This document discusses several hypotheses for the origin of life on Earth. It proposes that early conditions allowed for the abiotic synthesis of small organic molecules like amino acids and nucleotides. These molecules could have joined to form polymers like proteins and nucleic acids. Self-replicating molecules then developed that allowed for inheritance. Early life forms may have been encapsulated in membrane-bound droplets called protobionts that could metabolize and replicate. Experiments simulating early Earth conditions provide support, finding amino acid production from organic precursors with energy from lightning or UV radiation. RNA may have played a key role in self-replication before DNA and proteins. Natural selection among primitive self-replicating systems could have driven the evolution of early life.

1. THE ORIGIN OF LIFE
The Evolutionary History of
Biological Diversity

2. Chemical Evolution
Most biologists favored the hypothesis that life on
Earth developed from living materials that became
ordered in to molecular aggregates that were eventually
capable of self-replication and metabolism

3. Biogenesis Paradox
Spontaneous Generation
Life emerging from inanimate materials
Louis Pasteur
Biogenesis
“Life-from-Life”
Reproduction of previous life
Early Earth
Conditions were very different; oxygen, lightning, volcanic activity, sunlight

4. Four Stage Hypothesis
1) Abiotic synthesis of small organic molecules; amino
acids, nucleotides
2) Joining of these molecules into polymers; proteins,
nucleic acids
3) Origin of self-replicating molecules that made
inheritance possible
4) Packaging into Protobionts--droplets with
membranes and an inner chemical composition
different than its surrounding

5. Pasteur and
Biogenesis of
Microorganisms
1) Sterilized Beef Broth,
after few days broth
became spoiled with
microorganisms
2) Sealed sterile broth
remained sterile for
months
3a) Swan-neck flasks
traps dust and
microorganisms,
remained sterile
3b) Broken swan-neck
gave access to
microorganisms; broth
spoiled

6. Abiotic synthesis
Oparin & Heldane independently postulated that early
environments favored abiotic synthesis
Oxygen attacks chemical bonds, extracting electrons
Electron adding atmosphere from volcanic vapors enhanced the joining of
simple molecules
Energy was derived from intense UV radiation and lightning

7. Miller-Urey
#2 Experiment
Atmosphere = H2O, H2,
CH4, and NH3
#1) Warm water
simulated primeval sea
#2) Sparks were
#3 discharged to mimic
lightning
#3) Condenser cooled
water and dissolved
contents went back to
the miniature sea
After one week, the
solution turned from
clear to musky brown,
#1 analysis showed variety of
organic molecules,
including amino acids
and proteins

8. Another Hypothesis
It is also plausible that some organic compounds
reached the Earth from space. Scientists showed how
Adenine could form by the reactions of cyanide in the
clouds of stars. This would explain why some
meteorites carried organic molecules

9. Laboratory Simulations
Link monomers without the help of enzymes
Polymerization by dripping on hot sand, clay, or rock
Water splashing on fresh lava

10. RNA
RNA self-replication
Ribozymes - RNA catalysts
RNA self-replicated when added to organic monomers
Autocatalytic

11. Natural Selection
Single strand = variety of 3D shapes, giving it Genotype
and a Phenotype
Certain base sequences replicate faster and more
accurate
Competition

12. Protobionts
Aggregates of abiotically produced molecules
No precise reproduction
Can maintain an internal chemical environment
different than the surrounding; metabolism and
excitability
Discharge voltage across surface in a nerve-like fashion
Split and produces smaller replicas

13. Natural Selection &
Protobionts
The most successful Protobionts would grow and split
Differential reproductive success of varied individuals
Darwinism