Introduction to “Why? The Earth” … 3 Samcheongapja Dongbangsak, 180,000 Years Old … 8 The Earth is Round … 12 How Did the Earth Come into Existence? … 19 How Did Land and Ocean Come into Existence? … 22 The Appearance of the First Organism-Precambrian Era … 26 What Kind of Organisms Lived in the Paleozoic Era? … 30 The Mesozoic Era-the Era of Dinosaurs … 32 The Cenozoic Era, When Human Ancestors First Appeared … 34 The History of the Earth in the Strata … 36 Dongbangsak’s Past … 38 Moving Continents … 42 The Earth’s Main Axis-the Mantle and the Core … 49 Volcanic Eruptions-the Earth’s Fireworks … 52 The Features of a Volcano … 58 Why Do Earthquakes Occur? … 60 What to Do in an Earthquake … 64 Mythical Continents … 68 Orogeny, the Process of Mountain Formation … 70 The Life of a Mountain … 74 The Shape of Korea … 76 What Makes Up the Crust … 78 Meandering Rivers-Erosion … 81 How Strata are Formed … 83 Fossils-Treasures Buried in the Strata … 86 Petroleum and Coal-Valuable Underground Resources … 90 Sedimentary Rocks-Layers of Rocks … 92 Igneous Rocks-Rocks Formed by Volcanoes … 94 Metamorphic Rocks-Rocks with Changed Properties … 96 Rocks That Change Due to Weathering … 100 From Rocks to Soil-The Power of Organisms … 102 Deserts-Dry Land … 106 The Circulating World of Water … 109 The Power of Water to Change Topography … 111 Subterranean Water Flows, Too … 116 Going on a Cave Exploration … 120 Hot Springs and Geysers … 123 Mountain Ranges Exist Even in the Ocean … 126 Why Does Seawater Move? … 132 What is a Trench? … 137 The Arctic and the Antarctic … 139 Our Incredible Earth … 144 The Earth is Hurting … 150 Only One Earth … 155