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The exact origins of life are unclear
We will examine the most plausible
explanations and theories.
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Space programs & imaging
Crust Deposits
Computer Simulations
Fossilized Remains & DNA analysis
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Hubble’s theory of an expanding universe
Redshift and Blueshift Similar to the doppler
effect in sound waves.
15 billion years ago the universe was more
concentrated & exploded sending matter and
energy into space
Gravity caused the matter to clump together
into planets and galaxies.
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Earth’s molten core suggests that Earth began
as a hot mass that lost heat from its surface
creating the surrounding atmosphere of gases
The atmosphere likely arose from volcanic
eruptions and played a role in the origins of
living organisms. (still debated )
Geologic evidence does not support the
presence of O2 in the early atmosphere.
◦ But Why?
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Oxygen was trapped in compounds (water &
carbon dioxide)
Accumulated after early photosynthetic
organisms began to produce it
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Atmosphere was rich in nitrogen and carbon
dioxide
Extreme UV radiation from the Sun created a
hostile environment on Earth
The now protective Ozone layer did not arise
until photosynthetic organisms added O2 to
the atmosphere over millions of years.
◦ Ultraviolent radiation converts O2 into O3
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1. Life originated on some planet of another
star and traveled to Earth through space on a
bicycle. (ET)
2. Life originated by unknown means of Earth
3. Life evolved from nonliving substances
through interaction with the environment.
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What makes a hypothesis testable?
Could we design an experiment to test or
investigate these 3 explanations?
*Let’s examine some hypotheses and
determine their testability*
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Design an experiment to answer a question
you have about the natural world
◦ Design needs to include:
 The question being investigated
 Your hypothesis (“if then statement”)
 Procedures (how would you test it)
 Variables
 Data Collection ( how would you collect
data)
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Life evolved from nonliving substances by
interacting with the natural environment.
Oparin & Haldane: Energy sources caused
atmosphere gases to react and form organic
compounds. Accumulation = “Hot Soup”
Chemical Evolution (Fig. 17.8)
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Chemical reactions continued and
transformations occurred leading to more
organic molecules
Both Oparin and Haldane suggested the
first life forms were heterotrophic
organisms that survived consuming
organic compounds
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3 major steps
There had to be a supply of organic molecules
produced by nonbiological processes
Processes had to polymerize molecules into
Nucleic Acids & Proteins
Other processes had to organize the polymers
into a system that could replicate itself using the
organic materials produced in step 1.
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Synthesized organic compounds using
electricity & chambered apparatus to recreate
Earth’s early atmosphere.
Results:
◦ Small mass of black tar
◦ Water Turned Red (accumulation of
unidentifiable compounds)
◦ Combination of gas molecules forming new
complex molecules
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The liquid contained amino acids
Amino acids are essential for all living
organisms
It was possible cosmic energy reacted
with the gases in Earth’s early
atmosphere to create organic molecules
essential to life
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Examination of meteorite 1969 –found 2
amino acids that do not occur in living
organisms on earth.
Halley’s Comet 1986- contained several
organic compounds including
Formaldehyde
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Replication of the system
DNA molecules are the universal information
molecule. DNA replication requires proteins.
Protein structure is coded in DNA.
SO which came first? Protein or DNA
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The components of RNA can be produced
nonbiologically
◦ Ribose, nitrogen, phosphate
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The components can join spontaneously
Some RNA molecules can catalyze their own
partial replication
This evidence supports the theory that early
polymers could organize into systems with the
ability to replicate themselves using organic
molecules.
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Scientists have not yet found RNA
molecules that can replicate themselves
completely
Laboratories have been able to simulate
Darwinian evolution with RNA molecules
that catalyze specific reactions.
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RNA serves as the catalyst in a chemical
reaction in some single-celled eukaryotes
RNA molecules that act as enzymes are called
Ribozymes
Ribozymes can catalyze changes in other
molecules or act on themselves.
Ribozymes that act on themselves are not
considered true catalysts because they are
changed as a result of the reaction.
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The ability of the RNA molecule to act as a
catalyst depends on its three-dimensional
structure
A double-stranded region at least 3 base
pairs long is needed to stabilize the loops
that give the ribozyme its catalytic structure
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According to NASA’s Exobiology Program
Life = a self-sustained chemical system
that is capable of undergoing Darwinian,
or biological, evolution
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Biological Evolution consists of 3
processes
◦ Self-reproduction
◦ Mutation that can be inherited
◦ Natural Selection
Example organism that undergo these
processes include
◦ Humans, bacteria, lizards
◦ Basically all living organisms on the
Earth
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The oldest know microfossils are of tiny,
single-celled filaments
◦ Found in northwestern Australia
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The discovery of these microfossils provide
evidence that life appeared on Earth much
early than previously thought.
◦ Found in rocks formed almost 3.5 billion years ago
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Carl Woese suggests that the first
microorganisms were methanogens which are
anaerobic bacteria that obtain energy by using
carbon dioxide to oxidize hydrogen.
Methanogens live in extreme conditions
thought to be like those of the early earth
(extremophiles)
They can live near hydrothermal volcanic
vents(hot) or rock wastes from mining (acidic)
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The first microfossils determined to be eukaryotic
are around 2.1 billion years old.
Fossil evidence indicates eukaryotes thrived
around750 million years ago
Endosymbiotic theory: eukaryotes evolved from
the symbiotic relationships among various
prokaryotic organisms
Lynn Margulis hypothesized that mitochondria
and plastids originated as free-living prokaryotes
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Symbiotic relationships among the
prokaryotes may have provided those
organisms with an environmental advantage
compared to the prokaryotes lacking the
symbiotic abilities.
Internal partners are called endosymbionts.
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LO 1.27 Student is able to describe a scientific
hypothesis about the origin of life on Earth
LO 1.28 Student is able to evaluate scientific
questions based on the hypotheses about the
origin of life on Earth
LO 1.29 Student is able to describe reasons
for revisions of scientific hypotheses of the
origin of life on Earth
LO 1.32 Student is able to justify the selection
of geological, physical, and chemical data that
reveal early Earth conditions.