1. Evolution
Origin of Life on Earth

2. Dates to Know: Earth Formed- 4.6 billion years ago
Life began- approx 4.5 billion years ago

3. Geologic Time Scale

4. Conditions of Pre-Biotic Earth
Pre-biotic = Before life existed on Earth
Conditions:
High temperature
Lightning
UV light penetration
Atmosphere of methane, ammonia, hydrogen.

5. Four processes needed for the spontaneous origin of life on Earth
The non-living synthesis of simple organic molecules
The assembly of these molecules into polymers
The origin of self-replicating molecules that made inheritance possible
The packaging of these molecules into membranes with an internal chemistry different from their surroundings.

6. The experiments of Miller and Urey
Purpose- to test the hypothesis that organic molecules can form spontaneously under the right conditions.
Gases used: ammonia, methane and hydrogen, which simulated the early Earth’s environment.
Set up in a closed system conditions similar to those of pre-biotic Earth.

7. Experimental setup

8. Miller/Urey Result
It worked! Amino acids and other simple organic molecules were formed by the apparatus.
Further confirmation- in 1970 a meteorite was found to contain 7 amino acids, two of which are not found in living things on Earth.
Comets may have delivered organic compounds to Earth!

9. Where could organic compounds have been located?
Deep sea thermal vents
Volcanoes
Extraterrestrial locations

10. So…how did life actually begin?
One of the first properties of ‘life’ is the ability to replicate.
One organic molecule is naturally set up to do this…

11. RNA
Possible scenario involves randomly created monomers organizing into polymers which can then self-replicate

12. Hypothesis that the first catalysts responsible for polymerization reactions were clay minerals and RNA.
Clay contains Zinc and other substances which help it act like a template, facilitating the replication of RNA. The theory proposes that without clay, 5- chain polymer could replicate, whereas with clay, up to 20 chain polymer could replicate.

13. Clay!
1. Some clays can grow by attracting molecules to themselves-then repeat a lattice-like organization over and over again.
2. Amino Acids (AA) may have stuck to the clay lattice and been incorporated into it
Clay may have been a template for a protein
Protein= weak enzymes= speeds up protein synthesis
More and more templates to more and more proteins
Eventually RNA makes DNA
Unclear how this occurs- but it still occurs in some viruses so it is known to actually happen!!

14. RNA as the first molecule capable of replicating.
RNA is composed of a single helix, versus DNA’s double helix. The bases are exposed and ready to combine with a complement, making replication simpler that with DNA, which first requires a separation of the two strands.

15. The First Cells were Prokaryotes

16. Contribution of prokaryotes to the creation of an oxygen-rich atmosphere.
Cyanobacteria, which are photosynthetic, converted the Earth’s early atmosphere from anoxia to one which contained free oxygen. This occurred approximately 2.7 to 2.2 billion years ago.
Courtesy of Ralf Wagner

17. Origin of Eukaryotic Cells
Endosymbiotic theory- Lynn Margulis
Mitochondria were originally independent organisms, which were engulfed by another prokaryotic cell without a cell wall. Instead of being destroyed, it thrived inside and benefited the host. The relationship eventually became permanent.
Same thing for chloroplasts.

18. Other Theories- Spontaneous Generation
Spontaneous generation: the theory that living organisms could come from non-living matter ( special creation – coming from God)
Ex: flies from rotting meat, snakes and frogs in mud etc.
Existed in belief until the mid 1800’s.
Disproved by Redi and Pasteur experiments.

19. Francesco Redi- 1668 The belief was that maggots “appeared” in meat
Redi set up 2 flasks with meat, one covered and one uncovered.
The uncovered meat developed maggots after flies landed on them.
The covered meat did not develop maggots.

20. Louis Pasteur- 1859
Set up flasks with broth in a straight and curved tube.
When boiled, no bacteria grew in the curved flask. In the open flask, bacteria grew after sitting for a few days.

21. What did these prove?
These experiments proved that life could not just “appear.”
Life had to come from other life- Biogenesis.
Thus, spontaneous generation was disproved.