Earth Sciences 1022a - Lecture Brief - 15 Sep 09 INTRODUCTION TO PHYSICAL GEOLOGY AND PLATE TECTONICS Why? Geology (study of Earth) is important for energy and natural resources, solving environmental problems, building cities and highways, predicting and protecting against natural disasters like earthquakes, volcanic eruptions, landslides, floods Uniformitarianism: fundamental principle “the present is the key to the past” How long? geologic time is measured in billions of years Where and How? After the Big Bang (15-20 billion years ago) Earth may have formed by the nebular hypothesis: ~5 billion years ago a solar nebula of hydrogen and helium gravitationally contracted into a rotating disc with our Sun at the centre, and the planets and moons revolving around it • within the disc, Earth evolved through many collisions of rocky and metallic fragments into a rocky sphere divided into a dense core , large mantle , and lighter crust Plate Tectonics: the crust and uppermost mantle eventually split into rigid plates of
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