Planet Earth Getting to Know Earth The atmosphere, hydrosphere, and lithosphere form the biosphere, the part of Earth that supports life for all people, animals, and plants. Atmosphere is a thin layer of gases that surround Earth and contains the air we breathe. Hydrosphere includes the liquid and frozen surface water, groundwater, and water vapor in and around oceans, lakes, and rivers on Earth. Lithosphere is the land or surface areas on Earth, including the continents, islands, and ocean basins.

Planet Earth Getting to Know Earth The atmosphere, hydrosphere, and lithosphere form the biosphere, the part of Earth that supports life for all people, animals, and plants. Atmosphere is a thin layer of gases that surround Earth and contains the air we breathe. Hydrosphere includes the liquid and frozen surface water, groundwater, and water vapor in and around oceans, lakes, and rivers on Earth. Lithosphere is the land or surface areas on Earth, including the continents, islands, and ocean basins.

Forces of Change Earth’s Structure For millions of years, the surface of the Earth has been moving. The Earth is composed of three layers—the core at Earth’s center, the mantle layer of dense rock on the outer core, and the crust forming Earth’s surface. Many scientists believe Earth was once a single land mass called Pangaea, but then continental drift slowly spread the continents apart. Plate tectonics describes the activities of continental drift and magma flow; referring to the physical processes that create and shape continents, islands, oceans, and mountain ranges.

Internal Forces of Change Mountains are formed when Earth’s giant continental and oceanic plates collide. Moving plates sometimes cause Earth’s surface to buckle forming folds; in other cases the moving plates form cracks called faults. Violent movements of Earth’s crust along fault lines are called earthquakes, which dramatically change the surface of the land and the floor of the ocean. Volcanoes are mountains formed by lava or magma that breaks Earth’s surface. Forces of Change

External Forces of Change Wind and water break down the Earth’s surface through weathering and erosion. Physical weathering happens when large masses of rock are broken down into smaller pieces. Glaciers are large bodies of ice that move across the Earth’s surface, changing the landscape as they flow. Soil building takes thousands of years of weathering, erosion, and biological activity and is influenced by five factors; climate, topography, geology, biology, and time. Forces of Change

Earth-Sun Relationships Climate and Weather Weather is the condition of the atmosphere at a specific time. Climate refers to the average weather conditions over many years. Earth’s tilt on its axis in relation to the sun affects temperatures from day to night. The rotation of Earth around the sun takes one year; this revolution affects temperatures from season to season.

The Greenhouse Effect The greenhouse effect allows trapped atmospheric gases to radiate heat that warms the Earth. Under normal conditions, the atmosphere naturally provides enough insulation to promote life on Earth. The radiation the Earth receives from the sun must equally balance with the heat radiated back into space to avoid temperature extremes in order to support life. Earth-Sun Relationships