Our Rare Earth
In the beginning, namely the Big Bang, conditions were so violent that only simple atoms like hydrogen and later helium survived. So where did all the other elements come from?
The simple answer is that they were "cooked up" by stars much larger than ours, stars that then exploded and spread their products into the cosmos. These exploding stars are called supernovas.
http://en.wikipedia.org/wiki/Supernova
Our own star, the Sun, and its planets happily were formed from supernova dust that was rich in heavy elements. Some star and planet systems, especially in earlier universe times, were not so fortunate, and their Periodic Tables had many gaps.
Additionally, had we come along sooner in the universe, both quasars and supernova explosions would have been hazardous and sterilized our Earth. Had we come later, the probability of having plate tectonics would have decreased dramatically. As we shall discuss later, plate tectonics have been vital to the sustained temperatures on Earth over billions of years.
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