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Overall Context
In order to understand how the Universe has changed from its initial simple state following the Big Bang into the magnificent Universe we see as we look at the night sky, we must understand how stars, galaxies, and planets are formed over time. The Universe is comprised of mostly hydrogen and helium. In fact, these two elements make up 98% of the visible matter in the Universe. Nevertheless, our world and everything it contains—even life itself—is possible only because of the existence of heavier elements such as carbon, nitrogen, oxygen, silicon, iron, and many, many others. How long did it take the first generations of stars to seed our Universe with the heavy elements we see on Earth today? When in the history of the Universe was there a sufficient supply of heavy elements to allow the formation of prebiotic molecules and terrestrial-like planets upon which those molecules might combine to form life?
Our big question: "How did the universe originate and evolve to produce the galaxies, stars, and planets we see today?"