Chapter 19-1 ~ Origin and History
of Life
Close your eyes and
imagine our
planet 4 billion
years ago… what
do you see? How
is it different from
today?
Early history of life









Solar system~ 12-10 billion
years ago (bya)
Earth~ 4.6 bya
Life~ 3.5 to 4.0 bya
Prokaryotes~ 3.5 to 2.0 bya
stromatolites
Oxygen accumulation~ 2.7 bya
photosynthetic cyanobacteria
Eukaryotic life~ 2.1 bya
Muticelluar eukaryotes~ 1.2 bya
Animal diversity~ 543 mya
Land colonization~ 500 mya
Interesting facts about the origins of life




There is more metabolic diversity among the two
kingdoms of prokaryotes then all the eukaryotes
combined
Bacteria separated from Achaea bacteria early on
in the history of life ~2 to 3 B.Y.A.
Fungi are more closely related to animals than
they are to plants
Fungi and plants worked together to symbiotically
colonize land… which happened fairly recently on
the geologic time scale…. 475 million years ago
Evidence of early life

Stromatolites
are fossilized
layers of
sediment
formed from
the migration
of bacteria
upward
Early fossils
The Origin of Life






Spontaneous generation
vs. biogenesis (Pasteur)
The 4-stage Origin of life
Hypothesis:
1- Abiotic synthesis of
organic monomers
2- Polymer formation
3- Origin of Selfreplicating molecules
4- Molecule packaging
(“protobionts”)
Origin of Life
Organic monomers/polymer synthesis


Abiotic Synthesis Model Oparin /Haldane (1920)
working independently hypothesized that simple
monomers (monosaccharides, amino acids, and
nucleotides) could be synthesized from inorganic
molecules in the early atmosphere in the presence
of volcanic vapors (reducing atmosphere) with
lightning , UV radiation and no Oxygen.
Early atmosphere probably consisted of Water
vapor, N2, and CO2 with small amounts of
hydrogen gas (H2), methane (CH4), ammonia
(NH3), hydrogen sulfide (H2S) and carbon
monoxide (CO).
Testing the abiotic synthesis
hypothesis



Miller/Urey (1953) experiment:
Placed a mixture resembling a strongly reducing
atmosphere of water , hydrogen gas (H2), methane
(CH4), and ammonia (NH3)… heated it and circulated
it past an electric spark for a week.
Results: A variety of amino acids, nitrogen bases, &
ATP formed
Criticism of the Miller/Urey experiment



Placed ammonia (NH3) in the mixture… not a major
component of the early atmosphere… (N2) was
plentiful but inert unlike ammonia
Where was ammonia being synthesized in large
amounts on primitive earth?
Oparin /Haldane hypothesis was modified to include
iron-nickel sulfides produced in the extreme heat of
hydrothermal vents that act as catalysts for froming
both ammonia, amino acids, and even peptide chains!
Polymers Evolve



Fox amino acids can polymerize forming
proteinoids, small polypeptides with some catalytic
capabilities, from organic monomers dripped on hot
sand, clay or rock. Fox also demonstrated in
laboratory the formation of microspheres, small cell
like structure consisting only of protein, from the
coagulation of proteinoids.
Fox proposed the “Protein First Hypothesis” and
stated that protein enzymes came before the genes
that code for proteins.
This is supported also by the fact that DNA
replication is highly dependent upon many protein
enzymes.
Polymers Evolve


Cairns-Smith Polypeptides and RNA Nucleotides
came to be at the same time on a warm bed of clay
that consisted of iron and zinc catalysts. CairnsSmith envisioned the RNA directing the
polypeptides to replicate more RNA which would
code for more polypeptides.
Cech/Altman RNA first hypothesis… RNA was both
the substrate and the enzyme (acting like a
polypeptide/protein) creating a world in which all
the genes were RNA and not DNA.
Protocells or Protobionts…not quite
a cell but it is a start… It has a
membrane
A simple heterotrophic protocell
could have contained RNA
acting as a gene and an
enzyme…Some simple form of
Glycolysis may have been
occurring to produce an ATP
like molecule for energy
Provides a safe place for chemical reactions to occur!
RNA the Origin of Life
Evolution of the Cell
The origin of heredity information
made Darwinian evolution possible


Once a membrane formed around the RNA
that was producing protein, now there was a
selective advantage and the inheritance was
possible
RNA eventually gave way to the more
stable DNA… the “RNA World” gave way
to the “DNA World”!
Panspermia



The idea that Earth was
seeded from life from
outer space
Amino acids are found
in some meteors that
strike our planet today
Early Earth was
bombarded constantly
with meteors
Is life restricted to Earth… What is
your opinion?