of years ago the earth's atmosphere had no oxygen. Bacteria like
the purple and red species seen in one section of the exhibit inhabited
the worlds surface. They extracted energy from sulfur compounds.
Over time, green bacteria, like those that are observed in another
section of the exhibit, began to extract energy from water and produce
oxygen as waste. By introducing oxygen into the atmosphere, the
green bacteria poisoned large numbers of the other bacteria. But
they also paved the way for oxygen breathing organismslike