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Chapter 19
History of Life
19-1 The Fossil Record
What do fossils reveal about ancient life?
What are some types of fossils?
Where are fossils typically found?
What can fossils reveal?
– The structure of an organism and infer evolutionary relationships
– The environment in which an organism may have lived
– The ways in which the extinct animal may have lived
18-1 The Fossil Record
How do we date events in Earth’s history?
Relative Dating & Index Fossils
– Relative dating allows paleontologists to
determine whether a fossil is older or younger
than other fossils
– Index fossils are distinctive fossils used to
establish and compare the relative ages of
rock layers and the fossils they contain
– To be useful, an index fossil must be
easily recognized
occur in only a few rock layers and
be widely distributed
Strata of sedimentary rock at the Grand Canyon
Trilobites, a common index
fossil of the Cambrian period
Examples
of Index
Fossils
Found
During
Different
Time
Periods
An example of how index fossils are used
18-1 The Fossil Record
Radiometric Dating
Relies on radioactive isotopes which
decay at a particular rate
Half-life = the time it takes for ½ of the
radioactive material to decay
The proportion of radioactive to stable
isotopes is used to calculate the age of a
sample
18-1 The Fossil Record
Section 19-2
Patterns & Processes of
Evolution
Theories of the Mechanism of Evolution
Gradualism
– Evolution occurs at a slow constant rate
Punctuated Equilibrium
– Evolution occurs at an irregular rate through
geologic time
– See periods of long stability followed by the
sudden appearance of new forms
– Still requires thousands of years for the
formation of new species
Mechanisms of Evolution
Change
Gradualism
Punctuated
equilibrium
Time
Figure 24.17 Two models for the tempo of speciation
Patterns of Evolution
Divergence
– Organisms within a species become so
different they can no longer interbreed
Patterns of Evolution Leading to Speciation
Adaptive Radiation ( a special case of divergence)
– Process of dispersal, adaptation, and
subsequent speciation
– Ex: finches on the Galapagos Islands
migrated from South American mainland,
adapted to their new environment and
accumulated enough changes to generate a
new species
Adaptive
Radiation
Patterns of Evolution
Parallel Evolution
– Two species evolve in a similar manner due
to being subjected to similar environmental
pressures
– Example: African ostrich and South American
rhea
Rhea
Ostrich
Emu
Examples of parallel evolution
Patterns of Evolution cont’d
Convergence
– Two distantly related species evolve in a
similar manner due to being subjected to
similar environmental pressures
– Examples
bird wings and insect wings are analogous
structures that result from convergent
evolution
Torpedo shaped bodies of animals that
swim in water (seals, penguins, fish,
whales)
Convergent evolution and analogous structures
Some
examples of
convergent
evolution
Patterns of Evolution cont’d
Coevolution
– Two unrelated groups become uniquely
adapted to one another
– Often seen in the relationship between
flowering plants and the insects that pollinate
them
Figure 22.10 Camouflage as an example of evolutionary adaptation
Section 19-3
Mystery of Life’s Origins
What do scientists hypothesize about
early Earth and the origin of life?
Earth’s Early History
Earth
– may have evolved from condensed gases and
dust
– may be 4.6 billion years old
– early atmosphere very hot / composed of
volcanic gases such as methane (CH4),
carbon dioxide (CO2), ammonia (NH3),
hydrogen (H2), and water vapor (H2O) / free
oxygen (O2) was absent
Earth’s Early History
– energy from heat and lightening may have
allowed combinations of gases to form new
molecules such as amino acids, etc.
– 1952 Miller and Urey simulate early
atmospheric conditions in the laboratory and
generate amino acids
Miller and
Urey’s
Experiment
The First Cells
Q: How did we get from complex organic
molecules to living organisms?
A: No one knows for sure
Essential characteristics of life:
– Self-maintenance (maintain organization and
order)
– Self-replication (reproduce themselves)
The First Cells, cont’d
Thought that the first living things were
heterotrophs
Oldest microfossils are ~ 3 billion years
old
First photosynthetic organisms may have
been part autotroph/part heterotroph
Earliest photosynthetic organisms
probably did not produce free oxygen as a
by-product
The First Cells, cont’d
Anaerobic (without oxygen)
– Anaerobes use light energy to synthesize organic
compounds utilizing H2S instead of H2O
Aerobic (requires oxygen)
Eventually photosynthesis evolved as we know it
today
Prokaryotes vs Eukaryotes
– Theory that mitochondria and chloroplasts found in
eukaryotes originated as free-living prokaryotes that
were taken up by larger anaerobic prokaryotes
Endosymbiotic Hypothesis
Chloroplast
Aerobic
bacteria
Ancient Prokaryotes
Nuclear
envelope
evolving
Photosynthetic
bacteria
Plants
and
plantlike
protists
Mitochondrion
Primitive Photosynthetic
Eukaryote
Ancient Anaerobic
Prokaryote
Primitive Aerobic
Eukaryote
Animals, fungi,
and nonplantlike
protists
The First Cells, cont’d
Photosynthetic organisms that produced oxygen
(O2) as a by-product led to significant changes in
the Earth’s atmosphere
Free O2 reacted to form ozone (O3) which
prevents many of the sun’s UV rays from
reaching Earth as a by-product led to significant
changes in the Earth’s atmosphere
Is our atmosphere still evolving?
19-3 Earth’s Early History
Sexual Reproduction and Multicellularity
What is the evolutionary significance of sexual
reproduction?
The development of sexual reproduction sped
up evolutionary change because sexual
reproduction increases genetic variation