To The heartbeat of earth
Here, powered by the Sun, is the biosphere of Earth. Here are all of the microbes and all of the plants, humans, and other animals that arose much later under a protective ozone layer produced by microbes. Here, where this story began in Yellowstone National Park, is a pack of gray wolves running in the mountains above Lamar Valley at sunset. As darkness falls, the wolves begin to stalk a group of American bison. The bison stand at the top of a ridge, halfasleep and completely unaware of the wolves, who have encircled a newborn calf. With a signal from the alpha male, the wolf pack bursts into action. Racing up the hill, the wolves’ muscle cells are powered by mitochondria—by a bacterial endosymbiont that joined with another microbe long ago to form the eukaryotic cell. The wolves tear the calf from the herd, but the calf fights back. With every breath FIG 2.17f (opposite) The Great Salt Lake mud biofilm as seen with electron microscopy. The large, glass-shelled cells are diatoms. Many smaller species of bacteria and archaea live within the surrounding biofilm.