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

CHEMISTRY TO BIOLOGY Video

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

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

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 5 - 64 km thick The Earth Structure Today

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.

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.

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

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

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

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

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.

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

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.

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

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

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 + H20 + 36 ATP This provided the energy necessary for the evolution of complex life on Earth

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.

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