1900 Air Pollution

Examine this graph from FRONTLINE/NOVA: "What's Up with the Weather?" Web site to see dramatic increases in three greenhouse gases over the last two hundred years.

The Advantage of Sex

Why did sex evolve? The likely answers, in this essay for the Evolution Web site by science journalist Matt Ridley, may surprise you.

Amazing Heart Facts

This feature from the NOVA "Cut to the Heart" Web site highlights facts about the heart -- including its size and placement -- and will help you to understand the importance of this wondrous organ in our bodies.

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Animal Body Plans: Homeobox Genes

The homeobox genes that define the basic body plan of mice and fruit flies are illustrated in this graphic from The Human Evolution Coloring Book by Adrienne Zihlman. The accompanying article describes how these genes act as "molecular architects" in all animal species.

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Astronauts in Hard Hats

This media-rich series of interviews from the NOVA Web site explores the unique challenges faced by astronauts doing construction work in outer space.

Atmospheric Carbon Dioxide Levels

Earth is warming because of an increase in greenhouse gases, including carbon dioxide (CO₂). Explore what can be done to slow or stop continued climate change.

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Atmospheric Pressure

Did you know that air has weight? This illustrated essay from the NOVA Web site explores conditions that affect air density and atmospheric pressure.

The Beginnings of the Telescope

This animated essay from the NOVA Web site examines the design of Galileo's refracting telescope and Sir Isaac Newton's reflecting telescope.

Buoyancy Basics

This illustrated demonstration from the NOVA Web site explains the concepts of buoyancy and density by showing what happens when different kinds of wood blocks are dropped in water.

Chernobyl: What Really Happened?

This text excerpted from Richard Rhodes' book, Nuclear Renewal and reprinted on the FRONTLINE Web site examines the causes of the Chernobyl accident.

Chris Schneider: Rethinking Conservation

In this interview filmed for Evolution: "Darwin's Dangerous Idea," biologist Chris Schneider discusses the relationship between conservation and speciation.

CO₂ Concentrations at Mauna Loa Observatory, Hawaiʻi

This resource, adapted from the Carbon Dioxide Information Analysis Center, provides a graph of monthly average carbon dioxide (CO₂) concentration from 1958 to 2000 at the Mauna Loa Observatory in Hawaiʻi.

Complex Relations

In this text excerpted from chapter 3, "Struggle for Existence," of Charles Darwin's On the Origin of Species, Darwin draws on firsthand and historical information for his observations about evolution.

Convergence: Marsupials and Placentals

This graphic illustrates some of the marsupial mammals in Australia and placental mammals in North America. Even though they are not closely related, these mammals look alike because they have adapted to similar ecological roles. From The Human Evolution Coloring Book by by Adrienne Zihlman.

Dab of DNA Helps Keep Counterfeiters at Bay

Find out in this USA Today article how DNA sequences can vouch for a souvenir's authenticity.

Darwin's Letters: Collecting Evidence

This group of letters is a sample of the extensive correspondence Darwin carried on with a wide group of friends and colleagues as he collected evidence to support his theory of evolution by natural selection. From Charles Darwin's Letters: A Selection 1825-1859.

Darwin's Letters to Lyell

In this letter written to his friend and mentor Charles Lyell less than three weeks after the publication of On the Origin of Species, Darwin describes the reaction of the great anatomist Richard Owen to his theory. From Charles Darwin's Letters: A Selection 1825-1859.

The Dating Game: Radioactive Carbon

In this media-rich essay from the NOVA Web site, learn about the atomic structure of radioactive carbon and how it can be used to determine the age of organic remains, such as bones and teeth.

Decreasing California Snowpack

Approximately 40 percent of California's surface water supply originates from the snowpack in the Sierra Nevada Mountains. However, climate change is significantly altering this precious water source.

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Demolition Woman

Find out how controlled explosions are used to demolish multi-story buildings in this interview from the NOVA Web site.