The Origin and Evolution of Life

1
The Origin and Evolution of Life

• Chapter 20

2
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

3
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)

4
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

5
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

6
First Atmosphere

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

7
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

8
Stanley Millers Experiment
electrodes
to vacuum pump
spark discharge
CH4 NH3 H2O H2
gases
water out
condenser
water in
water droplets
water containing organic compounds
boiling water
Figure 20.3 b Page 326
liquid water in trap
9
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
10
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

11
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

12
Possible Sequence
membrane-bound proto-cells
self-replicating system enclosed in a selectively
permeable, protective lipid sphere
Figure 20.5  Page 331
13
Proterozoic Eon

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

14
The First Cells

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

15
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
16
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
17
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
18
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

19
Paleozoic Era (570-240 mya)

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

20
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

21
Cambrian Period

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

Gondwana
Page 336
22
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

23
Silurian into Devonian

• Reef communities recover

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First land plants
Figure 20.13 Page 337
24
Devonian Vertebrates

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

25
Carboniferous Period

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

26
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
27
The Mesozoic Era

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

28
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
29
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
30
Cretaceous Period

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

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Figure 20.15  Page 339
31
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

32
Rise of the Angiosperms
250
200

• 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
50
conifers
ginkgos
other genera
0
160
140
120
100
80
60
Figure 20.14Page 338
millions of years ago
33
K-T Asteroid Impact Theory

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

34
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

35
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

36
Paleocene to Eocene

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

37
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
38
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