1 .		An intriguing and controversial explanation of the evolution of Earth's atmosphere finds its roots in the hypothesis of Gaia. How does the theory of Gaia explain the evolution of Earth's atmosphere? Is it inconsistent with the explanation in Chapter 1? How does the Gaian framework explain how our planet's temperature has been relatively stable for billions of years, even though the solar energy reaching Earth has increased by 25 or 30 percent over that time?   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
2 .		One of the most exciting and controversial scientific announcements of 1996 was the discovery of chemical and morphological traces inside a meteorite that, scientists claim, indicate past life on Mars. The researchers' claim rests on the assumption that the structures and chemical traces in the meteorite were actually produced by living organisms and that the meteorite is actually from Mars. Scientists believe the meteorite is from Mars based on the similarity of gas molecules trapped within the meteorite to the composition of Mars' modern atmosphere as analyzed by the Viking lander. Based on this similarity, scientists infer that the meteorite is a piece of rock that was ejected from Mars' surface during an asteroid impact, fell to Earth, and lay frozen in Antarctica where scientists discovered it. Earth's modern atmosphere is very different from what it was years ago, so why shouldn't the same be true of Mars? Is this a reasonable consideration, and what might it imply about the claim that life once existed on Mars? Write a brief essay answering these questions. You may want to start by comparing the composition of Earth's atmosphere with that of Mars, especially with regard to oxygen and carbon dioxide. The Mars Pathfinder Lander, which arrived on Mars on July 4, 1997, sent back data on rock composition and meteorological conditions which indicate the past climate of Mars may have been different. The Life on Mars Page is also a good place to begin. [Meteorite Photo Source] [Mars Photo Source]   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
3 .		The issue of ozone depletion in the stratosphere has become a major environemental concern recently. Use web site below and section 1-2 from the textbook ("Focus on the Environment: Depletion of the Ozone Layer") to answer the following questions. Why is ozone destruction greatest above Antarctica, rather than, say, the tropics? At what time of year is the loss most severe and why? What are the four key processes by which ozone loss occurs (i.e., "The Recipe for Ozone Loss")? How long ago did ozone concentration begin to fall rapidly? Do you think that the ozone layer will recover? Why might it take some time, even if all CFC's disappeared overnight? [University of Cambridge Ozone Hole Tour]   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.
4 .		What causes the aurora borealis and aurora australis (northern and southern lights)? When are auroral events most likely to occur and where can they usually be seen? Do they occur on other planets? To help you answer these questions, visit the aurora-related sites listed at the Exploratorium and then view this aurora movie [2.7 MB] from Rice University.   To create paragraphs in your essay response, type <p> at the beginning of the paragraph, and </p> at the end.