The Origins of Life by DanaG

VIEWS: 1,217 PAGES: 39

									  The facts……. hidden somewhere
      The story….….. unrevealed
    The truth….. not known exactly
         The path…. untraced
   An attempt to explore the way!!!
 An effort to blend biology, chemistry,
and physics in the search to identify and
  understand the origin of life in the
 It’s a “Journey Back In Time”…
         By Kalpana Stuti, Ritu, Gauri
               Miranda House
              BIG BANG

  Cosmic dust and gases+ H2O


           Haldane soup

Reducing atmosphere(gases like
CH4,NH3,N2,CO2,H2O responsible for
abiotic synthesis of organic compounds)
                   Haldane Soup

                 Simple Molecules

        Complex Molecules (building blocks)

    Aggregates (coacervates and microspheres)              Microsphere

Protocells( proprimitive stage before formation of true cell

    Proto cells + nucleic acid = self replicating system

 • ―Cell‖                      Energy Yielding System

 • Chlorophyll   development         Photosynthesis

                                     O2 evolved

                    Ozone Formation (shielding effect)

• Atmosphere     changed to oxidizing from reducing.
• Evolutionof photosynthesis which is followed by

  Replication   Metabolism                 Homeostasis

    Anaerobes                              Aerobes
  Chemotrophs                          Heterotrophs

Chemoheterotrophs                          Chemoautotrophs
Prokaryotic Cells                           Eukaryotic cell
                    Endosymbiotic Theory
How Eukaryotic Cell Changed to
  Multicellular Organism….

• Geological Evidence

• Precambrian Fossil Evidence

• Laboratory Evidence
• Sedimentary rock in past 500 million years are
  silicate sands clay, quartz type indicating oxidizing

• Ancient Precambrian sediments containing sands with
  reduced iron minerals found in Canada, Brazil, South

• Banded iron ore deposits with mixed oxidation states
  in Quinland, Russia, India and Australia
• Elso Barghoorn et al studied polished thin sections
  of silica rich cherts from Gunflint region of
  Northern Minnesota and Southern Canada with
  optical and electron microscope.

• Living organisms algae, fungi, microbes associated
  with banded iron ore cherts indicates that they
  were probably laid down under reducing
  atmospheric conditions.
                 MILLER & UREY EXPERIMENT
•A mixture of H4,NH3, H2, and water
was put into a flask and energized
by an electrical discharge apparatus
to represent ultraviolet radiation .
•The products were allowed to
condense and collect in a lower flask.
•. After a week, Miller and Urey
found a dark brown scum had
collected in the lower flask and was
found to contain several types of
amino acids together with sugars,
tars, and various other unidentified
organic chemicals.
 How could polymer form in dilute aqueous
 solution when polymerization is a dehydration
• Sidney Fox experiment – Fox found that dry amino
  acids heated to 160-210OC, forms polymers of molecular
  weight 300,000 provided mixture contains Aspartic Acid
  and Glutamic Acid. Thermal protenoids so formed, if
  washed with water, form microspheres of fairly uniform
  diameter of 20, 000Ao

• Cinder Cone Hypothesis - Protenoid material first
  polymerized on hot dry volcanic Cinder Cones and then it
  was leached into oceans by rains to form microspheres.
These became early segregated chemical systems and
  eventually led to protocells.
• They tend to concentrate
  some molecules in their
  interior and this in an ability
  that most primitive protocells
  would have acquired.
  Behavior of Coacervate shows
  how earlier protocells would
  have achieved internal
  compositions that were
                                    Coacervate droplets formed
  different from their              by interaction between
  surroundings and could have       gelatin and gum arabic. A. I.
  developed certain amount of
  chemical evidences.
 Starch       Amylase       Maltose

             Chloroplast   Reduced Dye
              e- + Dye     (colour change)
Acid + Dye
Organic compounds arrived from outer space
It states that hydrocarbons and other organic
molecules (molecules that organisms contain or that
might lead to the genesis of life) have been found in
meteorites –
 It means that at least prebiotic chemistry that leads
to the primordial soup might be going on there.
 Evidences in support of this theory
• In 1969, a meteorite landed in Australia that was 12%
  water and contained traces of 92 amino acids.
  Inference- It points to not only the presence of
  organic compounds in outer space, but also the
  capacity of such compounds to reach earth.

• Fred Hoyle and Chandra Wickramasinghe have
  argued persistently since the 1970s that complex
  organic substances, and perhaps even primitive
  organisms, might have evolved on the surface of
  comic dust grains in space and then been transported
  to the Earth's surface by comets and meteorites.
             Where did life begin???
• There is an ongoing debate regarding the most probable site of
  life's origins.

• The prevailing paradigm - life began near the ocean's surface,
  bathed in sunlight.

• Current Research - life Miller and Urey foundhydrothermal vents
                           arose near deep
  which is still under investigation.

"Scientists have long suspected that life on Earth originated in the
  ocean and strong evidence now suggests that the earliest life on our
  planet occurred in the depths of the ocean in the absence of heat
  and light."

-- Pulse of the Planet, American Museum of Natural History
Photograph from National Geographic magazine
            Deep-sea Vents
• Their discovery in late 1970’s stretched our
  concept of the origin of life on earth.
• Can life exist and that too thousands of
  meters beneath the surface of sea in absence
  of sunlight?
• It raised the possibility that earlier vents
  supplied the energy and chemical
  precursors for origin of protobionts.
      Exploring the deep ocean floor
 View of the first high-
   temperature vent
 (380°C) ever seen by
scientists during a dive
    of the deep-sea
 submersible Alvin in
Such geothermal vents
  are called smokers.
                           This photograph shows a black smoker, but
                            smokers can also be white, grey, or clear
                            depending on the material being ejected.
                            Photograph by Dudley Foster from RISE
                  Vent Community

A vent community in its prime: Pale pink eelpout fish and white
 brachyuran crabs swim and scuttle among blood-red tube worms
   large and small. Scientists are still trying to figure out how the
     offspring of such organisms disperse over long stretches of
  inhospitable seafloor to colonize widely separated vent systems.
               Giant Clams

The size of deep-sea giant clams is evident from the
         hands of a scientist holding them.
  (Photograph by William R. Normark, USGS.)
        Giant Tube Worms: RIFTIA
• On the bottom of
  the ocean around
  hydrothermal vents,
  there is a profusion
  of life that thrives
  on the hydrogen
  sulfide (H2S) gas
  released from the
  vents.and live inside
  hard, shell-like        Giant tubeworms that live around hydrothermal vents
                          on the sea floor. These creatures are about the size of
  protective tubes that   your hand in shallower waters, but in the ocean's deep
  attach to the rocks.       they have been found as big as eight feet long!
                   How they live….
• These creatures lack mouths, anuses, intestines and stomachs,
  and scientists were at a loss to explain how these were getting
  nutrients to survive and grow.

• Their insides are lined with bacteria that oxidize the H2S,
  turning it into usable nutrients for the worms.

• The bacteria, in turn, benefit from the relationship because the
  worms deliver blood containing hemoglobin which helps the
  bacteria to break down the sulfides.

• They live in a symbiotic relationship with a bacteria that may
  hold clues as to how life on earth began billions of years ago.
                              Energy released helps in fixing
• H2S          Oxidation by
                 bacteria     CO2 into small organic molecules
  from vents

So this cycle ... is the same metabolic pathway that is utilized by
plants in photosynthesis ... takes inorganic carbon dioxide and
fixes it into organic compounds that are then food. But, the
difference here, the critical difference, is that rather than using
sunlight, these animals and bacteria are completely independent of
sunlight. They utilize chemical energy to power that reaction.

So, ever imagined a life out of toxic Hydrogen Sulphide?!
    Chemical of Life - Ammonia,
        Produced at Vents
• Hydrothermal vents were the most likely site for
  NH3 production where inorganic sulphides acted
  as catalyst.
                   N2 +NO2 +N03
                   Presumed to be present
                       in ancient sea
46% yield 15 min           FeS, 500oC
                                               20% yield
                           89% yield, 15 min

                     Stable upto 800oC
• Since NH3 cannot survive at temperature above
  800oC indicates that nitrogen would have been
  present only as N2 during early phase of earth’s

• Life can exist on thermal and chemical energy as
  opposed to just sunlight as had been thought in the
  past. And so what was realized is that photosynthesis
  was not the only way to support life.
        THE BIG BANG
First proposed by George Lemaître in 1927
          Salient Features
 •Our Universe began as an
 infinitesimally small, infinitely hot,
 infinitely dense singularity.

 •Then it inflated (big bang), expanded
 and cooled to the size and temperature
 of our present Universe.
Timeline of the Big Bang
            What happened after the
                  Big Bang?
Time since           T
Big Bang             (K)
 < 10-43s                    Quantum era

 ~ 10-35s - 10-33s           Inflationary epoch

~ 10-6s              1013K   Quark --> Hadron transition
Time since   T
Big Bang     (K)
 0.01s       1011K      · The Universe expands rapidly,
                        scale is doubled every 0.02s.
                        · it cools, T ~ 1/R.

15s          3 x 109K   · Temperature is below threshold
                        for creation of electron/positron
                        · e+/ e- annihilate
                        · The Universe is "reheated"
                        about 35% by annihilation.
 3 min       109K       Era of Nuclear Reactions
                        · Nuclei begin to hold together
Time since   T
Big Bang     (K)

3 &1/2 min   108K           End of Nuclear Reactions
                            neutrons have been "used-up"
                            forming 4He
                            Universe is now 90% H nuclei( p+)
                            & 10% He nuclei

106yr               4000K   Era of Recombination
                            nuclei & electrons "recombine to
                            form atoms

109yr                       Era of Galaxy Formation
   Evidences for the Big Bang
•Galaxies are moving away from us at speeds
proportional to their distance. This is called
"Hubble's Law," named after Edwin Hubble
(1889-1953) who discovered this phenomenon in
•The abundance of the "light elements" Hydrogen
and Helium found in the observable universe are
thought to support the Big Bang model of origins
•Cosmic Background Radiation predicted by
Cosmologist George Gamov in 1948 and discovered
by Arno Penzias & Robert Wilson of Bell Labs in
• The Bubble Universe / Andre Linde's Self
  Creating Universe
• The Inflationary Theory (1981, Alan Guth )
• The Protouniverse (white hole theory)
• The Steady State Theory (late 1940’s )
• The Oscillating Universe Theory (1960’s -
  70’s )
• The Cosmos by Carl Sagan
• Text Book of Biology by Campbell
• The Scientific American
• Humphris, Susan E. and Tom McCollom. ―The Cauldron
  Beneath the Seafloor,‖ Oceanus, Vol. 41, No. 2, 1998, 18.
• Sawyer, Kathy. ―Signs of Earliest Life in Ocean Depths—
  Scalding Habitat May Have Supported Microbes, Fossils
  Indicate,‖ Washington Post, June 8, 2000.
  Nobody understands the origin of life. If
they say they do, they are probably trying to
                  fool you.

           — Ken Nealson, 2002

          THANK YOU

To top