Search for Intraterrestrial Life Scores Big
Single-celled organisms may be tiny, but what they lack in bulk they make up for in volume and importance. Scientists have been appreciating more than ever the ubiquitous presence of microbes on our planet and the roles they play to sustain the biosphere.
PhysOrg reported that half of the world’s life may lie below the land and sea. Scientists at UC Santa Cruz are thinking earth’s “habitable zone” may extend much deeper than previously thought: to depths of hundreds or thousands of meters. Microbes inhabit subsurface aquifers that could contain more water than all the rivers on earth. The search for ET begins at home, they think: “Scientists say research on ‘intraterrestrial life’ complements astronomers’ hunt for ‘extraterrestrial life’ around other stars and planets,” the article said.
Of course, all life we know on earth uses the same genetic coding and translation system. But the vast bulk of life on our planet may never see the sun, and some of it does not even need oxygen. “Diving for Microbes,” an article in Caltech’s Engineering and Science magazine (LXXIII:1, 2010) discussed work to understand the microbes on the seafloor that digest methane and support entire ecosystems in the dark. In passing, author Marcus Y. Woo gave some “wow factor” information about microbes in general:
Scientists estimate that the planet has 5 x 1030 microorganisms—that’s more than a hundred million times the number of stars in the observable universe. Scoop up all these little critters together, and they’ll weigh several hundred billion metric tons, a mass about a thousand times greater than that of all the people on Earth. The majority of the planet’s microbes are believed to live inside Earth’s crust or just below the seafloor, regions that are scarcely understood and explored, so many more bug-based ecosystems are likely still undiscovered.
Often unjustly maligned, microbes are essential for life. “They are an integral part of almost every facet of our planet,” [Victoria] Orphan [Assistant Professor of Geobiology, Caltech] says. No species of archaea are known to cause diseases, and only a small fraction of bacteria do; most are harmless or even helpful. Bacteria help digestion, and, as biologists are finding, they play essential roles in our immune systems and overall health….
(For more on microbes aiding digestion, see this recent article on PhysOrg. An article on Science Daily noted that there are more microbe genes in your gut than human genes for your body; so did the BBC News, that said your microbe passengers constitute a “second genome” of yours.)
What scientists are finding, therefore, is not only that we depend on microbes, which outnumber our own cells 10 to 1 as we live and move, but that they are essential for the habitability of the entire planet. The methane-eating bacteria on the seafloor, Orphan’s team found, play a huge role in earth’s nitrogen cycle. They are among the only life forms capable of “fixing” nitrogen from atmospheric nitrogen gas and making it available for use by other organisms. “Without these microbes, the planet would run out of biologically available nitrogen in less than a month,” the article said.
Realizations like this are stimulating a flourishing field of “geobiology” – the study of relationships between life and the earth. One member of the Caltech team commented, “If all bacteria and archaea just stopped functioning, life on Earth would come to an abrupt halt.” Microbes are key players in earth’s nutrient cycles. Dr. Orphan added, “…every fifth breath you take, thank a microbe.”
Since we depend on microbes so much, why not let them become our teachers? Another article on PhysOrg reported about scientists seeking better ways to convert carbon dioxide into carbon monoxide, using sunlight. They asked, “WWND? What would nature do?” They don’t have a particular microbe in mind that does this task, but realized that thinking like a microbe might provide a fruitful way to approach the problem. An Oxford scientist commented, “We looked for a way that seems like nature’s way of doing it, which is more efficient.”
Update 03/19/2010: Scientists at Michigan State found that microbes are important for promoting biodiversity and cleaning the environment, reported PhysOrg. Because many of them can live for long periods in a dormant state, they can hold out in unfavorable conditions and respond to environmental cues. “Microbes are the most abundant and diverse organisms on earth; they carry out essential ecosystem services,” said one of the scientists. “Among these services are contaminant degradation, carbon sequestration and various processes that affect plant productivity.”
Are you really an “individual”? Yes and no; you couldn’t live without your contingent of microbes constantly at your service. We are beginning to see biology as hierarchies of interrelated systems. Who would have thought that our health depends on microbes digesting methane seeping out of the deep ocean? Who would have thought that the air we breathe and the plants we consume owe their existence to hundreds of billions of metric tons of organisms too small to see? Who would have thought that channels deep under the crust and ocean are thriving habitats for life? Earth’s biosphere is a system of systems of systems – each of them showcasing intelligent design at all levels.
Unfortunately, some of the articles spoiled their otherwise good content with evolutionary non-sequiturs. They told us that SITI is a first step to SETI – finding intraterrestrial life helps the search for extraterrestrial life. That’s like saying finding a library in a large city will help locate libraries on Mars. They told us that microbes were around billions of years before humans arrived – an unsupported assertion. They told us that since microbes can digest methane on Earth, they might be digesting it on Titan. Such statements serve little more than to restate reigning dogmas. Learn to keep them separate from the observational facts, and you can still enjoy scientific articles.