1. Chapter 26. The Origin of Life
AP BIOLOGY 11
Chapter 26. The Origin of Life

2. CHEMISTRY TO BIOLOGY
Video

3. Origin of the Earth
The Earth formed about 4.7 billion years age by accretion of debris left over from the formation of the sun

4. Origin of the Earth
Gravity collapsed earth’s mass producing tremendous heat which liquefied all the matter.

5. The Earth Cools
Hundreds of millions of years of torrential rains finally cooled the Earth to the point where a solid crust could form.
The Earth is still cooling with our crust only km thick
The Earth Structure Today

6. The Primordial Earth
The newly formed crust was thin and cracked resulting in tremendous volcanic activity.
The atmosphere contained CO2, NH3, CH4 and superheated steam - storms raged.

7. Chemical Evolution The Primordial “Soup”
Gasses in the primordial atmosphere reacted to produced a variety of organic compounds including: amino acids, monosaccharides, lipids, and nucleotides.
Supporting evidence: Miller’s expts.

8. Chemical Evolution
Organic monomers accumulated in the hot early oceans, chemical reactions created polymers from monomers.
Polysaccharides, lipids, proteins, and nucleic acids as well as many others formed.
Macromolecules arose

9. Chemical Evolution
Liposomes - spheres made from phospholipids mixed with water (bilayers like cell membranes)

10. Chemical Evolution
Coacervates - colloidal drops of polypeptides, nucleic acids and polysaccharides
These had most of the characteristics of life

11. Protocells With protocells, we could say life existed.
All protocells at this point were heterotrophs and lived in the warm oceans

12. Protocells
The first genetic material was likely RNA, but it is small and can’t code a lot of info.
DNA arose as a mutation and would be strongly selected for as it can code for such masses of information.

13. Photosynthesis Arises
Life would have stopped as the heterotrophic cells consumed all available organic matter.
A new energy source was needed.
Utilize of light energy was needed, an advantage that would be selected for.
Soon two basic life pathways: heterotrophic and autotrophic
cynobacteria

14. The Oxygen Revolution
As photosynthesis gathered steam, O2 began to accumulate in the atmosphere.
This resulted in two major changes critical for life to evolve beyond the most simple levels.

15. The Oxygen Revolution 1. Development of the Ozone Layer
O2 reacts with UV in upper atmosphere to form ozone, O3.
3 O UV---> 2 O3
This results in the accumulation of ozone above the stratosphere

16. The Oxygen Revolution
The ozone absorbs UV and protects life on the surface from the harmful effects of such intense UV
The result is “Genetic Stability” for life

17. The Oxygen Revolution 2. Aerobic Respiration
Switching from a reduced O2 atmosphere to a rich O2, allowed life to use O2 more efficiently in producing energy .
Glucose ---- no O2--> CO2 + H2O + 2 ATP
Glucose ----O2----> CO2 + H ATP
This provided the energy necessary for the evolution of complex life on Earth

18. Conclusion
There were now two basic life strategies on Earth: heterotrophic and autotrophic.
With the oxygen revolution, all was in place for the explosive evolution of the pre Cambrian and Cambrian.

19. Conclusion
One of the places that this explosion is best preserved is in the Burgess Shale here in BC (Glacier Nat. Park)