Download History of Life on Earth

History of Life on Earth
Biology Chapter 12
Ms. Pollock
Spring 2008
How Did Life Begin?
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Earth believed 4.5 billion years old
Began as fiery ball of molten rock
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Cooled and formed rocky crust
Water vapor in atmosphere condensed to form
oceans, where first life believed to have developed
Timeline of development created using
radiometric dating
How Did Life Begin?
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Life thought to have begun as the result of
interactions between nonliving matter
First billion years of Earth’s existence
Simple organic molecules created and
energized by the sun and volcanic heat
Molecules combined to create new, more
complex molecules
Primordial Soup
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1920s model suggested by Russian A.I. Oparin
and British scientist J.B.S. Haldane
Early oceans containers of large amounts of
organic molecules, like vegetables in soup
Compounds formed by spontaneous reactions
energized by solar radiation, volcanic eruption, or
lightning
Atmosphere believed to be lacking in oxygen
Tested in 1953 by Stanley Miller and determined
possible under correct conditions
The Bubble Model
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1986 Louis Lerman suggested key processes
for life formation occurred in bubbles on ocean
surface
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Gases from volcanic eruptions trapped in
underwater bubbles
Chemical reactions in bubbles, protected from UV
Bubbles rose and burst, releasing organics
Released organics exposed to air and UV to react
More complex molecules formed as processes
continued to cycle
The Evolution of Life
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Fossils studied to determine evolution of
organisms
Oldest known fossils 2.5 billion years old
Cyanobacteria first marine bacteria to appear
Photosynthetic cyanobacteria responsible for
development of oxygen in the atmosphere
Current atmosphere composed of 21% oxygen
Prokaryotes
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Two groups of prokaryotes developed early
Eubacteria with peptidoglycan in cell walls
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Reamining example E. coli
Many disease-causing bacteria
Archaebacteria with no peptidoglycan in cell
walls
Eukaryotes
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Appeared 1.5 billion years ago
Larger, more complex than prokaryotes
Mitochondria present in almost all
DNA enclosed in nucleus
Chloroplasts present in plants and some
protists
Origins of Mitochondria and
Chloroplasts
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Believed to be result of endosymbiosis
Proposed theory in 1966 by Lynn Margulis
Mitochondria believed descendants of
symbiotic, aerobic eubacteria and
choloroplasts descendants of symbiotic,
photosynthetic eubacteria
Bacteria entered cells and fulfilled roles of
cellular respiration or photosynthesis.
Believed to be cyanobacteria
Support for Endosymbiosis
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Size and structure of eubacteria and
mitochondria and chloroplasts
Genetic material similarities
Ribosomes
Reproduction by fission
Multicellularity
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Organisms grouped into six categories
Protists large group of both unicellular and
multicellular organisms
Protists considered important to development
of multi-cellular organisms
First multi-cellular organisms found in rocks
700 million years old
Three kingdoms resulted – Fungi, Plantae,
Animalia
Origins of Modern Organisms
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Most believed to have developed in short time
Precambrian and Cambrian periods
Time of great evolutionary expansion –
Burgess Shale in Canada evidence
Ordovician period next – great marine
diversity
Mass Extinctions
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Evidence in fossil record of sudden change at
end of Ordovician period
Many organisms extinct – 5 mass extinctions
in Earth’s history
Another mass extinction believed to be
occurring today due to rapid decline of
ecosystems
Humans believed cause of current extinction
The Theory of Evolution by Natural
Selection
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Idea of evolution first proposed by Roman
philosopher Lucretius
1859 English naturalist Charles Darwin
published evidence for evolution and
suggested a possible mechanism for the
process
Idea accepted by most scientists as basis for
diversity of life on Earth
Modern theory built on Darwin’s ideas
Before Darwin
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Belief by most people that each species a divine
creation that exists, unchanging, as it was created
Darwin’s grandfather a scientist who tried to explain
a mechanism for changes over time
1809 French scientist Jean Baptiste Lamarck
proposed hypothesis for change in organisms over
generations
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Changes in organisms due to use or disuse of features
Changes passed to offspring
Belief now known to be faulty
Darwin
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Wealthy family, father a doctor who wanted him to
be a doctor or a minister
Attended medical school in Scotland but hated
surgery, so he changed to become a minister
1831 recommended by professor as naturalist on
HMS Beagle
Read Charles Lyell’s Principles of Geology on trip
that proposed Earth’s surface changed gradually
over time and applied this belief to speciesi
Darwin
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Visited Galapogos Islands and noted
similarities between animals there and on
nearby coasts
Developed belief that ancestors of animals
migrated and then changed
Continued studies on return from voyage
Published many years later
Growth of Populations
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1798 English economist Thomas Malthus wrote that
human populations are able to increase faster than the
food supply.
Unchecked populations grow by geometric
progression, while food supplies grow by arithmetic
progression.
Human populations are checked by death due to
disease, war, and famine.
Darwin applied this belief to the theory of evolution.
Evolution by Natural Selection
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Limited offspring produced in lifetime, though
potential for more
Individuals with physical or behavioral traits
that better suit their environment are more
likely to survive and will reproduce more
successfully than those without the traits.
Natural selection
Adaptation result of challenges and
opportunities of different environments.
Publication of Darwin’s Work
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Darwin’s ideas finally written down in 1844
Recent publications about evolution were
harshly criticized, so Darwin waited to publish
his work until 1858, when a friend was also
attempting to be published
The papers were presented together at a
scientific meeting
Darwin’s Theory
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On the Origin of the Species by Means of
Natural Selection, November 1859
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Inherited variation within genes of every
population or species (random mutation,
translational errors)
Individuals of population better able to survive and
have offspring in a particular environment
Over time favorable traits spread in population
Evidence from fossils and other sources of
evolution of species from extinct organisms
Darwin’s Ideas Updated
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Darwin’s ideas reviewed since publication
New discoveries in genetics providing insight
into the way natural selection causes evolution
Genes responsible for inherited traits
Frequency of certain alleles altered by natural
selection
Sexual reproduction and recombination of
alleles key to new variations
Species Formation
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Differences in environment from place to place
Species evolved in different directions
Reproductive isolation prevents two
populations of the same species from breeding.
Species that become too different over time
incapable of producing offspring
Example – Kaibab squirrel on North Rim of
Grand Canyon and Abert squirrel on South
Rim of Grand Canyon
The Tempo of Evolution
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For decades evolution considered gradual
process that occurs continuously (gradualism)
Stephen Jay Gould and Niles Eldredge
(Americans) suggest successful species may be
unchanged for long periods of time
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Major environmental change cause of evolutionary
spurts
Periods of little or no change (punctuated
equilibrium)
Evidence of Evolution
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Fossil record
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Change recorded in rocks
Older rocks have different species than younger
rocks.
Three of Darwin’s points widely accepted
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Earth 4.5 billion years old
Organisms living on Earth for most of its history
All organisms today share ancestry with earlier,
simpler life-forms
Formation of Fossils
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Fossil record incomplete
Impossible to form fossils in every
environment
Hard tissue required
Decay rates vary among species.
Paleontologists scientists who study fossils
Fossils collected and lined up for progressive
study of organisms
Anatomy and Development
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Basic similarities in body structures, even
when functions differ
Vestigial structures evidence of organism’s
evolutionary past
Homologous structures share a common
ancestry, but they exist on two different
organisms.
Evolutionary history seen in embryo
development
Biological Molecules
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Amino acids expected to be similar between
organisms that evolved from the same ancestor
in the recent past
Evolutionary history based on large numbers
of gene sequences more reliable – go along
more accurately with fossil record
Examples of Evolution
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Environment key factor in determining
direction of change
Future environmental changes could change
the characteristics favorable for survival.
Four important points drive natural selection.
Factors in Natural Selection
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All populations have genetic variation.
The environment presents challenges to
successful reproduction.
Individuals tend to produce more offspring
than the environment can support.
Individuals that are better able to cope with the
challenges presented by their environment tend
to leave more offspring than those individuals
less suited to the environment do.
Example
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Tuberculosis (TB) is the infectious disease that
kills the most adults in the world.
In the 1950s, two antibiotics wiped out many
cases of TB and prevented its spread.
New antibiotic-resistant strains of TB have
developed, due to genetic variation.
The over-use of antibiotics can cause this
resistance.
Darwin’s Finches
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31 specimens of finches collected from three of
the Galapagos Islands
9 distinct species, all similar to each other, except
their bills (beaks)
2 ground finches with large bills to crush seeds, 2
narrow bills to eat insects, 1 fruit eater, 1 picks
insects from cacti, another drinks blood from sea
birds
All believed by Darwin to have evolved from one
species
Darwin’s Finches
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Changes in species as different populations
adapted to different food sources
Idea tested in 1938 and 1973 and found in
second study to be true
Numbers of birds with certain characteristics
changed by natural selection, as Darwin
suggested.
Formation of New Species
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Stages of species formation
Changes that improve reproductive success
favored by natural selection
Divergence is the accumulation of differences
between groups, which lead to formation of
new species.
The process of forming new species is
speciation.
Subspecies
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Different populations of species possibly
living in different environments
Offspring better suited to environment
developed through natural selection
In vastly different environments, populations
can become very dissimilar.
Leads to genetic differences and subspecies
Eventually different enough that interbreeding
impossible
Maintaining New Species
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Eventually new species different enough that
interbreeding impossible
Can be geographic isolation
Different reproduction times
Physical differences
Changes in attraction
Offspring possibly not fertile
Offspring possibly not suited to environment of either
parent