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Science Frontiers ONLINE No. 57: May-Jun 1988 |
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Living stalactites! subterranean life! (in three parts)
Translation of the Introduction of an article from Science et Vie:
"One has always held that the calcareous concretions in caves are the work of water and the chemical constituents of the rock. Surprise! The true workers in the kingdom of darkness are living organisms."
It's all true. All the references we have state unequivocally that stalactites and stalagmites are created by dripping water that is charged with minerals, calcium carbonate in particular.
That stalactites contain crystals of calcite is not denied in the Science et Vie article. Indeed, an electron micro scope photograph shows them clearly; but it also shows that a web of mineralized bacteria is also an intergral part of the stalactite's structure. Laboratory simulations have shown that microorganisms take an active role in the process of mineralization. (Dupont, George; "Et Si les Stalactites Etaient Vivantes?" Science et Vie, p. 86, August 1987. Cr. C. Mauge.)
Besides being a surprising adjustment of our ideas about stalactite growth, the recognition that microorganisms may play an active role in the subterranean world stimulates two new questions: (1) Can we believe any longer that stalactite size is a measure of age, as is often claimed? (2) Is the immense network of known caves (some as long as 500 kilometers) the consequence only of chemical actions?
It turns out that the earth beneath our feet is not so solid after all. Some 40,000 caves are known in the United States alone. There are thought to be ten times that number that have no surface openings and therefore escape spelunking census takers. And besides caves big enough for humans to crawl into, there exists an immensely greater continuum of cracks, crevices, channels, and pores which circulate air, water, and chemicals in solution. This "crevicular structure" may be continuous for thousands of miles, possibly around the world. Furthermore, it is filled with life forms of great variety, usually blind, and usually related to creatures of the light. A recent article in American Scientist focuses on the evolution of the larger forms of subterranean life, especially the amphipods. Interestingly enough, it doesn't even mention micro-organisms.
(Holsinger, John R.; "Troglogbites: The Evolution of Cave-Dwelling Organisms," (American Scientist, 76:147, 1988.)
Comment. We have juxtaposed these two articles because together they underscore the great extent of the crevicular domain, the "kingdom of the darkness" of the French article, and also the fact that this crevicular realm teems with life forms, some of which are involved in its construction.