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Each of the 13 Unit videos introduces key scientists and their research. They provide a strong overview of the topic under discussion, and may show the actual natural systems being discussed, or illustrate the nature of a phenomenon. Through these video interviews, viewers will get a sense of how and why these scientists do their research, have a look at some of the equipment and techniques they use, and learn about recognized recent shifts in each field.

1. Many Planets, One Earth
The early Earth was a much different planet than the one we know today. Ancient rocks provide evidence to the emergence of oxygen in the atmosphere and the deep freeze of a Snowball Earth. Can these clues help explain the rise of complex animal life?

2. Atmosphere
The atmosphere makes the earth habitable. Heat trapping gases allow for ecosystems to flourish. Weather patterns, including hurricanes, help to regulate global climate. How might human emissions of greenhouse gases affect the balance of these natural systems?
3. Oceans
Ocean systems operate on a wide range of scales. Every few years, El Niño affects weather across the globe. On the small scale, tiny photosynthetic organisms near the ocean surface live and die over a 24-hour cycle. How do ocean systems regulate themselves and thus help maintain the planet's habitability?

4. Ecosystems
The abundance of diversity in tropical rainforests is astounding. How can so many species co-exist when they are competing for the same resources? And in North America, why did removing just one species change the distribution of plants and animals up and down the food web?

5. Human Population Dynamics
The human population of our planet now exceeds 6.5 billion and is rising. Much of this growth is projected for the most environmentally fragile regions of the world. Will studying the history of the world's population growth help predict the Earth's "carrying capacity" ?

6. Risk, Exposure, and Health
We require food, air, and water to survive - all of which are contaminated to some extent by man-made pollutants. We are exposed to these products all our lives, even before birth. How are these exposures impacting health, and what can be done to reduce these risks?

7. Agriculture
Will world population outrun food resources? The "Green Revolution" of the 20th century multiplied crop yields, in part, through increasing inputs of pesticides and fertilizers. How can farmers reduce their use of agricultural chemicals and still produce enough food?

8. Water Resources
While essential to the lives of humans and animals, freshwater only accounts for 6 percent of the world's water supply. Over-use and agricultural pollution threaten water resources around the globe. How can we provide the water needed for cities and crops, while ensuring the survival of the ecosystems that depend on natural water supplies?

9. Biodiversity Decline
Species are being lost at an extremely rapid rate in rainforests and coral reefs. With so many species yet to be discovered, scientists struggle to keep ahead of the bulldozers on land and the "rise of slime" in the sea. How can we protect the biodiversity of these vulnerable ecosystems?

10. Energy Challenges
Global energy use increases by the day. Polluting the atmosphere with ever more carbon dioxide is not a viable solution for our future energy needs. What new technologies will help provide the energy we need without pushing the concentrations of CO2 to dangerous levels?

11. Atmospheric Pollution
Once released, air pollution reacts chemically to become even more dangerous secondary pollutants. And these travel: nitrogen oxides from Asia affect the long-term health of Californians. How do we use what we can learn about air pollution transport to better control its impact?

12. Earth's Changing Climate
Tropical glaciers are the world's thermometers; their melting is a signal that human activities are warming the planet. Will natural ecosystems be able to absorb enough additional carbon dioxide from the atmosphere to mitigate the full impact of human-induced greenhouse gas emissions?

13. Looking Forward: Our Global Experiment
Earth's essential systems are being stressed in many ways. There are many tipping points in the environment, beyond which there could be serious consequences. Will human ingenuity, resiliency, and cooperation save us from the worst outcomes of our global experiment?

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