Three billion years ago single-celled underwater bacteria used sunlight to convert carbon dioxide and water into tiny oxygen bubbles. Soon plants were turning an atmosphere full of volcanic carbon dioxide into oxygen. As we learn in this video segment from Interactive NOVA: "Earth," photosynthesis created a good home for animals and humans, though not for some primitive organisms. They had to retreat to where oxygen couldn't reach them. Join researchers as they search for these organisms, now considered tiny time capsules from a time before there was oxygen on Earth.

In this video segment adapted from NOVA, scientists are startled to discover evidence for the three key ingredients for life on Saturn's moon Enceladus.

How can you lift a heavy metal table using air? In this video segment adapted from ZOOM, cast members succeed in lifting a table using their own breath and a few plastic bags.

This video segment adapted from Shedding Light on Science describes how astronomical distances can be measured in units of light-years, and how the finite speed of light allows astronomers to study how the universe looked long ago.

This video segment adapted from Shedding Light on Science demonstrates the law of reflection by showing how light energy is reflected off both smooth and rough surfaces at predictable angles.

What is it that distinguishes a living organism from a nonliving object? This collection of images presents examples that aren't as clear-cut as one might think, enticing students to question the meaning of life.

In this video segment adapted from the Alaska Native Heritage Center, discover the connections between Alaska Native subsistence culture and the natural cycle of the seasons.

This video, adapted from material provided by the ECHO partners, illuminates how living on the coast affects individuals and communities, particularly humans' interrelationships with natural resources.

In this interactive activity adapted from Annenberg Learner’s Teaching Math Grades 6–8, students interpret two line graphs to identify possible locations where the data might have been gathered.

In this adapted ZOOM video segment, cast members get hands-on in the recycling process by using old newspapers to make new paper.

In this video segment adapted from ZOOM, cast members make a seismometer and experiment with different ways to make it register movement.

This video adapted from NASA explains how a magnetometer determines magnetic fields around planets.

This video segment from NOVA: "The Mystery of Animal Pathfinders" explores how the migratory patterns of shorebirds have evolved to coincide with the spawning of horseshoe crabs.

Two astronauts aboard the International Space Station (ISS) describe mass and weight and the differences between the two in this video from NASA’s Teaching From Space initiative.

This video segment adapted from Discovering Women profiles Fermilab physicist and Harvard professor Melissa Franklin.

All animals develop and grow over time. The animals in this video segment, however, undergo very dramatic changes on their way to adulthood -- a developmental process known as metamorphosis.

Learn about an important physics experiment that uses an invention that manipulates light in this interactive activity adapted from NASA.

In this video from DragonflyTV, Tiana and Sammy measure, record, and analyze the results of a drop box test to find out how everyday items behave in microgravity.

This video segment from NOVA: "The Mystery of Animal Pathfinders" explores the migratorial exploits of monarch butterflies.

This video segment, adapted from NOVA scienceNOW, introduces the latest research on a system of neurons that plays a part in how people relate to each other.