1. HISTORY of LIFE

2. Before Life… Land Environments
Earth was molten when it formed about 4.6 billion years ago
After 500 million years, a solid crust formed
Too much heat for life to exist

3. Before Life… Atmosphere Gasses in atmosphere came from volcanoes
Water vapor, carbon dioxide, methane, ammonia gas, nitrogen, hydrogen, etc.
The early atmosphere was anaerobic (it had little or no free oxygen)

4. Origins of life: Early Ideas
Where did the first living things come from?

5. Aristotle (384 –322 BC) Proposed the theory of spontaneous generation
Also called abiogenesis
Idea that living things can arise from nonliving matter
Idea lasted almost 2000 years

6. Disproving Spontaneous Generation

7. 1668: Francisco Redi filled six jars with decaying meat.
Conditions:
Results:
3 jars covered with a lid
No maggots
3 open jars
Maggots appeared
In a jar without a lid, maggots appeared in the meat because adult flies had laid eggs and more adult flies soon appeared

8. Franciso Redi

9. 1765: Lazzaro Spallanzani boiled nutrient solutions in flasks.
Conditions:
Results:
Nutrient broth placed in flask, heated, then sealed
No microbial growth
Later, he broke the seals & the
soups became cloudy with microbes.
Critics said sealed vials did not allow enough air for organisms to survive and that prolonged heating destroyed “life force”

10. Lazzaro Spallanzani

11. 1861: Louis Pasteur demonstrated that microorganisms are present in the air.
Conditions:
Results:
Nutrient broth placed in s-shaped flask and heated
No Microbial growth
Nutrient broth placed in s-shaped flask, heated, flask opened
Microbial growth
S-shaped flask kept microbes out but let air in. Proved microbes only come from other microbes (life from life) - biogenesis

12. Louis Pasteur

13. Origins of life: Modern Ideas
If life can arise only from pre-existing life, then how did the first life form appear?

14. Life originated through a series of early chemical events
Simple organic molecules simple metabolic pathways emergence of life

15. Stanley Miller & Harold Urey (1953)
First scientists to show that simple organic compounds (macromolecules) could be made from inorganic compounds

16. Miller & Urey (cont’d)
Filled apparatus with water and gases from early atmosphere
Electric discharges simulate lightning for energy
Resulting mixture contained organic compounds including amino acids.

17. The First Cells The first cells were anaerobic prokaryotes ( bacteria)
Eukaryotic cells first appeared about 1.8 billion years ago when oxygen became a part of Earth’s atmosphere

18. The Endosymbiont Theory
Proposed in 1966 by Lynn Margulis
States that a long time ago prokaryotic cells engulfed (took in) other prokaryotic cells.
Once inside, the two cells formed a permanent relationship that formed eukaryotic cells

19. Evidence for the Endosymbiont Theory
Mitochondria & Chloroplast
Contain their own circular DNA (similar to bacteria)
Have their own ribosomes
Can reproduce independently of the cell by binary fission
(The same way
bacteria reproduce!)

20. HOMEWORK
History of Life Notes - Notes Assignment # 1