The Evolutionist Theory of the Origin of Life Packet #31

Geologists & The Early Earth Biologists generally agree that life originated from non-living matter. Chemical Evolution Is very difficult to test experimentally Four Requirements Little or no free oxygen A source of energy The availability of chemical building blocks Water Minerals Gases present in the atmosphere (All necessary to form organic molecules) Time Necessary for molecules to accumulate and react.

Chemical Evolution During chemical evolution, small organic molecules formed spontaneously and accumulated There are two hypotheses proposed Prebiotic Soup Hypothesis Organic molecules formed near Earth’s surface in a “sea of organic soup” or on rock or clay surfaces. Iron-sulfur World Hypothesis Suggests that organic molecules were produced at hydrothermal vents Cracks in the deep ocean floor

Major Steps in the Origin of Cells After small organic molecules were formed Macromolecules were assembled from the small organic molecules. Protobionts were formed from the macromolecules Macromolecular assemblages Cells then arose from the macromolecular assemblages RNA World Model RNA was the first informational molecule to evolve in the progression towards a self-sustaining and self-supporting cell Natural selection at the molecular level resulted in the information sequence DNA-->RNA-->protein

How the Evolution of Photosynthetic Autotrophs affected Both the Atmosphere and Other Organisms The first cells, prokaryotic heterotrophs, obtained organic molecules from the environment. Anaerobes Later, autotrophs arose Organisms that produce their own organic molecules by photosynthesis. The evolution of photosynthesis ultimately changed early life because it generated oxygen This oxygen produced accumulated in the atmosphere Allowed the evolution of aerobes Organisms that use oxygen for a more efficient cellular respiration.

Endosymbiont Theory Eukaryotic cells arose from prokaryotic cells. Certain organelles found within eukaryotic cells evolved from prokaryotic endosymbionts with larger prokaryotic hosts.

The Geologic Record Know Table 26.1 on page 519 Chapter 26