Consider for a moment the diagram above, from an article in the May 23, 2008, issue of Science called "The Microbial Engines That Drive Earth's Biogeochemical Cycles," by Paul Falkowski, Tom Fenchel and Edward Delong (click to enlarge). Here is the abstract of the article:
Virtually all nonequilibrium electron transfers on Earth are driven by a set of nanobiological machines composed largely of multimeric protein complexes associated with a small number of prosthetic groups. These machines evolved exclusively in microbes early in our planet's history yet, despite their antiquity, are highly conserved. Hence, although there is enormous genetic diversity in nature, there remains a relatively stable set of core genes coding for the major redox reactions essential for life and biogeochemical cycles. These genes created and coevolved with biogeochemical cycles and were passed from microbe to microbe primarily by horizontal gene transfer. A major challenge in the coming decades is to understand how these machines evolved, how they work, and the processes that control their activity on both molecular and planetary scales.Don't be put off by the technical language. The authors are describing an unseen microbial world of almost unimaginable dimension -- bacteria, yeasts, fungi, and archaea -- that live in places as diverse as the human gut and the bottom of the sea, cycling and recycling the material stuff of life. The diagram depicts the global, interconnected network of the microbial-mediated cycles for hydrogen, carbon, nitrogen, oxygen, sulfur and iron, the principle elements on which all living things depend. This world of unseen organisms drives some of the largest scale phenomena on the planet, including photosynthesis, nitrogen cycling, and pandemics of infectious disease. Understanding how these systems work is key to dealing with such issues as climate change, energy shortages, and food production.
It is wonderful enough to realize how our very existence, and that of human civilization, depends upon an unseen universe of "bugs." Wonderful too to see some of these reactions displayed in a diagram of such intrinsic beauty -- like a painting by Mondrian.