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Transcript
Chapter 15
Early Earth and the Origin of Life
Life on Earth originated between 3.5
and 4.0 billion years ago.
The Earth formed about 4.5 billion
years ago.
The first organisms were prokaryotes.
Evidence of ancient prokaryotic life has
been found in rocks called
stromatolites- banded domes of
sedimentary rock
Pre-Cambrian
stromatolites in the
Siyeh Formation,
Glacier National
Park
About 3 billion years ago, the prokaryotes
split into two distinct groups:
Bacteria
Archea
2.5 billion years ago, the production of
oxygen by photosynthetic prokaryotes
created an aerobic atmosphere
Oldest fossils that are definitely
eukaryotic are 1.7 billion years old
Eukaryotes probably evolved from a
symbiotic relationship between
prokaryotes.
Endosymbiosis
://highered.mcgrawhill.com/sites/9834092339/student_view0/chapter4/animat
ion_-_endosymbiosis.html
Those eukaryotic cells evolved into the
ancestors of modern protists, fungi,
plants and animals.
Oldest animal fossils date back to 700
million years ago.
The first cells
The early Earth’s atmosphere consisted
of very little oxygen.
There was a lot of lightning, volcanic
activity, and ultraviolet radiation.
Chemical Evolution
1. Abiotic synthesis of small organic
molecules such as amino acids and
nucleotides.
a. 1920’s - Oparin and Haldane
independently hypothesized that the
reactions that took place on the early Earth
could create organic molecules.
b. This cannot happen today due to the
electronegative nature of oxygen.
c. Early atmosphere- much more reducing
(electron adding)
d. 1953-Miller & Urey- simulated conditions of
the early Earth
e. Experiment produced a variety of amino
acids, sugars, lipids, nucleotides and ATP.
Stanley Miller
2. Joining of monomers into polymers
such as protein and nucleic acids.
a. How would this occur without
enzymes?
b. In experiments, polymerization does
occur when solutions of monomers are
dropped onto hot sand, clay or rock.
 In 1957 Sidney Fox
demonstrated that dry
mixtures of amino acids could
be encouraged to polymerize
upon exposure to moderate
heat. When the resulting
polypeptides, or proteinoids,
were dissolved in hot water
and the solution allowed to
cool, they formed small
spherical shells about 2 μm in
diameter—microspheres.
3. Aggregation of abiotically produced
molecules in droplets called
protobionts.
a. Maintain an internal environment
different from their surroundings.
b. Exhibit some properties associated with
life- metabolism and excitability
c. Coacervates - self-assemble when a
suspension of macromolecules is shaken
d. Microspheres- polypeptides with a
semipermeable protein membrane
1. Undergo shrinking and swelling due to
osmosis
2. Store energy in the form of membrane
potential.
e. Liposomes- form spontaneously
when the organic molecules include
lipids
1. Form lipid bilayer membrane
2. Grow by engulfing other liposomes and
may split to form two
Protobionts
4. Origin of heredity
a. RNA was probably the first genetic material
b. RNA appears to have the ability to selfreplicate short sequences (5-10 bp)
c. RNA may act as an enzyme = ribozymes
d. Once RNA became enclosed in
membranes, these protobionts would
have a form of heredity.
e. These protobionts may be selected
for survival.
f. RNA may have directed the
sequencing of amino acids to form
primitive enzymes.
Debate about the origin of life
A. Scientific evidence for what could
have happened.
B. Alternative scientific theories:
1. Panspermia- meteorites brought
organic molecules formed in outer space.
2. Nucleic acid genes may have been
preceded by simpler hereditary systems.