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plants. As for the cycling of carbon, the planet’s basic machinery keeps these other elements cycling and provides civilization with these critical ingredients for life. Here again, our dynamic planet stands alone. As far as we know, ours is the only planet with the machinery for recycling nutrients from plants to animals and to soil, rocks, and the air and back again to plants.
    Both nitrogen and phosphorus have their own distinct life-enabling recycling machinery. But the two cycles are alike in one key respect: the pace at which they operate has constrained humanity’s ability to feed itself for nearly all of human history. The incredible lengths that people have gone in the effort to manipulate the machinery—among them hauling buckets of human waste from Chinese towns back to farms, scavenging bison skulls across the North American prairie, and bribing German factory-workers to reveal industrial secrets—have resulted in some of the most profound of humanity’s achievements and changed civilization’s course. We’ll return to these achievements in later chapters.
    Time to Fill the Pantry
    A stable climate over geologic time and the recycling apparatus for life’s essential nutrients are two of the fundamental foundations for ourplanet’s success, and therefore for our success. But there is a third requirement for the success of a species like Homo sapiens : an abundance of plants and animals that can be manipulated for the benefit of our species.
    Think of the fruits, vegetables, grains, dairy products, and meat in grocery store aisles. You’ll be able to count the number of species on a few hands: mostly corn, wheat, rice, cows, pigs, chickens, and a few others. Even considering fruit and vegetable species, the total is only a tiny percentage of all the species on the planet. These are the species that grow fast enough and are easy enough to collect to make them possible to cultivate on a large scale. But the small number that we eat belies the importance of the diversity of life.
    Other, less edible species carry out essential functionsthat we cannot live without. Imagine a world without the fungi to decompose dead leaves and branches. We would be buried in debris. Without the species that prey on the pests that eat crops, like the ladybugs that eat aphids and mites, we would have to share more with those nuisances. Bees, beetles, and butterflies fly from flower to flower carrying pollen grains that enable almonds, apples, squash, and many other crops to reproduce. The diversity—even redundancy—of life, with multiple species performing the same function, provides humanity with insurance that if climate change or some other catastrophe wipes out some, there will still be others to do the job. And we need not just a few specimens of each species—we need many. Diversity of genes across individuals ensures that when diseases or other problems arise, some members of a species will withstand the onslaught and survive. These supporting roles are just a few of those performed by species that are not found on the grocer’s shelf. Without these supporting species, humanity would not be able to feed itself. And the functions of the millions of known species, and the millions yet to be discovered, remain largely unknown. Little noticed, these worker species make the difference between a fulland an empty plate.
    Today’s Earth teems with life. Life is found in places as varied as the deep sea and glacial ice. No one knows how many species exist on Earth, probably somewhere between 5 and 30 million. The overwhelmingly vast majority of species are the creepy, crawly variety. Species of beetles alone may number half a million. Then there are the many millions of species that are too small to see, such as the thousands of species of tiny, soil-dwelling creatures that recycle our wastes, or those in the sea that are onlyvisible with a microscope.
    The dazzling array of life-forms and the roles different species play in