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The Tree of Life
Chapter 26
Origins of Life
• Cell is the basic unit of life
• Today all cells come from pre-existing cells
• Earth formed ~4.5 billion years ago (BYA)
– As it cooled, chemically-rich oceans were formed from
water condensation
• Life arose spontaneously
– Ocean’s edge, hydrothermal deep-sea vents, or
elsewhere
2
3
Fundamental Properties of Life
• Cellular organization
• Sensitivity
• Growth
• Development
• Reproduction
• Regulation
• Homeostasis
• Heredity
• Panspermia
– Earth may have been “infected” with life from some
other planet
– Meteor or cosmic dust may have carried complex
organic molecules to earth
– Kicked off evolution of life
4
Conditions on Early Earth
• First organisms emerged ~3.5 BYA
• Seems likely that Earth’s first organisms
emerged and lived at very high temperatures
• Early atmosphere composition not agreed on
– May have been a reducing atmosphere
– Would have made it easier to form carbon-rich
molecules
5
• In 1953, Miller and Urey did an experiment
that reproduced early atmosphere
– Assembled reducing atmosphere rich in
hydrogen with no oxygen gas
– Atmosphere placed over liquid water
– Temperature below 100ºC
– Simulate lightning with sparks
6
7
• Methane gas (CH4) converted into other
simple carbon compounds
– Compounds combined to form simple
molecules and then more complex molecules
• Later experiments produced more than 30
carbon compounds including amino acids
– Adenine also produced
8
• RNA may have been first genetic material– Ribozyme activity
• Amino acids polymerized into proteins
• Metabolic pathways emerged– Primitive organisms may have been autotrophic –
built what they needed
• Lipid bubbles could increase the probability ofmetabolic reactions– Leads to cell membranes
• Other innovations contributed to diversity of life
9 10
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Periods
Eo
ns
Era
s
Late
Middle
Early
Late
Middle
Early
500 MYA
1000 MYA
1500 MYA
2000 MYA
2500 MYA
3000 MYA
3500 MYA
4000 MYA
4500 MYA
Pro
tero
zo
icA
rch
aean
Had
ean
Pre
cam
bri
an
Appearance of animals and plants
First multicellular organisms
Oldest definite fossils of eukaryotes
Appearance of oxygen in atmosphere
Cyanobacteria
Oldest fossils of prokaryotes
Molten-hot surface of Earth becomes somewhat cooler
Oldest rocks
Formation of Earth
Supercontinent of
Gondwana forms.
Oceans cover
much of North
America. Climate
not well known.
Most of Earth
is covered in
ocean and ice.
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Periods
Eo
ns
Era
s
Quaternary
Tertiary
Cretaceous
Jurassic
Triassic
Permian
Carbonife-
rous
Devonian
Silurian
Ordovician
Cambrian
Present
50 MYA
100 MYA
150 MYA
200 MYA
250 MYA
300 MYA
350 MYA
400 MYA
450 MYA
500 MYA
Cen
ozo
icM
eso
zo
icP
ale
ozo
ic
Ph
an
ero
zo
ic
Appearance of humans
First primate
Bird radiation
Mammal radiation
Pollinating insects
Diversification of flowering plants
First flowering plants, birds,
marsupial mammals
First dinosaurs
First gymnosperms
First reptiles
First amphibians
Bony fish, tetrapods, seed plants,
and insects appear
Early vascular plants diversify
Invertebrates dominate
First land plants
Cambrian explosion; increase in diversity
North and SouthAmerica joined
by land bridge.
Uplift of the
Sierra Nevada.
Worldwide glaciation.
Gondwana begins
to break apart;interior less arid.
Pangea intact.
Interior of Pangea
arid. Climate
very warm.
Supercontinent ofLaurentia to the
north and
Gondwana to the
south. Climate mild.
GondwanaGondwana
LaurentiaLaurentia
GondwanaGondwana
11 12
Grouping Organisms
6 kingdom system
Prokaryotes Eukaryotes
• 3 domain system
– Domain Archaea
– Domain Bacteria
– Domain Eukarya
13
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a.
Domain
Bacteria
(Bacteria)
Domain
Archaea
(Archaebacteria)
Domain
Eukarya
(Eukaryotes)
Common Ancestor
14
• Tree based on rRNA analysis
• Archaea and Eukarya are more closely related to each
other than to bacteria
15
Bacteria
• Most abundant organisms on Earth
• Key roles in biosphere
– Extract nitrogen from the air, and recycle
carbon and sulfur
– Perform much of the world’s photosynthesis
• Responsible for many forms of disease
• Highly diverse
• Most taxonomists recognize 12–15
different groups16
Archaea
• Shared characteristics
– Cell walls lack peptidoglycan (found in bacteria)
– Membrane lipids are different from all other organisms
– Distinct rRNA sequences
• Divided into three general categories
– Methanogens
– Extremophiles
– Nonextreme archaea
17
Eukarya
• Prokaryotes ruled the earth for at least one
billion years
• Eukaryotes appeared about 2.5 BYA
• Their structure and function allowed
multicellular life to evolve
• Eukaryotes have a complex cell
organization
– Extensive endomembrane system divides the
cell into functional compartments18
• Mitochondria and
chloroplasts most likely
arose by
endosymbiosis
• Mitochondria were
derived from purple
nonsulfur bacteria
• Chloroplasts from
cyanobacteria
19
Archaebacteria Animalia Fungi Protista Plantae Bacteria
Brown
algae
Photosynthetic
protists
Thermophiles
Halophiles
Methanogens
Ancestral
eukaryotic cell
Purple
bacteria
Photosynthetic
bacteriaOther
bacteria
Chloroplasts
Mitochondria
Red
algaeGreen
algae
Nonphotosynthetic
protists
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20
Viruses
• Are literally “parasitic” chemicals
– DNA or RNA wrapped in protein
• Cannot reproduce on their own
• Not considered alive – cannot be placed in
a kingdom
• Viewed as detached fragments of a
genome
21 22
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T4 bacteriophage
Ebola virus
100 nm
Vaccinia virus
(cowpox)
Influenza
virus
Tobacco mosaic
virus (TMV)
Herpes simplex
virus
HIV-1
(AIDS)
Rhinovirus
(common
cold)
Adenovirus
(respiratory
virus)
Poliovirus
(polio)
