arose during the late Jurassic or
  early Cretaceous
• In less than 40 million years, they displaced
  conifers and related plants in most environments
  

angiosperms
150
number of genera
100
ferns
cycads
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conifers
ginkgos
other genera
0
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100
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Figure 20.14Page 338
millions of years ago
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K-T Asteroid Impact Theory

• An asteroid impact caused mass extinction
  CretaceousTertiary (KT) boundary
• Iridium
• Impact crater in present Gulf of Mexico

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Global Broiling Hypothesis

• Energy released at the KT impact site was
  equivalent to detonating 100 million nuclear
  bombs
• Most animals and plants in open were destroyed
• Provided opportunity for the mammalian adaptive
  radiation

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Cenozoic Era

• Continents collided and mountain ranges arose
• Mammals underwent adaptive radiation
• Tropical forests gave way to woodlands and
  grasslands
• Most recent Ice Age occurred
• Humans set stage for possible mass extinction

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Paleocene to Eocene

• Tropical forests and subtropical forests extended
  as climates warmed
• Mammalian lineage diversified

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Later Cenozoic

• Climates became cooler and drier
• Grasslands and woodlands dominated
• Grazing and browsing animals thrived

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Dry woodland of Pleistocene
Figure 20.17bPage 341
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At Present

• Distribution of land masses favors high
  biodiversity
• Tropical forests are richest ecosystems
• In midst of what may be a great mass extinction
• Human hunters and human activities have increased
  the pace of extinction