BIOL 1202 Chapter : Chapter 25
Document Summary
Chapter 25: the history of life on earth. Earth is about 4. 6 billion years old: radiometric dating od meteorites and moon rocks. Life arose about 3. 8 billion years ago: chemical traces in rocks 3. 8 billion years, fossil bacteria 3. 5 billion years. No spontaneous generation now, but must have happened then. Atmosphere: co2, ch4, nh3, h2s, h2o, no free oxygen. Abundant energy to drive reactions: frequent storms with much lightening, frequent volcanic eruptions, frequent meteor impacts, uv light from the sun. Testable hypotheses explaining the origin of life: abiotic synthesis of small organic molecules, joining these molecules into polymers, packing these molecules into protobionts , the origin of self-replicating molecules. Alternative hypotheses: first organic compounds may have been synthesized near hydrothermal vents, extraterrestrial origin. Small organic molecules polymerize when they are concentrated on hot sand or clay. Aggregates of abiotically produces molecules surrounded by a membrane. Liposomes can form when lipids or other organic molecules are added to water: protocells.
