This video segment from Evolution: "Darwin's Dangerous Idea," together with interviews with Daniel Dennett and James Moore, depicts Darwin struggling with publicizing his revolutionary theory.

In this video segment adapted from NOVA, scientists search for carbonized remains of plants preserved in lava flows to find out how long it has taken rain forests on Hawaii to regenerate after a volcanic eruption.

This video segment, adapted from Decision in the Streets by civil rights filmmaker Harvey Richards, portrays the interracial protests that took place in San Francisco in 1963-64.

Without the work of decomposers, living organisms would eventually use up all the raw materials in the environment, and dead organisms and wastes would pile up. This video segment from Interactive NOVA: "Earth" describes the role of decomposers as the earth's great recyclers.

In this video segment adapted from ZOOM, cast members use a hair dryer to balance a ball in a stream of air, seemingly defying gravity.

In this video segment, the ZOOM cast is challenged to keep a ping pong ball in a funnel while the funnel is held upside down, seemingly defying gravity.

In this video segment adapted from Navajo Technical College, meet a dendroclimatologist who studies the relationship between precipitation and tree growth in the Navajo Nation.

In this visualization adapted from the University of Massachusetts Medical School, discover the role that dengue viral proteins play in a human cell as the virus prepares to replicate.

Why does an egg float in salt water? Learn about density and buoyancy in this video segment adapted from ZOOM.

Watch warm water float on top of cold water in this video segment adapted from ZOOM.

This video segment adapted from ZOOM offers a clever demonstration of buoyancy by showing how to pour a cup of air into a cup filled with water.

Will a grape float in oil? Will a metal nut sink in corn syrup? Watch as the ZOOM cast tests the buoyancy of a variety of liquids and objects.

This video segment from NOVA: A Desert Place describes the physical characteristics and organisms that define the desert biome.

In this video segment adapted from Design Squadí_í_íŹa PBS TV series featuring high school contestants tackling engineering challengesí_í_íŹlearn about the fundamentals of sound as student teams create percussive and stringed instruments for a local band.

In this video segment adapted from Design Squadí_í_íŹa PBS TV series featuring high school contestants tackling engineering challengesí_í_íŹstudents employ the concepts of tension and compression to build a suspension bridge without the aid of power tools.

In this video segment adapted from Design Squadí_í_íŹa PBS TV series featuring high school contestants tackling engineering challengesí_í_íŹstudents employ the concepts of tension and compression as they build a truss bridge without the aid of power tools.

In this video segment adapted from ZOOM, cast members design and build door alarms using a variety of materials, including aluminum foil, batteries, and buzzers.

In this video segment adapted from ZOOM, cast members discover that metal is a good conductor of electricity as they play the steadiness tester game.

In this video segment adapted from ZOOM, cast members make a bridge from a single piece of paper. Will it be strong enough to hold a hundred pennies?

In this video from NOVA scienceNOW, learn how scientists detect potential signs of life on distant planets.