Carbon Cycle Diagram

This diagram from NASA Earth Science Enterprise illustrates Earth's carbon cycle.

Cave Formation: Biogeochemical Cycles

This video segment adapted from NOVA chronicles the discoveries that led to a radical new theory in which living organisms, not just geological processes, play an active role in cave formation.

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Cave Formation: Kane Cave

This video segment adapted from NOVA describes a simple experiment that confirmed the idea that microbes can accelerate the biogeochemical process of cave formation.

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Caves: Extreme Conditions for Life

This video segment adapted from NOVA raises the provocative idea that if life can exist in the most extreme environments on Earth — such as in dark, toxic caves — then perhaps living things can also survive in harsh environments on other planets.

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Deep-Sea Vents and Life's Origins

Deep-sea vents are home to life forms that do not rely on the Sun's energy. They depend instead on energy from volcanoes on the ocean floor. This video segment adapted from NOVA hypothesizes that life on Earth may have begun in this extreme environment.

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Earth as a System

This visualization adapted from NASA maps progressive global changes onto a rotating globe. Earth's atmosphere, hydrosphere, geosphere, and biosphere are shown to be dynamic and interconnected.

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Global Trends Quiz

In this interactive quiz from NOVA, take the Environmental Challenge and test your knowledge of human impact on the world's natural resources and climate.

Global View of the Seasons

This interactive activity produced for Teachers' Domain features satellite data of Earth's seasonal cycles. Visualizations and comparative still images reveal how successfully plants are photosynthesizing at different times of the year.

Health Risks of BP Oil Spill

In this video segment adapted from Need to Know, learn about the possible short- and long-term health risks for workers involved in cleaning up the BP oil spill in the Gulf of Mexico.

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Life Before Oxygen

This video segment adapted from Interactive NOVA features evidence of life on Earth before the atmosphere contained a rich supply of oxygen.

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Life's Little Essential: Liquid Water

Why is water necessary for life? Why is it the best and possibly only liquid to do the job? This illustrated essay from NOVA Online answers these questions, explaining why planetary scientists are on the lookout for water elsewhere in the solar system.

Mass Extinction

In this video segment adapted from NOVA scienceNOW, learn about a chain of events, including ancient volcanoes, global warming, and deadly gases, which may have caused Earth's greatest mass extinction 250 million years ago.

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The Mississippi River Delta

These images from NASA, the Lunar and Planetary Institute, and U.S. Geological Survey illustrate the effects of severe storms and decades of river management on the size and shape of the Louisiana coastline and the Mississippi River Delta.

Nature's Kidneys

This video shows how wetlands cleanse the ecosystem in ways similar to how kidneys cleanse the human body.

Nature's Supermarket

This video shows a sample of the large varieties of plants, animals, birds and fish that abound in wetlands and looks at the processes that sustain them.

The Nitrogen Cycle

Nitrogen, one of the most abundant elements in the universe, is essential to life. This interactive activity adapted from the University of Alberta provides an overview of the nitrogen cycle.

Snapshot of U.S. Energy Use

This video segment adapted from NOVA/FRONTLINE looks at American energy consumption and the resulting production of greenhouse gases.

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Soil Microbes and Global Warming

In this video adapted from KUAC-TV and the Geophysical Institute at the University of Alaska, Fairbanks, discover how warmer winters in Alaska may cause soil microbes to release more carbon dioxide into the atmosphere, contributing to global warming.

Soils Around the World

Not all soils are the same. This interactive activity produced for Teachers' Domain features photographs of the 12 major soil types and maps that highlight their distribution around the world.

The Wall of Time

This illustrated timeline from the Lunar and Planetary Institute provides a journey through four-and-a-half billion years of time from the birth of our solar system to its current existence today.