The Origin and Evolutionary
History of Life
Chapter 21
Learning Objective 1
•
What conditions do geologists think
existed on early Earth?
Early Earth
The Origin of Life
•
Biologists generally agree
•
•
•
life originated from nonliving matter
by chemical evolution
Origin of life is difficult to test experimentally
•
testable hypotheses about chemical evolution
KEY CONCEPTS
•
Although there is no direct fossil evidence
of the origin of life, biochemical
experiments have demonstrated how
complex organic molecules, found in all
living organisms, may have formed
4 Requirements for
Chemical Evolution
1. Absence of oxygen
•
oxygen would oxidize abiotically produced
organic molecules
2. Energy
•
to form organic molecules
4 Requirements for
Chemical Evolution
3. Chemical building blocks
•
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water, minerals, gases in atmosphere
to form organic molecules
4. Sufficient time
•
for molecules to accumulate and react
Learn more about conditions on
early Earth by clicking on the
figure in ThomsonNOW.
Learning Objective 2
•
Contrast the prebiotic soup hypothesis and
the iron–sulfur world hypothesis
Chemical Evolution
•
Prebiotic soup hypothesis
•
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organic molecules formed near Earth’s
surface in “sea of organic soup” or on rock or
clay surfaces
Iron–sulfur world hypothesis
•
organic molecules produced at hydrothermal
vents in deep ocean floor
Miller and Urey’s
Experiment
Electrodes
NH3
CH4
H2
H2O
To
vacuum
Spark chamber
Condenser
Boiling
chamber
Heat source
Organic molecules
collect in the trap
Fig. 21-2, p. 449
Insert “Miller's reaction
chamber experiment”
Miller_Urey.swf
See the Miller–Urey experiment
unfold by clicking on the figure
in ThomsonNOW.
Learning Objective 3
•
What major steps are hypothesized to
have occurred in the origin of cells?
The Origin of Cells
•
Macromolecules
•
•
Protobionts (macromolecular assemblages)
•
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assembled from small organic molecules
formed from macromolecules
Cells
•
arose from protobionts
Microspheres
RNA World Model
•
RNA
•
•
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first informational molecule to evolve
progression toward self-reproducing cell
Natural selection at molecular level
•
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resulted in information sequence
DNA → RNA → protein
RNA Molecules
Large pool of
RNA molecules
Selection for ability
to catalyze a
chemical reaction
Molecules with some
ability to catalyze the
reaction
Amplification and mutation
to create large pool of
similar RNA molecules
Repeat the selection–
amplification–mutation
process
Molecules with best
ability to catalyze the
reaction
Fig. 21-4, p. 451
Large pool of
RNA molecules
Selection for ability
to catalyze a
chemical reaction
Molecules with some
ability to catalyze the
reaction
Amplification and mutation
to create large pool of
similar RNA molecules
Repeat the selection–
amplification–mutation
process
Molecules with best
ability to catalyze the
reaction
Stepped Art
Fig. 21-4, p. 451
Learning Objective 4
•
How did the evolution of photosynthetic
autotrophs affected both the atmosphere
and other organisms?
The First Cells
•
Prokaryotic heterotrophs
•
•
•
obtained organic molecules from environment
probably anaerobes
Autotrophs
•
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evolved later
produced organic molecules by photosynthesis
Photosynthesis
•
Generated oxygen in atmosphere
•
•
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changed early life
permitted evolution of aerobes
Aerobes
•
use oxygen for efficient cellular respiration
Ozone
2(O3)
Lower atmosphere Upper atmosphere
3(O2)
Fig. 21-6, p. 453
Ultraviolet rays
Sun
Learning Objective 5
•
What is the hypothesis of serial
endosymbiosis?
Serial Endosymbiosis
•
Eukaryotic cells arose from prokaryotic
cells
•
Certain eukaryotic organelles
(mitochondria, chloroplasts) evolved from
prokaryotic endosymbionts
•
incorporated within larger prokaryotic hosts
Serial Endosymbiosis
ORIGINAL
PROKARYOTIC
HOST CELL
Multiple invaginations of
the plasma membrane
Aerobic bacteria
become mitochondria
Photosynthetic
bacteria...
DNA
Aerobic bacteria
Endoplasmic reticulum
and nuclear envelope
form from the plasma
membrane invaginations
(not part of serial
endosymbiosis)
... become
chloroplasts
EUKARYOTIC
CELLS: PLANTS,
SOME PROTISTS
EUKARYOTIC
CELLS: ANIMALS,
FUNGI, SOME
PROTISTS
Fig. 21-7, p. 454
Insert “The endosymbiont
theory”
endosymbiont_theory_m.swf
Learn more about
endosymbiosis by clicking on
the figure in ThomsonNOW.
KEY CONCEPTS
•
Photosynthesis, aerobic respiration, and
eukaryotic cell structure represent several
major advances that occurred during the
early history of life
Learning Objective 6
•
What are the distinguishing organisms and
major biological events of the Ediacaran
period and the Paleozoic, Mesozoic, and
Cenozoic eras
Proterozoic Eon
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2500 mya to 542 mya
•
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life consisted of prokaryotes
About 2.2 bya
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first eukaryotic cells appeared
Ediacaran Period
•
Ediacaran period
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Ediacaran fossils
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600 mya to 542 mya
last period of Proterozoic eon
oldest known fossils of multicellular animals
Ediacaran fauna
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small, soft-bodied invertebrates
An Ediacaran Sea
The Paleozoic Era (1)
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Began about 542 mya
•
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lasted about 291 million years
Many plants and animals appeared
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all major plants (except flowering plants)
all animal phyla
reptiles
fishes and amphibians flourished
Cambrian Radiation
Fig. 21-9a, p. 457
Fig. 21-9b, p. 457
Fig. 21-9c, p. 457
Devonian Period
(b) Pterapsis
(c) Jamoytius
(a) Thelodus
Fig. 21-10, p. 458
Carboniferous Period
The Paleozoic Era (2)
•
Greatest mass extinction of all time
•
•
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at end of Paleozoic era (251 mya)
> 90% of marine species extinct
70% of land-dwelling vertebrate genera
many plant species
The Mesozoic Era
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Began about 251 mya
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lasted about 185 million years
Dinosaurs dominated
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reptiles diversified
insects flourished
flowering plants appeared
birds appeared
early mammals appeared
Triassic Period
Cretaceous Period
Cretaceous Period
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66 mya
•
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end of Cretaceous period
many species abruptly became extinct
Collision of extraterrestrial body with Earth
•
•
may have caused dramatic climate changes
resulted in mass extinction
Cenozoic Era
•
From 66 mya to present
•
•
flowering plants, birds, insects, mammals
diversified greatly
Late Miocene and Early Pliocene epochs
•
human ancestors appeared in Africa
The Fossil Record
Saurischians
Ilium
Hip socket
Pubis
Ischium
Coelophysis
The saurischian pelvis
Fig. 21-15a, p. 461
Ornithischians
Ilium
Hip socket
Pubis
Ischium
Stegosaurus
The ornithischian pelvis
Fig. 21-15b, p. 461
KEY CONCEPTS
•
The fossil record tells us much of what we
know about the history of life, such as
what kinds of organisms existed and
where and when they lived
Fossil Trilobites
KEY CONCEPTS
•
Certain organisms appear in the fossil
record, then disappear and are replaced
by others
Stromatolites
KEY CONCEPTS
•
Scientists identify and demonstrate
relationships among fossils in rock layers
from different periods of geologic time