Chapter One

TO THE ENDS OF EARTH

The totality of life, known as the biosphere to scientists and creation to theologians, is a membrane of organisms wrapped around Earth so thin it cannot be seen edgewise from a space shuttle, yet so internally complex that most species composing it remain undiscovered. The membrane is seamless. From Everest's peak to the floor of the Mariana Trench, creatures of one kind or another inhabit virtually every square inch of the planetary surface. They obey the fundamental principle of biological geography, that wherever there is liquid water, organic molecules, and an energy source, there is life. Given the near-universality of organic materials and energy of some kind or other, water is the deciding element on planet Earth. It may be no more than a transient film on grains of sand, it may never see sunlight, it may be boiling hot or supercooled, but there will be some kind of organism living in or upon it. Even if nothing alive is visible to the naked eye, single cells of microorganisms will be growing and reproducing there, or at least dormant and awaiting the arrival of liquid water to kick them back into activity.

An extreme example is the McMurdo Dry Valleys of Antarctica, whose soils are the coldest, driest, and most nutritionally deficient in the world. On first inspection the habitat seems as sterile as a cabinet of autoclaved glassware. In 1903, Robert F. Scott, the first to explore the region, wrote, "We have seen no living thing, not even a moss or lichen; all that we did find, far inland among the moraine heaps, was the skeleton of a Weddell seal, and how that came there is beyond guessing." On all of Ea