Transcript Chap 26 Early Earth and the Origin of Life

Chap 26
Early Earth and the Origin
of Life
Hypotheses for Origin of Life on
Earth
• Divine origin
• Extraterrestrial Origin
• Abiotic Origin
Earth is part of
the _______ __
Galaxy
The components
for life are found
in space.
Eg. Amino acids
.475
.7
1.7
2
3.5
3.8
4
• Alternatively, we
can view these
episodes with a
clock analogy.
Fig. 26.2
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Where did the first cell come
from?
Could life come from non-life?
Spontaneous Generation of Life
Abiogenesis
• In 1862, Louis
Pasteur
conducted broth
experiments that
rejected the idea
of spontaneous
generation even
for microbes.
• A sterile broth
would “spoil”
only if
microorganisms
could invade
from the
environment.
Cells must come from
pre-existing cells
BIOGENESIS
Fig. 26.9
P 494
Ancient Reducing Atmosphere
• Oparin and Haldane proposed that Earth’s
ancient atmosphere was reducing rather
than oxidizing –providing an environment
where Abiogenesis could take place.
• Why was there no free oxygen in Earth’s
early atmosphere?
• Why would the first life not evolve in an
oxidizing atmosphere?
Miller and Urey simulated
Earth’s early atmosphere
electricity simulated lightning
Why should they have used uV
light?
An alternate atmosphere
contained carbon monoxide,
carbon dioxide, nitrogen gas
and water vapor
Experiments have
produce all 20 amino
acids, sugars, lipids,
purines, pyrimidines
What is the importance of
amino acids?
What is the importance of
nucleic acids?
Lightning and uV light provided energy for polymerization
Chemical Evolution
Abiogenesis
•
•
•
•
•
Proposed by Oparin and Haldane
The abiotic synthesis of monomers
Polymerization of monomers
Aggregation of molecules into protobionts
Origin of heredity
Lightning and uV light
provided energy for
the formation of larger
molecules and
polymerization
Adenine is an
important
percursosr
P 495
Polymerization
• When monomers dripped on to hot sand,
clay or rock polymerization can occur
• Clay concentrates amino acids and other
monomers. Its charged surface can act as
catalytic sites for polymerization.
• Pyrite can also act as catalytic sites for
polymerization
Polymerization led to proteins and nucleic acids such as RNA
• Liposomes behave dynamically, growing by
engulfing smaller liposomes or “giving birth”
to smaller liposomes.
Fig. 26.12a
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• If enzymes are included among the
ingredients, they are incorporated into the
droplets.
• The protobionts are
then able to absorb
substrates from
their surroundings
and release the
products of the
reactions catalyzed
by the enzymes.
Fig. 26.12b
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Protobiont Examples
• Coacervate (Oparin)
made of polypeptides
nucleic acids and
polysaccharides
• Proteinoid
Micorspheres (Fox)
• Liposomes
Protobionts
• Aggregates of molecules that:
• can start maintain a different internal environment
(homeostasis)
• can show rudimentary metabolism (catalytic
reactions and modifications)
• can show excitability (membrane potential)
• can reproduce themselves
• maintain genetic material
RNA could not only
replicate itself, but it could
also act as a catalyst
eg. Making proteins
RNA with the best
autocatalytic activity would
predominate
RNA - First Genetic Molecule
6. Natural section could refine
protobionts containing hereditary
information
• Once primitive RNA genes
and their polypeptide
products were packaged
within a membrane, the
protobionts could have
evolved as units.
• Molecular cooperation could
be refined because favorable
components
were concentrated
together, rather than
spread throughout the
Fig. 26.13
2. Prokaryotes dominated evolutionary
history from 3.5 to 2.0 billion years ago
• Prokaryotes dominated evolutionary history
from about 3.5 to 2.0 billion years ago.
• supports the hypothesis that the earliest
organisms were prokaryotes.
• Relatively early, prokaryotes diverged into two
main evolutionary branches, the bacteria and
the archaea.
– Representatives from both groups thrive in various
environments today.
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Oldest fossil is
of a bacteria 3.5
Billion years old
What are
stramatolites?
• Two rich sources for early prokaryote fossils
are stromatolites (fossilized layered microbial
mats) and sediments from ancient
hydrothermal vent habitats.
– This indicates that the metabolism of prokaryotes
was already diverse over 3 billion years ago.
Fig. 26.4
3. Oxygen began accumulating in the
atmosphere about 2.7 billion years ago
• Photosynthesis probably evolved very early in
prokaryotic history.
– The metabolism of early versions of
photosynthesis did not split water and liberate
oxygen.
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• Cyanobacteria, photosynthetic
organisms that split water and
produce O2 as a byproduct,
evolved over 2.7 billion years
ago.
– This early oxygen initially reacted
with dissolved iron to form the
precipitate iron oxide.
• This can be seen today in banded iron
formations.
– About 2.7 billion years ago oxygen
began accumulating in the
atmosphere and terrestrial rocks
with iron began oxidizing.
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• While oxygen accumulation was gradual
between 2.7 and 2.2 billion years ago, it shot
up to 10% of current values shortly afterward.
• This “corrosive” O2 had an enormous impact
on life, dooming many prokaryote groups.
– Some species survived in habitats that remained
anaerobic.
• Other species evolved mechanisms to use O2
in cellular respiration, which uses oxygen to
help harvest the energy stored in organic
molecules.
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4. Eukaryotic life began by 2.1
billion years ago
• Eukaryotic cells are generally larger and more
complex than prokaryotic cells.
• In part, this is due to the apparent presence of
the descendents of “endosymbiotic
prokaryotes” that evolved into mitochondria
and chloroplasts.
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• While there is some evidence of earlier
eukaryotic fossils, the first clear eukaryote
appeared about 2.1 billion years ago.
– Other evidence places the origin of eukaryotes to as
early as 2.7 billion years ago.
• This places the earliest eukaryotes at the same
time as the oxygen revolution that changed the
Earth’s environment so dramatically.
– The evolution of chloroplasts may be part of the
explanation for this temporal correlation.
– Another eukaryotic organelle, the mitochondrion,
turned the accumulating O2 to metabolic advantage
through cellular respiration.
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Endosymbiotic Theory
Section 17-2
Chloroplast
Aerobic
bacteria
Ancient Prokaryotes
Nuclear
envelope
evolving
Plants and
plantlike
protists
Photosynthetic
bacteria
Mitochondrion
Primitive Photosynthetic
Eukaryote
Ancient Anaerobic
Prokaryote
Primitive Aerobic
Eukaryote
Animals, fungi, and
non-plantlike protists
Mitochondria and Chloroplasts are thought to have been engulfed by
Archaea Bacteria and formed the first eukaryotic cells - 3 bya
5. Multicellular eukaryotes
evolved by 1.2 billion years ago
• A great range of eukaryotic unicellular forms
evolved into the diversity of present-day
“protists.”
• Multicellular organisms,
differentiating from a
single-celled precursor,
appear 1.2 billion years
ago as fossils, or perhaps
as early as 1.5 billion
years ago from molecular
clock estimates.
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Fig. 26.6
• Recent fossils finds from China have produced
a diversity of algae and animals from 570
million years ago, including beautifully
preserved embryos.
Fig. 26.7
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6. Animal diversity exploded during the
early Cambrian period
543 to 490 Million Years Ago
• A second radiation of eukaryotic forms
produced most of the major groups of animals
during the early Cambrian period (after ice
age).
• Cnidarians (the plylum that includes jellies)
and poriferans (sponges) were already present
in the late Precambrian.
7. Plants, fungi, and animals colonized
the land about 500 million years ago
• The colonization of land was one of the pivotal
milestones in the history of life.
– There is fossil evidence that cyanobacteria and
other photosynthetic prokaryotes coated damp
terrestrial surfaces well over a billion years ago.
– However, macroscopic life in the form of plants,
fungi, and animals did not colonize land until
about 500 million years ago, during the early
Paleozoic era.
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Old
5 Kingdom
Classification
system lumped
all prokaryotic
organisms into
Monera
Protista was found to be polyphyletic which led
to it become broken up into smaller kingdoms
Two distinct lines of Prokaryotes leads
to the Three Domain system.