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Age of Earth: BIO chapter 12 Earth’s Age: • 4.6 Billion years • Measured age of rocks • Radiometric dating-using isotopes and half-life that produce radiation and energy Chemicals: • Basic building blocks of life-CHO • Is thought by some that organic molecules have formed from non-living molecules Three Life beginning models: 1. Primordial soup model-organic molecules formed spontaneously with added energy- water and sunlight **scientists today still disagree on origin of life Life beginning models: 2. Miller-Urey model-atmospheric material could make organic compounds-no ozone problem-water and electricity Life beginning models: 3. Bubble model-cycle of gases forming in ocean water releasing chemicals into the atmosphere- water and volcanoes Microspheres: • A. A. formed in tiny droplets • 1st step toward cellular organization • Thought that RNA formed from DNA First Life froms • Thought to appear 2.5 billion years ago Sequence of formation: • anthropods-vertebrates-fish-amphibians-reptiles-birds-mammals Extinction: • 5 periods of extinction on Earth so far • Extinction-one species dies out • Mass extinction-many species die