Transcript Early Earth and Theories

Early Earth and
Theories on the Origins of Life!
In your investigation today, you will
explore the early experiments with life
on earth and then create proto-cells in
the laboratory!
Earth History
Earth History:
• Evolution is studied using concepts about earth history. The earth is
between 4.3 and 4.5 billion years old.
• Approximately 3.9 billion years ago, the surface was likely cool enough for
water vapor to condense. (Oceans formed.)
• Many of these events and organisms are recorded on the
geologic time scale.
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As geologists provided evidence
about the age of the earth and the
rate at which changes happened,
biologists began to suspect that life,
and life forms also changed over the
same time.
Geologic and evolutionary change is
a long and slow process.
People wondered, how did life arise?
http://www.youtube.com/watch?v
=QDqskltCixA
First Ideas:
Spontaneous Generation
• Aristotle about 2300 years ago argued that air
provided a vital life force that could produce life
from nonliving substances. This is called
spontaneous generation.
• The idea of spontaneous generation prevailed
for thousands of years.
– What do you think could have been the implication
of this theory on ideas of human reproduction?
• This idea was not formally tested until the
1700s.
Key Scientists – Origin of Life
Francesco Redi (1626-1697)
• First strike against spontaneous
generation, his work:
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Experimental Group: Covered jars with
meat = NO maggots
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Control Group: Meat in uncovered jars
= maggots
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Conclusion: Only flies where there are
maggots AND only maggots where
there had been flies… flies must come
from flies.
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It was concluded and believed they
were a product of spontaneous
generation from a “vital force” or life
force in the air.
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*As the microscope became a widely
used tool for scientists, microorganisms
were seen everywhere.
Remember, around 1678, Anton van
Leeuwenhoek observed “animalcules”
in water. We now know that these
are protozoa.
What do you think people thought this
“vital force” might be?
Key Scientists – Origin of Life
Lazzaro Spallanzani (1729-1799)
Why do you think when presented
with scientific evidence, that society
still clung to the idea of spontaneous
generation?
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Experimental Group: Boiled meat
broth and sealed it in flasks = no
microorganisms
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Control Group: Boiled meat broth,
unsealed flask=microorganisms.
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Conclusion: Only had presence of
microorganisms when they had
access to the broth.
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*His doubters claimed he had killed
the “vital force” in the air when he
boiled the broth and it could then not
generate life.
It was convincing enough to keep the
belief of spontaneous generation
going for another 100 years!
Key Scientists – Origin of Life
Louis Pasteur (1822-1895)
• Experiment: Boiled broth and enclosed it
in an “S” curved neck flask. It was open
and exposed to air, however not directly.
Exposed for 1 year, no microorganisms;
Removed “S” curve and exposed it for 1
day! = microorganisms
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Conclusion: Spontaneous generation was
disproved and biogenesis theory was
substantiated. (Confirmed, make real or
actuated) Contamination came from other
microorganisms, not “air”.
Modern biologists support biogenesis, the
idea that “living organisms only come
from other living organisms.”
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That then brings up the question of how
life began on Planet Earth.
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If Life can only come from life, we know at
some point there had to be a start to
“life”…
– Where would you start looking for
early life?
Key Scientists – Origin of Life
Oparin’s Ideas:
a. Heterotrophs ate the
organic molecules in their
environment until the food
sources were very scarce
b. Organisms needed
another source of energy
c. Autotrophs evolved
(organisms that can make
their own food source)
d. Oxygen became
prevalent in environment
e. Cellular Respiration
possible
f. Eukaryotes evolved
Alexander Oparin (1894-1980)
NO EXPERIMENTS!!
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Earth’s early atmosphere: HCN, CO2,
CO, N, H, S, HOH
1936 - Stated that the earliest living
organisms on earth were simple
heterotrophs (organisms that cannot
make their own food)
Knew these elements (in the form of
various gases) were present in the
earth’s early atmosphere.
When heated (geologic activity) they
might form organic compounds.
Once condensed these compounds
would be in earth’s water bodies.
Oparin: “Life arose from the oceans.”
He believed that energy from lightning
and the sun can spark chemical
reactions to create macromolecules like
proteins.
Formation of Organic Compounds
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Stanley Miller (1930- ) and
Harold Urey (1893-1981)
Miller & Urey’s experiment:
Mixtures of the organic compounds
necessary for life could have arisen from
simpler compounds present on primitive
earth.
• C, H, N, O  all known to exist on earth
since the planet was formed. How did
they turn into the fundamental organic
compounds we know today?
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– Used Oparin’s concept and designed a
contained experiment.
– Lightning with atmospheric gases created
amino acids and eventually life!
1950’s, amino acids heated without oxygen,
they formed AMINO ACIDS !!
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Why is this significant?
Same with ATP and nucleic acids!
Key Scientists – Origin of Life
Sidney Fox (1912- 1998)
• -Studied the development of the first cells; found
structures that have some cell life characteristics.
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Microspheres – microscopic droplet enclosed by a
membrane of organic molecules. (Predominantly
proteins.)
They can form buds, split and take up certain
substances from surroundings.
Sydney Fox produced protocells by heating
solutions of amino acids.
Microspheres
Coacervates – small organic droplet formed by
different types of organic molecules.
They can grow and take up substances from
surroundings. (lipid bi-layer)
NOTE: These are NOT ALIVE  no heredity,
instead of reproduction, they form spontaneously
under proper conditions.
Remember back to the Ecology unit, what are
some of the criteria to be considered living?
What is something else you know of that is not
considered to be alive?
Coacervates
Key Scientists –
Origin of Life
• Lynn Margulis (1938)
• Conducted experiments in the 1960’s
• Evidence:
– 1. Mitochondria and Chloroplast
DNA is similar to bacterial DNA.
– 2. Mitochondria and Chloroplasts
have ribosomes who size and
structure resemble bacteria.
– 3. Mitochondria and Chloroplasts
reproduce by binary fission like
bacteria.
• She determined the endosymbiont
theory that ancient prokaryotes
became the first cellular organelles.
• This is significant because this was
one of the first driving forces of the
theory of evolution!
The Evolution of Cells
• 1st cells were prokaryotic heterotrophs.
Chemosynthetic bacteria came next like
archaebacteria.
• Photosynthetic cells came later and added oxygen
and the ozone to the atmosphere.
• Allowed for eukaryotes because the new ozone
layer protected from UV rays and oxygen allowed
for aerobic respiration.
Origin of Eukaryotic Cells
• Endosymbiont Theory: Eukaryotic
cells arose from living communities
formed by prokaryotic organisms.
• The evolution towards eukaryotic
cells began between 1.5 and 2
billion years ago in what is known
as “endosymbiosis”: an internal,
mutually beneficial relationship.
• Small aerobic prokaryotes are
thought to have entered and lived
inside larger anaerobic
prokaryotes. Later additional
small photosynthetic prokaryotes
are also thought to have entered
and lived inside.
• This is huge! Chloroplasts!!
Mitochondria!!
What is some evidence that you know of
that would lead you to think that
chloroplasts and mitochondria are
unrelated to our genetic history?
Early Life on Earth: What we know
now!
Early Life on Earth:
• It is known that at the beginning there was little to no oxygen available in
the earth’s atmosphere. All living things must have been anaerobic.
• The small size of the microfossils found indicates early organisms were
prokaryotes. Likely these were heterotrophs (does not make their own
food) that ate spontaneously formed organic compounds.
• Supply and Demand: as the supply of
these compounds became scarce, it
became necessary to evolve.
• Became Autotrophs (can make own food).
Early Life on Earth: What we know
now!
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The “archaebacteria” of today are likely similar organisms to those early life
forms.
Archaebacterium – Kingdom of unicellular organisms that live in anaerobic
marine sediments.
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They learned to use chemosynthesis: CO2 is the
carbon source for needed organic molecules,
energy is obtained through chemical oxidation of
inorganic molecules.
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Oxygen, as it became present in the atmosphere was often harmful to early
unicellular organisms, but by 3.5 billion years ago, some life forms had become
photosynthetic and oxygen in the atmosphere increased.
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Evidence of a group similar to the cyanobacteria of today;
Cyanobacteria – (blue green) a group of
photosynthetic unicellular prokaryotes.