Origin of Life
o essential elements that make up the organic compounds: hydrogen,
carbon, nitrogen, oxygen and phosphorous etc. upto iron. Carbon
nitrogen and oxygen produced through nuclear fusion (CNO cycle)
and the others till iron were made from a nuclear fusion in the run.
Others were generated through supernova (very high temperature
explosion) creates heavier elements.
o living organisms need energy to sustain otherwise they would decay.
Need a constant source of energy from the sun which is 6000 K
degrees and emission of electromagnetic energy (heat) is what drives
processes and gives us energy
o water is required for all life forms on earth. 0-100 degrees Celsius
needed for liquid water.
Life cycle of a massive star
o as a while, the inside of the earth is reduced. it s packed with
elemental iron – it can easily donate electrodes
o the further you go out, there is more oxidized elements
o the crust is mostly silicates outer surface from about 3 km beneath
the surface to 30-40 above the earth’s surface contains living
o core: quartz
o mantle: iron magnesium silicate
o stratosphere: felix (jumper experiment) organisms can survive or get
o biosphere: terrestrial and aquatic environment
Evidence for ancient life on Earth
o stromatolites: rocky substances with many microbes growing inside
them and cellular shape can be visualized under the microscope.
Deposit of silicates and calcium carbonate within cells.
o Microfossils: decayed microbial cells with distinct morphology filled
with calcium carbonate/silicate.
o Isotope ratios: analysis of isotopes 12C:13C ratio. S32:S34 also used. If
substances have been processed by biological metabolism, then the
ratio of lighter isotope would be enhanced and heavy isotope would
be reduced. Heavy isotope depletion. Because current metabolic
enzymes have preference for lighter isotopes.
o Biosignatures: sterols are very stable due to rings. If they are
preserved they can last for hundreds of years in rocks. Evidence that
living organisms exist.
o Oxidation state: when it is extremely red, it shows iron has been
oxidized and you can date the banded iron this would indicate banded iron was produced in the presence of oxygen that was
produced by cyanobacteria at that time point. Earth was in a reduced
state (with little oxygen) in the past.
Geological evidence for life on Earth
o oldest sedimentary rocks presence of water. Some have c13
depletion (relatively high ratio of c12 compared to 13) evidence of
o Recent studies show that even though there is 13C depletion,
evidence of microfossil in this rock has been refuted.
o 2.5 billion years ago C13 depletion and hopanoid finding, gradual
increase of O2 concentration in the atmosphere due to finding
o Colonies of bacteria (cyanobacteria) can’t be formed without the
presence of oxygen
o ½ billion years ago complex life forms (multicellular organisms)
o Cambrian explosion 500,000 years ago Rocky Mountains
Canada has evidence
o isotope ratios and potential presence of life
o 12,13C are stable and 14C is not stable because it tends to decay
o Ratio of 12C and 13C would typically be 20:1 or 19:1
o In most objects on earth, 12C would be greater than 19:1 and 20:1
o The more metabolic processes occur, the more enriched 12C will be
o Oxidation/reduction: Lithotrophs can use inorganic electron
donors to harvest energy and oxidize inorganic compounds (they
don’t need oxygen). These were the first things on earth because
there was no oxygen present.
o Light driven proton pumps
bacteriolodoxin* retinol pigment can absorb energy and
generate a proton gradient that can synthesize ATP
combine carbon dioxide and oxygen
Proposed time line
o Archaen: C13 or S34 depletion, some uncertainties about when
oxygen was formed (presence of oxygenic photosynthesis)
o Proterozoic: Cyanobacteria provides robust evidence of oxygen
presence and lead to a lot of life forms
Models for early life
o probiotic soup
inorganic compounds can produce organic compounds
all amino acids and nucleotides can be abiotically synthesized
with the simple input of energy monomers can be synthesized thin atmosphere and no filtration of UV light provided earth
with a lot of energy, there were a lot of inorganic compounds
present this formed a random inorganic soup. Monomers
interacted with each other and formed primitive compounds
like phospholipids which could have proceeded to form cells.
TCA cycle shared among living organisms
carbon dioxide fixation is integral to living organisms need
certain elements for cell maintenance and energy generation
o rna world
nucleotides required for rna purines, pyrimidines and
nucleotides can be synthesized in an abiotic environment
polymerization of nucleotides can happen spontaneously
given enough energy
how can RNA act as an enzyme in catabolizing its own
synthesis and its own splicing, or genetic material template in
replication and transcription?
it is accepted that RNA was most likely the first genetic
most cellular organisms use DNA, why do we have a switch