Download Figure 26.1

Chapter 26
• The Tree of Life
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• Changing Life on a Changing Earth
• Life is a continuum extending from the earliest
organisms to the great variety of species that
exist today
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• Geological events that alter environments
– Change the course of biological evolution
• Conversely, life changes the planet that it
inhabits
Figure 26.1
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• Conditions on early Earth made the origin of
life possible
• Hypothesis:
– Chemical and physical processes on early
Earth produced very simple cells through a
sequence of stages
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• Earth formed ~ 4.6 billion years ago
• Earth’s early atmosphere
– Contained water vapor + many chemicals
released by volcanic eruptions
– Little or no O2  reducing atmosphere
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Miller – Urey experiment
• Lab simulations of early Earth atmosphere:
EXPERIMENT
Miller and Urey set up a closed system in their
laboratory to simulate conditions thought to have existed on early
Earth. A warmed flask of water simulated the primeval sea. The
strongly reducing “atmosphere” in the system consisted of H2,
methane CH4), ammonia (NH3), and water vapor. Sparks were
discharged in the synthetic atmosphere to mimic lightning. A
condenser cooled the atmosphere, raining water and any dissolved
compounds into the miniature sea.
Water vapor
CH4
Electrode
RESULTS
As material circulated through the apparatus,
Miller and Urey periodically collected samples for analysis. They
Condenser
identified a variety of organic molecules, including amino acids such
as alanine and glutamic acid that are common in the proteins of
organisms. They also found many other amino acids and complex,
oily hydrocarbons.
Cold
water
CONCLUSION
Organic molecules, a first step in the origin of
life, can form in a strongly reducing atmosphere.
Cooled water
containing
H2O
Figure 26.2
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organic
molecules
Sample for
chemical analysis
• First organic cmpds. may have formed near
submerged volcanoes and deep-sea vents
Figure 26.3
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• Some organic cmpds. may have come from
space
• Carbon cmpds. have been found in some of
the meteorites
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• Possibly, life is not restricted to Earth
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Abiotic synthesis
• Small organic molecules
– Polymerize when they are concentrated on hot
sand, clay, or rock
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• Protobionts
– Aggregates of abiotically produced molecules
surrounded by membrane
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• Protobionts could have formed spontaneously
from abiotically produced organic cmpds
• e.g., small membrane-bounded droplets called
liposomes form when lipids are added to water
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Glucose-phosphate
20 m
Glucose-phosphate
Phosphorylase
Starch
Amylase
Phosphate
Maltose
Maltose
Figure 26.4a, b
(a) Simple reproduction. This liposome is “giving birth” to smaller
liposomes (LM).
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(b) Simple metabolism. If enzymes—in this case,
phosphorylase and amylase—are included in the
solution from which the droplets self-assemble,
some liposomes can carry out simple metabolic
reactions and export the products.
The “RNA World” and the Dawn of Natural Selection
• The first genetic material
– probably RNA, not DNA
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• RNA molecules (ribozymes) catalyze many
different reactions, including
– Self-splicing
– Making copies of short stretches of their own
sequence
Ribozyme
(RNA molecule)
3
Template
Nucleotides
Figure 26.5
Complementary RNA copy
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5
5
• Early protobionts with self-replicating, catalytic
RNA
– used resources and increased in number
through natural selection
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• The fossil record chronicles life on Earth
• Study of fossils
– Window into the lives of organisms that existed
long ago, information about the evolution of life
over billions of years
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Fossil dating
• Sedimentary strata
– Reveal the relative ages of fossils
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• Index fossils
– Similar fossils found in the same strata in
different locations
– Strata at one location correlates w/ strata f/
another location
Figure 26.6
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• Absolute ages of fossils
Ratio of parent isotope
to daughter isotope
– Determined by radiometric dating
Accumulating
“daughter”
isotope
1
2
Remaining
“parent”
isotope
1
Figure 26.7
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14
18
2
Time (half-lives)
3
1 16
4
•
Magnetic reversals of the north and south
magnetic poles
–
Have occurred repeatedly in the past
–
 record on rocks throughout the world
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• Geologic record divided into
– Three eonsand many eras and periods
• Time periods
– Mark major changes in the composition of
fossil species
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Table 26.1
• Geologic record
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Mass Extinctions
– Rapid global environmental changes  a
majority of species were swept away
Millions of years ago
600
400
500
300
200
100
0
2,500
100
Number of
taxonomic
Permian mass families
extinction
80
2,000
Extinction rate (
60
1,500
40
1,000
Cretaceous
mass extinction
Number of families (
)
Extinction rate
)
500
20
Paleozoic
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Mesozoic
Paleogene
Cretaceous
Jurassic
Triassic
Permian
Carboniferous
Devonian
Ordovician
Silurian
Cambrian
Proterozoic eon
Figure 26.8
Cenozoic
Neogene
0
0
Major mass extinctions
•
The Permian extinction
–
Claimed 96% of marine animal species and 8
out of 27 orders of insects
–
Possibly caused by enormous volcanic
eruptions
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• Cretaceous (KT) extinction
– Doomed many marine and terrestrial
organisms, notably dinosaurs
– Likely/ possibly caused by the impact of a
meteor
NORTH
AMERICA
Yucatán
Peninsula
Chicxulub
crater
Figure 26.9
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• After mass extinctions  adaptive radiations
into newly vacated ecological niches
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• Analogy of a clock
– places major events in the Earth’s history in
the context of the geological record
Cenozoic
Humans
Land plants
Origin of solar
system and
Earth
Animals
4
1
Proterozoic Archaean
Eon
Eon
Billions of years ago
2
3
Multicellular
eukaryotes
Figure 26.10
Single-celled
eukaryotes
Prokaryotes
Atmospheric
oxygen
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• As prokaryotes evolved, they exploited and
changed young Earth
• Oldest known fossils are stromatolites
– Rocklike structures w/ many layers of bacteria
and sediment
– 3.5 billion years old
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(a) Lynn Margulis (top right), of the University of Massachussetts, and
Kenneth Nealson, of the University of Southern California, are
shown collecting bacterial mats in a Baja California lagoon. The
mats are produced by colonies of bacteria that live in environments
inhospitable to most other life. A section through a mat (inset)
shows layers of sediment that adhere to the sticky bacteria as
the bacteria migrate upward.
(b) Some bacterial mats form rocklike structures called stromatolites,
such as these in Shark Bay, Western Australia. The Shark Bay
stromatolites began forming about 3,000 years ago. The inset
shows a section through a fossilized stromatolite that is about
Figure 26.11a, b 3.5 billion years old.
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• Prokaryotes were Earth’s sole inhabitants
– From 3.5 to about 2 billion years ago
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• Electron transport systems of a variety of types
– Essential to early life
– Some aspects that possibly precede life itself
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Photosynthesis and the Oxygen Revolution
• Earliest types of photosynthesis
– Did not produce O2
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• Oxygenic photosynthesis
– Evolved ~ 3.5 bya in cyanobacteria
Figure 26.12
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• O2 began to accumulate in the atmosphere ~
2.7 bya
– Challenge for life
– Opportunity to gain energy f/ light
– Allowed organisms to exploit new ecosystems
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•
Eukaryotic cells arose from symbioses and
genetic exchanges between prokaryotes
•
Question?? how eukaryotic cells evolved
from much simpler prokaryotes
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• Oldest fossils of eukaryotic cells
– 2.1 billion years
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• Endosymbiosis
– Mitochondria and plastids were formerly small
prokaryotes living within larger host cells
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• Probably undigested prey or internal parasites
Cytoplasm
DNA
Plasma
membrane
Ancestral
prokaryote
Infolding of
plasma membrane
Endoplasmic
reticulum
Nucleus
Nuclear envelope
Engulfing
of aerobic
heterotrophic
prokaryote
Cell with nucleus
and endomembrane
system
Mitochondrion
Mitochondrion
Engulfing of
photosynthetic
prokaryote in
some cells
Ancestral
heterotrophic
eukaryote
Figure 26.13
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Plastid
Ancestral
Photosynthetic
eukaryote
• Eventually host and endosymbionts would
have become a single organism
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• Supporting evidence:
– Similar inner membrane structures and
functions
– Both have their own circular DNA (genes)
– Own ribosomes
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Eukaryotic Cells as Genetic Chimeras
• Additional endosymbiotic events and horizontal
gene transfers
–  large genomes and complex structures
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• Eukaryotic flagella and cilia
– May have evolved f/ symbiotic bacteria,
50 m
Figure 26.14
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• Multicellularity evolved several times
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• Molecular clocks date the common ancestor of
multicellular eukaryotes to 1.5 billion years
• Oldest known fossils of eukaryotes ~ 1.2 bya
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• Chinese paleontologists recently described
570-million-year-old fossils
– probably animal embryos
Figure 26.15a, b
(a) Two-cell stage
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150 m
(b) Later stage
200 m
• The first multicellular organisms were colonies
– Collections of autonomously replicating cells
Figure 26.16
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10 m
• Some cells in the colonies
– Became specialized for different functions
• The first cellular specializations
– Had already appeared in the prokaryotic world
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The “Cambrian Explosion”
• Most of the major phyla of animals
– Appear ‘suddenly’ in the fossil record that was
laid down during the first 20 million years of the
Cambrian period
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• 2 animal phyla, Cnidaria and Porifera
Early
Paleozoic
era
(Cambrian
period)
Millions of years ago
542
Late
Proterozoic
eon
Figure 26.17
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Arthropods
Molluscs
Annelids
Brachiopods
Chordates
Echinoderms
Cnidarians
500
Sponges
– Are older, dating from the late Proterozoic
• Molecular evidence
– Suggests that many animal phyla originated
and began to diverge much earlier, between
1 billion and 700 million years ago
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• Plants, fungi, and animals
– Colonized land about 500 million years ago
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• Symbiotic relationships between plants and
fungi
– Are common today and date from this time
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Continental Drift
• Earth’s continents are not fixed
– They drift across our planet’s surface on great
plates of crust that float on the hot underlying
mantle
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• Often, these plates slide along the boundary of
other plates
– Pulling apart or pushing against each other
Eurasian Plate
North
American
Plate
Juan de Fuca
Plate
Caribbean
Plate
Philippine
Plate
Arabian
Plate
Indian
Plate
Cocos Plate
Pacific
Plate
Nazca
Plate
South
American
Plate
Scotia Plate
Figure 26.18
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African
Plate
Australian
Plate
Antarctic
Plate
• Many important geological processes
– Occur at plate boundaries or at weak points in
the plates themselves
Volcanoes and
volcanic islands
Oceanic ridge
Trench
Figure 26.19
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• The formation of the supercontinent Pangaea
during the late Paleozoic era
India collided with
Eurasia just 10 million
years ago, forming the
Himalayas, the tallest
and youngest of Earth’s
major mountain
ranges. The continents
continue to drift.
Eurasia
65.5
Millions of years ago
– And its breakup during
the Mesozoic era explain
many biogeographic puzzles
Cenozoic
0
Africa
South
America
Antarctica
Laurasia
Mesozoic
135
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Paleozoic
251
Figure 26.20
India
Madagascar
By the end of the
Mesozoic, Laurasia
and Gondwana
separated into the
present-day continents.
By the mid-Mesozoic,
Pangaea split into
northern (Laurasia)
and southern
(Gondwana)
landmasses.
At the end of the
Paleozoic, all of
Earth’s landmasses
were joined in the
supercontinent
Pangaea.
• New information has revised our understanding
of the tree of life
• e.g. Molecular (e.g. DNA, protein) Data
– insights to deepest branches of the tree of life
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• Early classification systems had two kingdoms
– Plants and animals
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• Robert Whittaker’s system with five kingdoms
– Monera, Protista, Plantae, Fungi, and Animalia
Plantae
Fungi
Protista
Figure 26.21
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Monera
Animalia
Reconstructing the Tree of Life: A Work in Progress
• A three domain system
– Has replaced the five kingdom system
– Includes the domains Archaea, Bacteria, and
Eukarya
• Each domain
– Has been split by taxonomists into many
kingdoms
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Figure 26.22
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Domain Archaea
Domain Bacteria
Universal ancestor
Domain Eukarya
Charophyceans
Chlorophytes
Red algae
Cercozoans, radiolarians
Stramenopiles (water molds, diatoms, golden algae, brown algae)
Chapter 27
Alveolates (dinoflagellates, apicomplexans, ciliates)
Euglenozoans
Diplomonads, parabasalids
Euryarchaeotes, crenarchaeotes, nanoarchaeotes
Korarchaeotes
Gram-positive bacteria
Cyanobacteria
Spirochetes
Chlamydias
Proteobacteria
• One current view of biological diversity
Chapter 28
Figure 26.21
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Plants
Fungi
Animals
Bilaterally symmetrical animals (annelids,
arthropods, molluscs, echinoderms, vertebrates)
Cnidarians (jellies, coral)
Chapter 32
Sponges
Chapter 31
Choanoflagellates
Club fungi
Sac fungi
Chapter 28
Arbuscular mycorrhizal fungi
Zygote fungi
Chytrids
Chapter 30
Amoebozoans (amoebas, slime molds)
Angiosperms
Gymnosperms
Seedless vascular plants (ferns)
Bryophytes (mosses, liverworts, hornworts)
Chapter 29
Chapters 33-49