Chapter 25 The History of Life on Earth

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Chapter 25 The History of Life on Earth
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Antarctica many millions of years ago
Antarctica now WOW!!
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• Past organisms were very different from todays.
• The fossil record shows macroevolutionary changes
  over large time scales including
• The origin of photosynthesis
• The emergence of terrestrial vertebrates
• Long-term impacts of mass extinctions

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Prebiotic Chemical Evolution the Origin of Life

• Hypothesis First cells originated by chemical
  evolution
• non living materials became organized into
  molecules molecules were able to replicate
  metabolize.
• possible because atmosphere was really different
  no O2, volcanoes, UV, lightning, etc.
• Four Main Stages of Cell Emergence
• small organic molecules are made abiotically
• monomers ? polymers (macromolecules)
• protocells (droplets of aggregated molecules)
• Origin of self replicating molecules/ beginning
  to heredity

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Stage 1 Synthesis of Organic Compounds on Early
Earth

• Earth formed about 4.6 bya
• Earths early atmosphere likely contained water
  vapor and chemicals released by volcanic
  eruptions (nitrogen, nitrogen oxides, carbon
  dioxide, methane, ammonia, hydrogen, hydrogen
  sulfide)

TED Talk The Line Between Life and Non-life
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• A. I. Oparin J. B. S. Haldane hypothesized that
  the early atmosphere was a reducing environment
  (no oxygen)
• Stanley Miller and Harold Urey conducted lab
  experiments that showed that the abiotic
  synthesis of organic molecules in a reducing
  atmosphere is possible
• Primeval Soup Hypothesis

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OR Organic compounds were created near
hydrothermal vents OR They rained down from
outer space
Video Hydrothermal Vent
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Stage 2 Abiotic Synthesis of Macromolecules

• What came first, the amino acid or the enzyme?
• How would macromolecules form without
  enzymes/dehydration synthesis?
• Dilute solutions containing monomers dripped onto
  hot sand, clay, or rock vaporizes water
• Proteinoids (proteins formed abiotically) were
  made this way
• Maybe waves splashed monomers onto hot lava?

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Stage 3 Protocells

• Replication metabolism are key properties of
  life
• Protocellss are aggregates of abiotically
  produced molecules surrounded by a membrane or
  membrane-like structure
• Exhibit
• simple reproduction
• metabolism
• maintain an internal chemical environment

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Protocells can behave similarly to a cell
(osmotic swelling, membrane potential like nerve
cell)
Glucose-phosphate
20 µm
Glucose-phosphate
Phosphatase
Starch
Amylase
Phosphate
Maltose
Maltose
(a) Simple reproduction by liposomes (aggregates
of lipids)
(b) Simple metabolism Possible to contain enzyme
within catalyze RXNs, give off product
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Stage 4 Self-Replicating RNA and the Dawn of
Natural Selection

• RNA probably the first genetic material, then
  DNA
• Ribozymes can make complementary copies of short
  stretches of their own sequence or other short
  pieces of RNA
• Base sequences provide blueprints for amino acid
  sequence (polypeptides)

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• Early protocells with self-replicating, catalytic
  RNA would have been more effective at using
  resources (fitness) would have increased in
  due to natural selection.
• RNA could have provided template for DNA (more
  stable, better at replicating)

The stage has now been set for life!
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Fig. 25-7
Ceno- zoic
Meso- zoic
Humans
Paleozoic
Colonization of land
Animals
Origin of solar system and Earth
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4
Proterozoic
Archaean
Prokaryotes
years ago
Billions of
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2
Multicellular eukaryotes
Single-celled eukaryotes
Atmospheric oxygen
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Fig. 25-4
Rhomaleosaurus victor, a plesiosaur
Present
Dimetrodon
100 million years ago
Casts of ammonites
175
200
270
300
Hallucigenia
4.5 cm
375
Coccosteus cuspidatus
400
1 cm
Dickinsonia costata
500
525
2.5 cm
565
Stromatolites
Tappania, a unicellular eukaryote
600
3,500 1,500
Fossilized stromatolite
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Table 25-1
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Table 25-1a
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Table 25-1b
Animation The Geologic Record
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Fig 25-UN2
1
4
Billions of
years ago
3
2
Prokaryotes
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The First Single-Celled Organisms

• Oldest known fossils are stromatolites
• rock-like structures composed of many layers of
  bacteria and sediment
• Dated 3.5 billion years ago
• Prokaryotes were Earths sole inhabitants from
  3.5 to about 2.1 billion years ago

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Fig. 25-4i
Stromatolites
3.5 BYA
Fossilized stromatolite
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Fig 25-UN3
1
4
Billions of
years ago
2
3
Atmospheric oxygen
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Photosynthesis the Oxygen Revolution

• By about 2.7 bya, O2 began accumulating in the
  atmosphere rusting iron-rich terrestrial rocks
• O2 produced by oxygenic photosynthesis reacted
  with dissolved iron and precipitated out to form
  banded iron formations
• Oxygen revolution rapid increase in O2 around
  2.2 bya
• Posed a challenge for life some microbes hid out
  in anaerobic environments
• Provided opportunity to gain energy from light
• Allowed organisms to exploit new ecosystems as
  old ones died, opening up new niches
• Source of O2 was likely bacteria similar to
  modern cyanobacteria
• Later rapid increase attributed to evolution of
  eukaryotes

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Fig. 25-8
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Fig 25-UN4
1
4
Billions of
years ago
3
2
Single- celled eukaryotes
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The First Eukaryotes

• Oldest fossils of eukaryotes go back 2.1 bya
• Endosymbiosis
• mitochondria plastids (chloroplasts related
  organelles) were formerly small prokaryotes
  living within larger host cells
• At first, undigested prey or internal parasites?
• 2 became interdependent host endosymbionts
  became a single organism

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• Evidence supporting endosymbiosis
• Similarities in inner membrane structures and
  functions between chloroplasts/mitochondria and
  prokaryotes
• Organelle division is similar to prokaryotes
• Organelles transcribe translate their own DNA
• Organelle ribosomes are more similar to
  prokaryotic ribosomes than eukaryotic ribosomes

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Fig. 25-4h
1.5 BYA
Tappania, a unicellular eukaryote
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The Origin of Multicellularity

• eukaryotic cells allowed for a greater range of
  unicellular forms
• Once multicellularity evolved then algae,
  plants, fungi, and animals
• Ancestor appeared rougly 1.5 bya, though oldest
  fossil is algae dated to 1.2 bya

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• Ediacaran biota (Proterozoic Eon)
• large more diverse soft-bodied organisms that
  lived from 565 to 535 mya after snowball Earth
• Thaw opened up niches that allowed for speciation

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Fig. 25-4g
565 MYA
2.5 cm
Dickinsonia costata
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Fig 25-UN6
Animals
1
4
Billions of
years ago
3
2
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The Cambrian Explosion

• sudden appearance of fossils resembling modern
  phyla in the Cambrian period (Phanerozoic Eon,
  535 to 525 mya)
• first evidence of predator-prey interactions
  claws, hard-shells, spikes, etc.

Burgess Shale
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Fig. 25-4f
525 MYA
1 cm
Hallucigenia
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Fig. 25-4e
400 MYA
4.5 cm
Coccosteus cuspidatus
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Fig. 25-10
500
Sponges
Cnidarians
Annelids
Molluscs
Chordates
Arthropods
Brachiopods
Echinoderms
Early Paleozoic era (Cambrian period)
Millions of years ago
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Late Proterozoic eon
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Fig 25-UN7
Colonization of land
1
4
Billions of
years ago
3
2
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The Colonization of Land

• Fungi, plants, and animals began to move to land
  500 mya
• Plants fungi 420 mya adaptations to reproduce
  on land
• Arthropods tetrapods are the most widespread
  and diverse land animals
• Tetrapods evolved from lobe-finned fishes around
  365 million years ago
• Amphibians, reptiles, then birds and mammals

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Fig 25-UN8
1.2 bya First multicellular eukaryotes
535525 mya Cambrian explosion (great
increase in diversity of animal forms)
500 mya Colonization of land by fungi,
plants and animals
2.1 bya First eukaryotes (single-celled)
3.5 billion years ago (bya) First prokaryotes
(single-celled)
500
1,000
1,500
2,000
3,000
2,500
3,500
4,000
Present
Millions of years ago (mya)
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Major Influences on Life on Earth

• Continental Drift 3 occasions of formation, then
  separation of supercontinents next one will
  occur in roughly 250 million years.
• Collision and separation of oceanic and
  terrestrial plates shape mountains, cause
  earthquakes
• Pangaea (250 mya) caused drastic changes in
  habitats evolution!
• Mass extinctions 5 major ones in Earths
  history
• Opens up niches for future species
• Usually takes 5-10 million years to return
  diversity to its pre-extinction levels
• Adaptive Radiation Periods of evolutionary
  change in which groups of organisms form many new
  species whose adaptations allow them to fill
  different niches (with little competition)

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Adaptive Radiation

• Occur after mass extinctions
• Rise of mammals after Cretaceous extinction
• Colonized regions (i.e. new islands)
• Hawaiian Islands

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How can evolutionary novelties/major changes in
form come about?

• Evolutionary developmental biology, or evo-devo,
  is the study of the evolution of developmental
  processes in multicellular organisms
• Genomic information shows that minor differences
  in gene sequence or regulation can result in
  major differences in form
• think fruit flies with legs instead of antennae

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Evo-devo

• allometric growth

• Changes in rate and timing (regulation) of
  developmental genes is called heterochrony
• Accelerated growth in bone structures (finger
  bones to wings in bats) or slowed growth
  (reduction in leg bones in whale ancestors)
• Paedomorphosis fast development of reproductive
  system compared to other development leads to
  maintenance of juvenile features though sexually
  mature (phenotypic variation)

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Newborn
Adult
5
2
Age (years)
(a) Differential growth rates in a human
Chimpanzee fetus
Chimpanzee adult
Human adult
Human fetus
(b) Comparison of chimpanzee and human skull
growth
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More Evo-devo
Fig. 21-17
Adult fruit fly

• Changes in spatial pattern of developmental genes
  (homeotic genes master regulatory genes)
• determine where, when, and how body segments
  develop
• Small changes in regulatory sequences of certain
  genes lead to major changes in body form

Fruit fly embryo (10 hours)
Fly chromosome
Mouse chromosomes
Mouse embryo (12 days)
Adult mouse
Hox genes of the fruit fly and mouse show the
same linear sequence on the chromosomes
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• Homeobox/Hox genes code for transcription factors
  that turn on developmental genes in embryos
• The expression of 2 Hox genes in snakes
  suppresses the development of legsthe same genes
  are expressed in chickens in the area between
  their limbs

• Change in location of two Hox genes in
  Crustaceans led to the conversion of swimming
  appendage to feeding appendage
• Duplications of Hox genes in vertebrates may have
  influenced the evolution of vertebrates from
  invertebrates

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Even more Evo-devo

• Changes in genes and where they are expressed
• Differing patterns of Hox gene expression
  variation in segmentation
• Suppression of leg formation in insects vs.
  crustaceans
• Change in expression, not gene, can cause
  differences in form

Brine shrimp Artemia in comparison to grasshopper
Hox expression
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Fig. 25-23
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Evolutionary Novelties are actually just new
forms arising by slight modifications of existing
forms
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