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Chapter 17 Notes- The History of Life pages 423-428, 435-440

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Chapter 17 Notes- The History of Life pages 423-428, 435-440 17 2 Earth s Early History A. Formation of Earth B. The First Organic Molecules – PowerPoint PPT presentation

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Title: Chapter 17 Notes- The History of Life pages 423-428, 435-440


1
Chapter 17 Notes- The History of Life pages
423-428, 435-440
  • 172 Earths Early History
  • A. Formation of Earth
  • B. The First Organic Molecules
  • C. How Did Life Begin?
  • 1. Formation of Microspheres
  • 2. Evolution of RNA and DNA
  • D. Free Oxygen
  • E. Origin of Eukaryotic Cells
  • F. Sexual Reproduction and Multicellularity
  • 174 Patterns of Evolution
  • A. Extinction
  • B. Adaptive Radiation
  • C. Convergent Evolution
  • D. Coevolution
  • E. Punctuated Equilibrium
  • F. Developmental Genes and Body Plans

2
Origins The Early Idea
  • In the past, the ideas that decaying meat
    produced maggots, mud produced fishes, and grain
    produced mice were reasonable explanations for
    what people observed occurring in their
    environment.
  • Such observations led people to believe in
    spontaneous generationthe idea that nonliving
    material can produce life.

3
Spontaneous generation is disproved
  • In 1668, an Italian physician, Francesco Redi,
    disproved a commonly held belief at the timethe
    idea that decaying meat produced maggots, which
    are immature flies.
  • However, during Redis time, scientists began to
    use the latest tool in biologythe microscope.
  • Although Redi had disproved the spontaneous
    generation of large organisms, many scientists
    thought that microorganisms were so numerous and
    widespread that they must arise
    spontaneously-probably from a vital force in the
    air.

4
Spontaneous generation is disproved
  • In the mid-1800s, Louis Pasteur designed an
    experiment that disproved the spontaneous
    generation of microorganisms.
  • Pasteur set up an experiment in which air, but no
    microorganisms, was allowed to contact a broth
    that contained nutrients.
  • Pasteurs experiment showed that microorganisms
    do not simply arise in broth, even in the
    presence of air.
  • From that time on, biogenesis, the idea that
    living organisms come only from other living
    organisms, became a cornerstone of biology.
  • The cell theory states that cells can arise from
    preexisting cells.

5
The Origin of Life
  • Francesco Redi and Louis Pasteur designed
    controlled experiments to disprove spontaneous
    generation.
  • Their experiments and others like them convinced
    scientists to accept biogenesis.
  • But if life comes only from life, then how did
    life on Earth first begin?
  • No one has yet proven scientifically how life on
    Earth began.
  • However, scientists have developed theories about
    the origin of life on Earth from testing
    scientific hypotheses about conditions on early
    Earth.

6
Origins The Modern Ideas
  • Early Earth was hot atmosphere contained
    poisonous gases.
  • Some scientists suggest that it was probably very
    hot. The energy from colliding meteorites could
    have heated its surface, while both the
    compression of minerals and the decay of
    radioactive materials heated its interior.
  • Volcanoes might have frequently spewed lava and
    gases, relieving some of the pressure in Earths
    hot interior. These gases helped form Earths
    early atmosphere. Earths early atmosphere
    probably contained hydrogen cyanide, carbon
    dioxide, carbon monoxide, nitrogen, hydrogen
    sulfide, and water.

7
Origins The Modern Ideas
  • 2. Earth cooled and oceans condensed.
  • About 4.4 billion years ago, Earth might have
    cooled enough for the water in its atmosphere to
    condense. This might have led to millions of
    years of rainstorms with lightningenough rain to
    fill depressions that became Earths oceans.

8
Origins The Modern Ideas
  • 3. Simple organic molecules may have formed in
    the oceans.
  • In the 1930s, a Russian scientist, Alexander
    Oparin, hypothesized that life began in the
    oceans that formed on early Earth.
  • He suggested that energy from the sun, lightning,
    and Earths heat triggered chemical reactions to
    produce small organic molecules from the
    substances present in the atmosphere
  • Then, rain probably washed the molecules into the
    oceans to form what is often called a primordial
    soup.
  • In 1953, two American scientists, Stanley Miller
    and Harold Urey, tested Oparins hypothesis by
    simulating the conditions of early Earth in the
    laboratory

9
Origins The Modern Ideas
  • 4. Small sequences of RNA may have formed and
    replicated.
  • Scientists hypothesize that two developments must
    have preceded the appearance of life on Earth.
  • First, simple organic molecules, or molecules
    that contain carbon, must have formed.
  • Then these molecules must have become organized
    into complex organic molecules such as proteins,
    carbohydrates, and nucleic acids that are
    essential to life.

10
  • 5. First prokaryotes may have formed when RNA or
    DNA was enclosed in microspheres.
  • The first forms of life may have been prokaryotic
    forms that evolved from a protocell. A protocell
    is a large, ordered structure, enclosed by a
    membrane, that carries out some life activities,
    such as growth and division.
  • Because Earths atmosphere lacked oxygen, these
    organisms were most likely anaerobic.
  • For food, the first prokaryotes probably used
    some of the organic molecules in oceans.
  • Over time, these heterotrophs would have used up
    the food supply.
  • However, organisms that could make food had
    probably evolved by the time the food was gone.
  • These first autotrophs were probably similar to
    present-day archaebacteria.
  • Archaebacteria are prokaryotic and live in harsh
    environments, such as deep-sea vents and hot
    springs.
  • The earliest autotrophs probably made glucose by
    chemosynthesis rather than by photosynthesis.
  • In chemosynthesis, autotrophs release the energy
    of inorganic compounds, such as sulfur compounds,
    in their environment to make their food.

11
  • 6. Later prokaryotes were photosynthetic and
    produced oxygen.
  • Photosynthesizing prokaryotes might have been the
    next type of organism to evolve.
  • As the first photosynthetic organisms increased
    in number, the concentration of oxygen in Earths
    atmosphere began to increase.
  • Organisms that could respire aerobically would
    have evolved and thrived.
  • The presence of oxygen in Earths atmosphere
    probably affected life on Earth in another
    important way.
  • 7. An oxygenated atmosphere capped by the ozone
    layer protected Earth.
  • The suns rays would have converted much of the
    oxygen into ozone molecules that would then have
    formed a layer that contained more ozone than the
    rest of the atmosphere.

12
  • 8. First eukaryotes may have been communities of
    prokaryotes.
  • Complex eukaryotic cells probably evolved from
    prokaryotic cells.
  • The endosymbiont theory, proposed by American
    biologist Lynn Margulis explains how eukaryotic
    cells may have arisen. The theory proposes that
    eukaryotes evolved through a symbiotic
    relationship between ancient prokaryotes.
  • New evidence from scientific research supports
    this theory and has shown that chloroplasts and
    mitochondria have their own ribosomes that are
    similar to the ribosomes in prokaryotes.
  • In addition, both chloroplasts and mitochondria
    reproduce independently of the cells that contain
    them.
  • The fact that some modern prokaryotes live in
    close association with eukaryotes also supports
    the theory.

13
Origins The Modern Ideas
  • 9. Sexual reproduction increased genetic
    variability, hastening evolution.
  • increase in genetic variation greatly increases
    the chances of evolutionary change in a species
    due to natural selection
  • 10. Multicellular eukaryotes evolved.
  • cells increased in diversity more rapidly

14
Evolution of Life Review
Evolution of Life
Early Earth was hot atmosphere contained
poisonous gases.
Earth cooled and oceans condensed.
Simple organic molecules may have formed in the
oceans..
Small sequences of RNA may have formed and
replicated.
First prokaryotes may have formed when RNA or DNA
was enclosed in microspheres.
Later prokaryotes were photosynthetic and
produced oxygen.
An oxygenated atmosphere capped by the ozone
layer protected Earth.
First eukaryotes may have been communities of
prokaryotes.
Sexual reproduction increased genetic
variability, hastening evolution.
Multicellular eukaryotes evolved.
15
Patterns of Evolution
  • The history of life is the story of increasing
    complexity and diversity, but what does this
    history reveal about the process of evolution?
  • Biologists have observed different patterns of
    evolution that occur throughout the world in
    different natural environments.
  • Macroevolution refers to the large-scale
    evolutionary changes that take place over long
    periods of time.
  • Six important patterns of macroevolution are
  • mass extinctions
  • adaptive radiation
  • convergent evolution
  • coevolution
  • punctuated equilibrium
  • changes in developmental genes
  • These patterns support the idea that natural
    selection is an important agent for evolution.

16
Mass Extinctions
  • The term used to describe a species that has died
    out is extinct.
  • More than 99 percent of all species that ever
    lived are now extinct.
  • Huge numbers of species have disappeared in mass
    extinctions.
  • The disappearance of so many species left many
    habitats open.
  • For the survivors, there was a new world of
    ecological opportunity.
  • Often, the result was a burst of evolution that
    produced an abundance of new species.

17
Divergent Evolution
  • Divergent evolution occurs when populations
    change as they adapt to different environmental
    conditions, eventually resulting in new species.
    Species that were once similar to an ancestral
    species diverge, or become increasingly distinct.

Possible Ancestral Lasan finch
  • One type of divergent evolution is adaptive
    radiation.
  • Ex Darwins Finches

18
Adaptive Radiation
  • When an ancestral species evolves into an array
    of species to fit a number of diverse habitats,
    the result is called adaptive radiation.
  • Adaptive radiation in both plants and animals has
    occurred and continues to occur throughout the
    world and is common on islands.

19
Coevolution
  • The process by which two species evolve in
    response to changes in each other over time is
    called coevolution.
  • The trees have evolved in response to their seed
    predators, we can observe geographic differences
    in pinecones.
  • Where there are squirrels, the pinecones are
    heavier with fewer seeds, but have thinner
    scales, like the pinecone on the left.
  • Where there are only crossbills, pinecones are
    lighter with more seeds, but have thick scales,
    like the one on the right.
  • The crossbills have evolved in response to the
    pine trees, we can observe geographic differences
    in birds.
  • Where the pinecones have thick scales, birds
    should have deeper, less curved bills (below
    right) than where the pinecones have thin scales
    (below left).

20
Convergent Evolution
  • A pattern of evolution in which distantly related
    organisms evolve similar traits is called
    convergent evolution.
  • Convergent evolution occurs when unrelated
    species occupy similar environments in different
    parts of the world.
  • Each of these animals has a streamlined body and
    various appendages that enable it to move rapidly
    through water. Yet, the shark is a fish, the
    penguin is a bird, and the dolphin is a mammal.
  • They have evolved similar traits because they
    share similar environmental pressures.

21
Gradualism vs. Punctuated Equilibrium
  • Scientists once argued that evolution occurs at a
    slow, steady rate, with small, adaptive changes
    gradually accumulating over time in populations.
  • In 1972, scientists proposed a different
    hypothesis known as punctuated equilibrium, which
    argues that speciation occurs relatively quickly,
    in rapid bursts, with long periods of genetic
    equilibrium in between.
  • Environmental changes, such as higher
    temperatures or the introduction of a competitive
    species, lead to rapid changes in a small
    populations gene pool that is reproductively
    isolated from the main population.
  • Speciation happens quicklyin about 10,000 years
    or less.

22
Gradualism vs. Punctuated Equilibrium
  • Biologists generally agree that both gradualism
    and punctuated equilibrium can result in
    speciation, depending on the circumstances.
  • Gradualism involves a slow, steady change in a
    particular line of descent.
  • Punctuated equilibrium involves stable periods
    interrupted by rapid changes involving many
    different lines of descent.

23
Developmental Genes and Body Plans
  • Hox genes are called master control genes,
    because they control growth as an embryo
    develops.
  • Some hox genes determine which parts become
    front, rear, top, and bottom.
  • Others control the growth of body parts such as
    arms, legs, and wings.
  • The timing of genetic control during embryonic
    development can make the difference between
    various traits.

24
Patterns of Evolution Flow Chart
Species
that are
in
under
under
form
in
in
can undergo
can undergo
can undergo
can undergo
can undergo
Convergent evolution
Punctuated equilibrium
Adaptive radiation
Co evolution
Extinction
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