1. Chemical Evolution
Proposes life began with the formation of a self-replicating molecule
Origin-of-life researchers are testing the steps of the theory by simulating conditions found in atmosphere and ocean of the early Earth

2. Miller’s experiments
Start with simple molecules like CH4, NH3, CO2 and CO
In the presence of ultraviolet radiation or lightning, these simple molecules can form more complex organic molecules like H2C0 and HCN
The results suggest these nonspontaneous reactions could have occurred on ancient Earth

3. Figure 3.1 Electrode Large glass flask Glass tubing Spark discharge
Stopcock
for taking
samples
Gases
Condenser
Figure: 3.1
Caption:
This schematic diagram shows the important elements in Stanley Miller’s apparatus for conducting spark-discharge experiments. The arrows indicate the flow of water vapor or liquid, starting with the 200 milliliters in the small, boiling flask. The large glass flask can contain any mixture of gases desired; when a voltage is applied across the electrodes in the flask, a spark jumps across the gap. The condenser consists of a jacket with cold water flowing through it.  Exercise Label the parts of the apparatus that mimic the ocean, the atmosphere, rain, and lightning.
Water droplets
Water
Trap
Heat

4. More complex organic molecules
Chemical evolution continues as HCN and H2CO react to form amino acids, sugars and nucleotides
These molecules are the building blocks or monomers needed to make the complex macromolecules found in living organisms
Experiments have shown that amino acids, sugars and purines are readily produced under early Earth conditions

5. Condensation reaction: monomer in, water out
Figure 3.8a
Condensation reaction: monomer in, water out HO
Monomer H HO H
Figure: 3.8a
Caption:
(a) In a condensation reaction, a monomer is added to a polymer to make a longer polymer. The new bond that forms results in the formation of a water molecule.  HO
Monomer H + H OH
Water

6. Polymerization of monomers into macromolecules
These condensation reactions occur readily when growing polymers stick to clay particles
Researchers have found polypeptide formation and RNA formation from the polymerization of amino acids and ribonucleic acids, respectively

7. Figure 3.6a-c Nucleotide Pyrimidines Purines NH2 O O H3C O N NH NH N5 O
Nitrogenous
base N O N O N O O– 4 1
Phosphate
group H H H 3 2
Cytosine
(C)
Uracil
(U)
Thymine
(T)
5-carbon
sugar
Purines
NH2 O
Ribose
Deoxyribose N N N NH
HO5CH2
Figure: 3.6a-c
Caption:
(a) This sketch shows the relationship between the phosphate group, the sugar, and the nitrogenous base found in a nucleotide. The numbers indicate the positions of the five carbons in the ring. Note that the nitrogenous base is bonded to carbon number 1 in the ring, while the phosphate is bonded to carbon number 5. The bond between the phosphate group and the sugar is called a 5’ linkage; the “prime” symbol indicates that the carbon being referred to is part of the sugar and not the attached nitrogenous base. Also notice that while hydrogen atoms are bonded to the carbon atoms in the ring (see part b), biologists routinely omit them to make the diagrams less cluttered. (b) Ribose and deoxyribose are similar sugars that are found in nucleotides. (c) Purines and pyrimidines are nitrogen-containing bases. A C–N bond links them to the sugar in a nucleotide. This bond forms at the nitrogen atom that is highlighted on each base. Note that purines are substantially larger molecules than pyrimidines. O OH
HO5CH2 O OH 4C H H 1C 4C H H 1C N N N N
NH2 C3 2C C3 2C H H H H H H OH OH OH H
Adenine
(A)
Guanine
(G)

8. Final step - a self-replicating molecule
A self-replicating molecule must:
Be able to catalyze polymerization reactions
Furnish a mechanism for making a copy
Most origin-of-life researchers propose the first self-replicating molecule was RNA
RNA can catalyze a variety of chemical reactions
Complementary base pairing provides a mechanism for making a copy

9. Other candidates for first self-replicating molecule
Proteins are excellent catalysts but are not capable of self- replication
DNA is an excellent template for its own replication but has no catalytic abilities

10. Figure 3.16, left RNA FORMS A TEMPLATE FOR ITS SYNYTHESIS5´ C A G U 5´ 3´
2. Copied strand polymerizes.
Template strand
Copied strand 5´ 3´
3. Copy and template separate. G C A U
Template strand
Copied strand 3´ C G A U
Template strand G C 3´ A U 5´ G C
Figure: 3.16, left
Caption:
This diagram is a hypothesis for how RNA molecules can be copied. The copying process is based on complementary base pairing between ribonucleotides. 3´ 5´
1. Complementary bases pair.

11. Figure 3.16, right Copied strand = new template New copy strand5´ 3´ 5´ 3´ C A G U
5. New copy polymerizes.
New template strand
New copy strand
6. New copy is identical to original template. 5´ 3´ C A U G
New copy strand
New template strand C G 3´ A 5´ U
Copied strand = new template G C 3´ U 5´ A G C
Figure: 3.16, right
Caption:
This diagram is a hypothesis for how RNA molecules can be copied. The copying process is based on complementary base pairing between ribonucleotides. 3´ 5´
4. Copy serves as new template.

12. What Constitutes Life?
First living organism was a cell in which controlled reactions could occur in an enclosed environment, leading to replication of the cell.
Those simple organisms would have been acted on by natural selection
Biological evolution overtakes chemical evolution

13. The earth’s environment - 4. 6 billions years ago until 2
The earth’s environment billions years ago until 2.5 billion years ago
The earth’s interior was much hotter and volcanism more frequent
Materials like iron and other unoxidized minerals were brought to the earth’s surface
These materials were were quickly oxidized
Little free oxygen remained in the environment

14. The oldest fossils Taken from rocks in Greenland 3.8 billion years old
The Greenland fossils appear to be Archaea

15. Filamentous cyanobacteria - 3.5 billion years old

16. Fossil bacteria - 3.5 billion years old

17. Stromatolites

18. Stromatolites Work of communities of photosynthetic bacteria
The bacteria secrete a sticky gel that protects them from uv radiation
Gel also causes sediment to stick
Periodically, the bacteria have to creep outward to be exposed to sufficient sunlight
The result is a cabbage-like formation

19. Stromatolites

20. The earth’s environment - beginning 2.5 billion years ago
Heat production tapered off
Crustal movements slowed and larger land masses began to form and persist
Shallow seas spread over these continental expanses, providing habitat for photosynthetic cyanobacteria
These bacteria relentlessly pumped out free oxgyen

21. The result of oxygen availability was that the earth rusted, visible in banded iron formations

22. Once the iron was all oxidized, oxygen began to accumulate
first dissolved in water
then escaping into the atmosphere
These organisms fundamentally changed the earth:
The earlier atmosphere of methane and hydrogen sulfide was replaced with an atmosphere of oxygen

23. The oxygen boom drove organisms without oxygen-handling enzymes into anaerobic habitats (stagnant waters, dead organic material, sediments)
Other bacteria evolved the ability to use oxygen to break down food into carbon dioxide and water