2Key ConceptsEnergy and matter flow through Earth’s four spheres: the geosphere, atmosphere, hydrosphere, and biosphere.Energy flows through the atmosphere and hydrosphere mostly by convection.
3Earth: An OverviewEarth is the only planet known to have abundant liquid water on its surface.Water covers about 71% of Earth’s surface.The water is called the global ocean.The global ocean is part of Earth’s hydrosphere.The hydrosphere is the portion of Earth that is water.
4The biosphere is the portion of Earth where life exists. The atmosphere is a mixture of gases that surround Earth.The geosphere is the mostly solid, rocky part ofEarth.All of Earth’s water is part of the hydrosphere.Energy and matter are cycled between these four spheres.
5The Geosphere The geosphere is divided into layers. Compositional layers are based on chemical composition.Physical layers are based on physical properties.
7The AtmosphereThe atmosphere is a mixture of invisible gases that surround Earth.The atmosphere extends outward to about 500 km from the surface of Earth.Most of the atmospheric gases lie within 8 to 12 km of Earth’s surface.
8Atmosphere The troposphere is the atmospheric layer in which we live. It extends outward to about 12 km from Earth’s surface.Weather usually occurs in the troposphere.
9The stratosphere is the layer directly above the troposphere. Temperatures in the stratosphere increase with altitude.The mesosphere is above the stratosphere.
10The mesosphere is the coldest layer of the atmosphere. The thermosphere is the uppermost layer of the atmosphere.Temperatures in the thermosphere increase with altitude.
11Energy Flow in the Atmosphere Solar radiation heats Earth’s surface unevenly.Uneven heating causes air in the atmosphere to move.As cold air sinks, it forces warm, less-dense air upwards.
12This movement of air distributes energy throughout the atmosphere. The transfer of energy, especially heat, due to the movement of matter, such as air, is called convection.
13The Hydrosphere All of Earth’s water is part of the hydrosphere. More than 97% of the water on Earth is in the global ocean.The global ocean covers a surface area of about 335 million square kilometers.
14Energy Flow in the Hydrosphere Solar radiation heats ocean water unevenly.The temperature of ocean water varies from warm at the equator to near freezing at the poles.The temperature of ocean water also decreases with depth.
15Differences in density and the concentration of salts in the ocean affect the density of ocean water.Differences in the density of ocean water causes movement called convection currents.Convection currents distribute energy in the ocean.
16The Biosphere The biosphere contains all life on Earth. The biosphere includes Earth’s surface, the lower part of the atmosphere, and most of the hydrosphere.The biosphere has certain factors that organisms need in order to live.
17Liquid water, suitable habitat, and moderate temperatures are important to most organisms. A stable source of energy is also important.Plants and algae obtain energy from sunlight, other organisms obtain energy by eating other organisms.
18Energy enters the biosphere as sunlight. Plants and algae change this energy into chemical energy through the process of photosynthesis.Then, the energy is passed to organisms that eat plants and algae.
19Energy and matter is also passed to other organisms when they eat each other. Dead organisms are consumed by decomposers, such as bacteria and fungi.Materials broken down by decomposers, such as carbon dioxide, are used by plants to make food during photosynthesis.