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Early Life – the evidence
•The oldest well dated and well preserved
microsfossils are Apex Chert at Marble Bar,
Western Australia dated at 3.465 billion years.
Layered between volcanic flows which can be dated
very accurately.
•Microorganisms resemble cyanobacteria (bluegreen algae i.e. pond scum)
•Planet was only a few hundred million years old at
the time the Apex chert was formed.
•Implication that as soon as life could arise it did
arise.
Apex Chert Formation
Say hello to your ancestors !!!
If Life needs water where did it come
from?
• Outgassing of
volcanoes
• Bombardment
of Comets (icy
snowballs)
• Oceans =
Comet Juice
Primordial Soup Recipe
• Solid surface
• Water
• Atmosphere of methane (CH4), ammonia
(NH3), water (H2O), hydrogen sulfide (H2S),
Carbon dioxide (CO2) or carbon monoxide (CO),
and phosphate (PO43-).
• “Reducing” atmosphere - No Oxygen !!!!!!
• Lots of volcanism – raw materials / energy
Miller – Urey experiment
• 1953 – Harold Urey and Stanley Miller - University of
Chicago
• Water (H2O), methane (CH4), amonia (NH3), hydrogen
(H2) and carbon monoxide (CO). The chemicals were all
sealed inside a sterile array of glass tubes and flasks
connected in a loop, with one flask half-full of liquid
water and another flask containing a pair of electrodes.
• The liquid water was heated to induce evaporation,
electrical sparks were fired between the electrodes to
simulate lightning.
• Atmosphere was cooled again so that the water could
condense and trickle back into the first flask in a
continuous cycle.
Miller – Urey experiment
What Did they find?
• One week of continuous operation – Dark “glop”
formed in glassware.
• Miller and Urey observed that as much as 10–
15% of the carbon within the system was now in
the form of organic compounds.
• Two percent of the carbon had formed amino
acids with glycine as the most abundant –
detected (5) amino acids originally – reanalysis
with modern equipment detected (22)!!
• Sugars, lipids, and some of the building blocks
for nucleic acids were also formed.
Problems
• UV radiation would dissociate organic
molecules on the surface (no ozone layer).
• Atmosphere may have been different than
original model (controversial)
• Have mechanism for forming building
blocks, but not actual proteins and DNA
Abiogenesis theories
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Hydrothermal vents
Extraterrestrial origins
RNA world hypothesis
Clay Theory
Ice-world Theory
Thermosynthesis
Many other theories
Problem is that there are too many
theories – no scientific consensus.
• Perhaps more than one path for life
to arise ?
The upshot
• All of your molecules with an atomic number
greater than (3) came from the innards of a star.
• Fossil evidence indicates that life arose very
early in the Earth’s history
• Building blocks of life (amino acids) can be
easily synthesized from non organic compounds
(Urey Miller experiment).
• Formation of more complex molecules of life
(DNA, proteins) has not been explained, but not
for a lack of theories.