1. Our Earth
The universe is over 10 billion years old. Our solar system comprising the sun and nine planets including earth formed 4.6 billion years ago. The earth has a mass of 5976 million million million tonnes and an equatorial circumference of 40,075 kilometres. The earth’s crust is about 6 to 64 km thick under oceans and mountains, respectively. The crust floats on a semi molten mantle and a molten core. Oxygen is the most adundant element at 47 percent. Oceans cover 71 percent of the earth. Continental drift progresses slowly causing earthquakes, volcanoes and mountains. Rocks have mixtures of minerals. The three main rock groups are igneous, sedimentary and metamorphic. Weathering breaks rock into particles ranging in size from boulders, cobbles, gravel, sand, silt to clay. Climate significantly affects soils and vegetation.