The Origin of Life
Last Class
Got to know each other a little better
Reviewed Lab SafetyIntroduced BiologyReviewed the Scientific Method
Objectives
Determine the difference between spontaneous generation and biogenesis
Look at the 3 experiments set out to determine how life comes to beRediSpallanzaniPasteur
Compare the “Electric Spark” theory and the “Panspermia” Theory
Where does life come from?
Think (1m)Pair (1m)Share (3m)
The Theory of Spontaneous Generaton
Dark Ages Hypothesis: Living Organisms could
develop from non-living materialWas this hypothesis proven, or
disproven?
Redi’s ExperimentFrancesco Redi (17th C)Commonly held belief that flies were
developed spontaneously from rotting meat.
Hypothesis: Meat kept away from flies would remain free of maggotsExperimental group: Covered jar
containing meatControl group: Open jar containing
meat
Redi’s Experiment Cont’dAfter a few days, maggots
swarmed over the meat in the open jars, none in the covered jars
Conclusion: Experiment showed that flies only come from eggs laid by other flies
Spallanzani’s Experiment Lazzaro Spallanzani Around the time of the invention of the microscope
World introduced to microorganismsBelieved to be generated from “Vital Force” in
the air Hypothesis: Microorganisms are formed from
other microorganisms, not the air.Experimental Group: Boiled clear, fresh broth until
flask is filled with steam, sealed by melting neck closed.
Control Group: Boiled broth, flask left open
Spallanzani’s Experiment Cont’d Observations: Broth in the sealed flask remained clear, while
broth in open flask became clouded with microorganisms Conclusions: Boiled broth became contaminated only when
microorganisms from the air enter the flask
But of course, there were critics…
Opponents to Spallanzani claimed that he left the flask too hot, thereby boiling away all the life force in the air…
Enter Louis Pasteur
19th Century French BiologistConsidered the Father of MicrobiologyHypothesis: If he used a curved neck
flask that allowed air inside the flask, but solid particles (such as microorganisms) not able to get in flask, then the broth would remain clear
Louis Pasteur’s Experiment Cont’d Broth boiled in experimental curved neck flask remained clear
for up to a year! As soon as curved neck was broken, flasks became
contaminated within a day! Conclusions: Pasteur reasoned that the contamination was
due to microorganisms in the air, not a “life force”. Beginning of the principle of…
BiogenesisThe theory that living organisms
come only from other living organisms
In Your JournalWrite out a journal/diary entry from the
view point of one of these scientistsWhat are your observations on that day?What are you expecting from these
observations?Why are you undertaking this
experiment?
But where did all of this life come from?
Though there is no sure-fire way of knowing where all of life came from, there are several theories.
We will focus onElectric ShockPanspermia
Electric Shock
Start at the beginning of the formation of Earth (~4.5BYA)A condensed mass of orbiting debris consisting of
an iron/nickel core, rock surface and an atmosphere consisting of Hydrogen- H2
Hydrogen Cyanide- HCNMethane- CH4
Water- H2O
Ammonia- NH3
Electric Shock
Earth cools off enough to a point where water can collect in hollow and low region of the Earth to form oceansOcean water is salty due to leeching of
earth materials into the water over a course of billions of years
Electric Shock
While Oceans are forming, molecules of the atmosphere begin to react with one another
Set forth by lightning, heat and radiationH2, HCN, CH4, H2O, NH3 React together
to form organic subunits of life moleculesSugars (Glucose), Glycerine(fats),
Amino Acids (proteins), Nucleotide Bases (RNA/DNA)
Electric Shock
Miller and Urey (1950s)Designed an experiment using the early
atmospheric molecules, and conditions similar to early earth, to see if these organic molecules could arise.
Resulted in formation of the organic molecules responsible for life!
Electric Shock Organic Life molecules began reacting with one another
E.g. amino acid+ amino acid= Proteins Sugar + Sugar= Polysaccharides
These reactions lead to complex molecules known as nucleoproteinsLike all life they were able to reproduce, mutate,
evolve, and needed an energy supply (Nutrition)
Electric ShockEventually these nucleoproteins became protocells
Developed a mechanism to utilize the suns energy for nutrition- Rise of Photosynthesis (Became the autotrophic cells)
Electric Shock and the Oxygen Revolution
Development of Photosynthesis meant that Oxygen was being expelled into the atmosphere as a waste product1. Oxygen in atmosphere began reacting with
each other in the upper atmosphere forming Ozone (O3)- protects life from radiaton
2. The Heteroptrophic cells were now able to utilize O2 in the atmosphere and get more energy Aerobic Respiration
Recap
Atmospheric Gases
Simple Organic
Compounds
Complex Biological Molecules
Nucleo-proteins
Heterotrophic Protocells
Hetero-trophic cells (Animals)
Autotropic cells (Plants)
Panspermia Life exists throughout the universe, distributed
by meteorites, asteroids, comets, planetoid and even space crafts.
Tiny microorganisms from other worlds may be ejected on impact, and travel to other worlds, planting their “life seed”
Some of the earliest microorganisms on our planet are able to survive the most extreme conditions of cold and radiation (similar to the conditions of outer space)
In your Journal What are your thoughts on the origin of life? Did you prefer the Electric Shock or
Panspermia Hypothesis? Explain Do you have any other theories on how life
may have come to be?
Ch14 Review when finished For Interest, research other origin of life
theories. Feel free to share with class next day