Download Option D: Evolution

Evolution
Origin of Life on Earth
Dates to Know:

Earth Formed- 4.6
billion years ago

Life began- approx
4.5 billion years ago
Geologic
Time
Scale
Conditions of Pre-Biotic Earth
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Pre-biotic = Before life
existed on Earth
Conditions:
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High temperature
Lightning
UV light penetration
Atmosphere of methane,
ammonia, hydrogen.
Four processes needed for the
spontaneous origin of life on Earth
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The non-living synthesis of
simple organic molecules
The assembly of these
molecules into polymers
The origin of self-replicating
molecules that made
inheritance possible
The packaging of these
molecules into membranes
with an internal chemistry
different from their
surroundings.
The experiments of Miller and Urey

Purpose- to test the hypothesis
that organic molecules can form
spontaneously under the right
conditions.

Gases used: ammonia, methane
and hydrogen, which simulated
the early Earth’s environment.

Set up in a closed system
conditions similar to those of
pre-biotic Earth.
Experimental setup
Miller/Urey Result

It worked! Amino acids and
other simple organic molecules
were formed by the apparatus.

Further confirmation- in 1970 a
meteorite was found to contain
7 amino acids, two of which
are not found in living things
on Earth.

Comets may have delivered
organic compounds to Earth!
Where could organic compounds
have been located?

Deep sea thermal vents

Volcanoes
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Extraterrestrial locations
So…how did life actually begin?

One of the first
properties of ‘life’ is
the ability to
replicate.

One organic
molecule is
naturally set up to
do this…
RNA

Possible scenario involves randomly
created monomers organizing into
polymers which can then self-replicate
Hypothesis that the first catalysts responsible
for polymerization reactions were clay minerals
and RNA.

Clay contains Zinc and other
substances which help it act
like a template, facilitating
the replication of RNA. The
theory proposes that without
clay, 5- chain polymer could
replicate, whereas with clay,
up to 20 chain polymer could
replicate.
Clay!
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1. Some clays can grow by attracting molecules
to themselves-then repeat a lattice-like
organization over and over again.
2. Amino Acids (AA) may have stuck to the clay
lattice and been incorporated into it
Clay may have been a template for a protein
Protein= weak enzymes= speeds up protein
synthesis
More and more templates to more and more
proteins
Eventually RNA makes DNA

Unclear how this occurs- but it still occurs in some
viruses so it is known to actually happen!!
RNA as the first molecule capable of
replicating.

RNA is composed of a
single helix, versus DNA’s
double helix. The bases
are exposed and ready to
combine with a
complement, making
replication simpler that with
DNA, which first requires a
separation of the two
strands.
The First Cells were Prokaryotes
Contribution of prokaryotes to the creation
of an oxygen-rich atmosphere.

Cyanobacteria, which
are photosynthetic,
converted the Earth’s
early atmosphere from
anoxia to one which
contained free oxygen.
This occurred
approximately 2.7 to
2.2 billion years ago.
Courtesy of Ralf Wagner
Origin of Eukaryotic Cells

Endosymbiotic theory- Lynn
Margulis
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Mitochondria were originally
independent organisms, which
were engulfed by another
prokaryotic cell without a cell
wall. Instead of being
destroyed, it thrived inside and
benefited the host. The
relationship eventually became
permanent.

Same thing for chloroplasts.
Endosymbiosis: Eukaryotic cell
evolution

Mitochondria and chloroplasts were once
free living bacteria cells
Mitochondria aerobic bacteria
 Chloroplasts photosynthetic bacteria

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These cells were “swallowed up” by other
cells by endocytosis cells engulfed
but not eaten.
Benefits of Endosymbiosis
Mitochondria additional energy (aerobic
respiration) and receives protection
 Chloroplast provide food by
photosynthesis and receives protection

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Some debate whether endosymbiosis is
really an equal benefit to both cells.
Evidence for endosymbiosis

Prokaryotes are similar to mitochondria
and choloroplasts
Similar size
 Similar ribosomes
 Replicate the same way(mitochondria and
chloroplasts replicate on their own)
 Mitochondria and chloroplasts have their own
DNA, structurally similar to prokaryotic DNA
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Spontaneous Generation

Spontaneous generation: the theory that
living organisms could come from nonliving matter ( special creation – coming
from God)
Ex: flies from rotting meat, snakes and frogs
in mud etc.
 Existed in belief until the mid 1800’s.
 Disproved by Redi and Pasteur experiments.
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Francesco Redi- 1668
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The belief was that maggots “appeared” in meat
Redi set up 2 flasks with meat, one covered and
one uncovered.
The uncovered meat developed maggots after
flies landed on them.
The covered meat did not develop maggots.
Louis Pasteur- 1859
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Set up flasks with broth
in a straight and curved
tube.
When boiled, no
bacteria grew in the
curved flask. In the
open flask, bacteria
grew after sitting for a
few days.
What did these prove?
These experiments proved that life could
not just “appear.”
 Life had to come from other life.
 Thus, spontaneous generation was
disproved.
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