Early Earth and Origin of Life
• Earth’s original organisms are microscopic and
• Life on Earth originated b/w 3.5- 4 billion years ago.
• Earth formed 4.5 billion years ago.
• Evidence of ancient prokaryotes found in rocks called
stromatolites- banded domes of sedimentary rock
similar to layered mats formed today in salt marshes
and some warn ocean lagoons by colonies of bacteria
and cyanobacteria. The layers are sediments that
stick to jelly-like coats of motile microbes, which
continually migrate out of one layer of sediment and
form a new one above, producing the banded pattern
Major episodes in the history of life
• 1. Origin of Earth
• 2. Earth cool enough for crust to solidify
• 3. Origin of life (prokaryotes)
• 4. RNA sequence data shows prokaryotes split into 2 groups: bacteria and
• 5. Production of oxygen by early photosynthetic prokaryotes create
aerobic atmosphere, and organisms must adapt to being aerobic, and
species set to evolve
• 6. Origin of eukaryotes: protists- large, disparate group of unicellular
eukaryotes and some closely related multicellular organisms
• 7. Origin of multicellular organisms: Plant, fungi, and animals. (fungi more
related to animals than plants) in PreCambrian
• 8. Late PreCambrian: oldest animal fossils
• 9. Plants and symbiotic fungi colonize land: Paleozoic
• 10. Extinction of Dinosaurd at end of Mesozoic
• 11. First humans at end of Cenozoic
First organisms were products of chemical evolution in
• 1. The abiotic (nonliving) synthesis and accumulation of small
organic molecules (monomers) such as amino acids and
• 2. Joining of these monomers into polymers (proteins and
• 3. Aggregation of abiotically produced molecules into droplets
(protobionts) that had chemical characteristics different from
• 4. Origin of heredity (before droplet stage)
• In the present atmosphere, oxygen is rich and attach
chemical bonds, extracting electrons. Before oxygen
producing photosynthesis, Earth had a much less
oxidizing atmosphere. Such a reducing (electron
adding) atmosphere would have joined simple
molecules to form complex ones. This requires a lot of
energy, possible provided from lightning, intense UV
radiation, and volcanic vapors from the atmosphere
back then. Today, the oxygen has produced an ozone
layer that prevents UV radiation.
Stanley Miller and Harold Urey
• They tested Oparin-Haldane hypothesis by creating
experiment similar to Earth’s early atmosphere: used an
apparatus where a warm flask of water represented the sea.
The atmosphere had (H20-water, H2-hydrogen, CH4-methane,
and NH3-ammonia). Sparks were discharged in the fake
atmosphere to mimic lightning. A condenser cooled the
atmosphere, raining water and other dissolved compunds
back to the sea. As material circulated through the apparatus,
the solution in flask turns clear murky brown. After one
week, variety of organic compounds including amino acids
that make up proteins of organisms, were found.
• Living cells may have been preceded by protobionts
(abiotically produced molecules)- cannot reproduce, but
maintain internal environment diff. from surroundings and
exhibit some properties similar to life such as metabolism and
• Coacervate (a protobiont) is a stable droplet that tends to self-
assemble when a suspension of macromolecules is shaken.
Hydrophobic macromolecules surround coacervate, which
absorb substrates from enzymes and release products of
reactions catalyzed by the enzymes.
• Protobionts could have formed spontaneously from abiotically produced
• Microspheres made by cooling solutions of proteinoids (polypeptides
created abiotically from amino acids polymerized on hot surfaces).
Microspheres grow by absorbing free proteinoids until they reach unstable
size, and split to form daughter microspheres.
• In aqueous environ., certain lipids self-assemble to form liposomes, which
some grow by engulfing smaller liposomes and then splitting, other times
giving birth” to smaller liposomes.
RNA is first genetic material
• RNA is autocatalytic, and in prebiotic world,
RNA molecules capable of self-replication:
• RNA acts as template for making
polypeptides; and in turn the polypeptides act
as enzymes that aid in the replication of RNA
• Within a membrane, polypeptides aid the
replication of only the template RNA genes.
Were RNA or DNA genes preceded by simpler
• Amino-adenosine triacid ester (AATE) ,
consists of amino adenosine and an ester.
• AATE can catalyze synthesis of another AATE
by acting as a template.
• This has been a slideshow by SUPER-
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