The Structure of Earth • When Earth formed about4.6billion years ago, gravity caused the compression of dust and gases and created very high temperatures. • Heavier elements were pulled into the center, and lighter elements collected near the surface. • The lightest elements, gases, formed the outermost layer of the planet. • With time, the outer layer of gases formed the atmosphere, and Earth’s molten surface cooled and hardened. • The interior of the Earth remains extremely hot.
The Earth’s Layers • Crust: the outer rocky surface, ranges from about 6km (4 mi) under oceans, up to 90 km (56 mi) thick under mountain ranges. The rocks of the crust-primarily granite-are relatively low in density. • Mantle: beneath the crust, a layer of more dense rock about 2,900 km (1,800 mi) thick. The mantle is solid but parts are somewhat molten and flow in slow-moving currents.
The Earth’s Layers • Outer Core: found under the mantle, is about 2,240 km (about 1, 400 mi) thick and is composed of dense, molten rock-mostly iron, nickel, and silicon. • Inner Core: the innermost layer of Earth, is about 2,440 km (about 1,540 mi) in diameter. This part of the Earth is solid due to the intense pressure there, which is about 4 million times greater than at Earth’s surface.
Earth’s Weathered Crust • Weathering: a process in which the rock that makes up Earth’s crust is exposed to the elements and gradually breaks down. • Mechanical Weathering: the physical breakdown of rocks into smaller pieces, gradually reducing them to the tiny particles that make up soil. The rocks still have the same chemical composition as the original rock. Wind, water, plants, and temperature and pressure changes all cause mechanical weathering.
Earth’s Weathered Crust • Chemical Weathering: the breakdown of rocks caused by chemical reactions with other substances. It results in a change in the chemical composition of rocks. Rainwater, oxygen, and acid rain all cause chemical weathering.