The biosphere

 The Biosphere

Reconnaissance missions to the planets of the inner solar system have revealed stark and barren landscapes. From the heavily cratered and atmosphere less surfaces of both Mercury and the Moon to the hot sulfurous fogs of Venus and the dusty, windswept surface of Mars, no sign of life is apparent anywhere. The biosphere, by definition the place where all Earth’s life dwells, is a delight with its green, wet contrast. Austrian geologist Eduard Suess invented the term biosphere to match the other envelopes of the planet: the atmosphere of gas; the hydrosphere of oceans, lakes, rivers, springs and other waters; and the lithosphere, or the solid rock surface of the outer portion of Earth. Yet it was the great Russian crystallographer and mineralogist Vladimir I. Vernadsky who brought the term into common parlance with his book of the same name. In The Biosphere (1926) Vernadsky outlines his view of life as a major geological force. Living matter, Vernadsky contends, erodes, levels, transports, and chemically transforms surface rocks, minerals, and other features of Earth. If the biosphere is the place where life is found, the biota (or the biomass as a whole) is the sum of all living forms: flora, fauna, and microbiota.

During the second half of the 20th century, study of the deep sea, the upper atmosphere, the Antarctic dry deserts, newly opened caves, sulfurous tunnels, and granitic rocks showed that Earth’s surface is vigorously inhabited in places that were unknown to Vernadsky and his colleagues. Vernadsky’s international school of thought ushered in the field of “biogeochemistry,” and chemists and geologists were recruited to consider life as a planetary phenomenon. But not until giant, mouthless, red-gilled tube worms were videographed in the late 1970s and ’80s did the extent and the weirdness of Earth’s biota begin to be fathomed. Entire large ecosystems were recognized on the ocean’s bottom that live not by the usual plant photosynthesis but rather by chemolithoautotrophy, a kind of metabolism in which organisms make food from carbon dioxide using energy from the oxidation of sulfide, methane, or other inorganic compounds. These discoveries have led to a deeper understanding of life’s varied modes of nutrition and sources of energy. Bacterial symbionts living in the tissues of some polychaete worms (alvinellids) or pogonophora (such as Riftia pacytila) provide the animals with their total nutritional needs. The submarine ecosystems supported by bacteria thrive along the worldwide rift zones that extend along the borders of huge continental plates at the Mid-Atlantic Ridge, on the East Pacific Rise, at 21° north of the Equator off the coast of Baja California, Mex., and at a dozen other newly studied sites. By the beginning of the 21st century it had become abundantly clear that many life-forms and ecosystems remained unknown or under-studied. Those in the Siberian tundra, in the thickly forested portions of the Amazon River valley and its tributaries, at the tops of remote mountains and inside granitic rocks in temperate zones, and in the Centre of Africa remain as inaccessible to most naturalists as they have been throughout history. The easily accessed woodlands and fields of well-lit land surfaces are another story.

On land, 24 percent of the productivity of organic carbon biomass generated by plants is directly controlled by burgeoning populations of one species, humans. As Vernadsky noted, life in general and human life in particular tend to accelerate the number of materials and the rate of flow of these materials through the biosphere, the place where all life exists—so far.