The Earth's atmosphere is a thin layer of gases that surrounds the Earth. It composed of 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide, and trace amounts of other gases. This thin gaseous layer insulates the Earth from extreme temperatures; it keeps heat inside the atmosphere and it also blocks the Earth from much of the Sun's incoming ultraviolet radiation.

This survey of the planets includes all the basics, size, mass, atmosphere, length of day, and the like. It features interactive activities and learning exercises and compares all of the planets in colorful tables.

Even though the tundra is a frozen, windy place, animals survive there! See what animals make the tundra their home.

This comprehensive site provides a wealth of information about the seventh planet from the sun. Topics include rotational axis, size, mass and gravity, length of day, distance from the sun, and more. The information is supplemented with a number of activities that include a coloring page, quiz, and interactive puzzle.

A fantastic collection of information about the solar system. Includes information on all of the planets, the moon, the sun, asteroids, comets, meteoroids, and stars. Also find puzzles, a dictionary, quizzes, classroom activities, and crafts to do.

This study provides an orientation to the methods that are applied to control and prevent environmental pollution. The basic principles followed for eliminating negative impacts on the quality of water, air or land are discussed.

Look at the organs of the endocrine system and examine them in detail as you click on the interactive animation.

Video tutorial gives an overview of the membrane-bound structures that form the endomembrane system in eukaryotic cells. [6:19]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

On NOVA, a team of carpenters, timber framers, engineers, and historians recreate a medieval throwing machine called a trebuchet. This adapted video segment explores how understanding energy transfer informs their design. [4:17]

This interactive roller coaster ride produced for Teacher's Domain illustrates the relationship between potential and kinetic energy. As the coaster cars go up and down the hills and around the loop of the track, a pie chart shows students how energy is transformed back and forth between gravitational potential energy and kinetic energy.

This site is from the Physics Department at Georgia State University. The reliance upon the law of conservation of energy as an approach to problem-solving is presented and encouraged. It is modeled through a problem involving a free-falling object.

A laboratory experiment where students classify matter into a homogenous mixture, heterogeneous mixture, solution, or pure substance. Also students will test for physical and chemical changes.

An introduction to the Second Law of Thermodynamics focusing on terms of heat and microstates. [19:15]

Khan Academy learning modules include a Community space where users can ask questions and seek help from community members. Educators should consult with their Technology administrators to determine the use of Khan Academy learning modules in their classroom. Please review materials from external sites before sharing with students.

An extensive lesson unit on water quantity and quality and why it is important in relation to human life. Provides lessons that incorporate language, social studies, geography, and health. Tests are also provided. This is one chapter of a resource called "Let's Not Take Water for Granted" that is published by Environment Canada. It is targeted for grades 5-7 but can easily be adapted for older grades.

This site from the University of Reading provides the definition of eutrophication as well as further information about this naturally occurring phenomenon.

Grades 9-12. Learn how waterways are polluted by agricultural pesticides such as atrazine, a herbicide commonly used on corn farms, in this video segment featuring live-action animation adapted from the independent film 'Big River: A King Corn Companion.' Also, hear about health concerns related to atrazine exposure from contaminated drinking water. Includes background essay and discussion questions. [1:18]

This video segment adapted from 'Earthkeeping: Toxic Racism' looks at how pollution from an industrial hog farm impacts people who live near the farm. Learn about waste lagoons and other environmental hazards from animal feeding operations. Hear the story of how one hog farm has affected a community in North Carolina and how residents sued the farm for violations of the Clean Water Act. In addition, learn about how minority communities are unfairly affected by environmental issues. Includes background essay and discussion questions. [3:16]

Follow a Dallas community's fight to receive federal Superfund status to clean up the damage from a high-polluting lead smelter in this video segment adapted from Earthkeeping: "Toxic Racism." Hear from a reporter from the National Law Journal who explains some of the health effects of lead exposure and how after a cursory cleanup of a lead smelter site in West Dallas, the community was ignored, despite warnings from the Centers for Disease Control about elevated blood lead levels. Meet Luis Sepulveda, a community member who organized the West Dallas Coalition for Environmental Justice, which eventually succeeded in having the site win Superfund status. Includes background essay and discussion questions. [3:48]

Modern farming has helped feed the world, but along the way, the land has suffered, according to this video adapted from the series 'Race to Save the Planet.' When farmers grow too much too fast, topsoil is depleted. Farmers can work around this problem with fertilizers, irrigation, and pesticides, but these create new problems. Pesticides can harm wildlife, linger on fruits and vegetables, or wash into water supplies. Farmers are now finding new approaches to raising food, like diversifying crops, applying organic fertilizers, and finding alternatives to pesticides. Includes background essay and discussion questions. [1:23]

Learn how farm runoff impacts water quality and human health. Tour the water treatment plant in Des Moines, Iowa, and learn how the water is filtered, in this video excerpted from the independent film 'Big River: A King Corn Companion.' Hear how high nitrate content in water can affect human health, causing such problems as blue baby syndrome, and understand why water treatment plants in agricultural regions need nitrate removal facilities because of the pollution from fertilizer runoff. Includes background essay and discussion questions. [2:03]