Researchers have developed ways to reclaim mining sites by conservation methods and recycling. Techniques used for extraction of minerals from low-grade ore can be adapted to detoxify contaminated soils as well as water. And mining practices in use now, such as surface landscaping and sealing mine walls to reduce seepage through the mine into the water table, have successfully minimized environmental modification. Incorporating the traditional practice of backfilling spent caverns with tailings to prevent subsidence, modern reclamation efforts strive to recreate the original scene as closely as possible.

Recovery of petroleum resources also can threaten the environment. Oil spills come to mind—the Exxon Valdez spill and the oil spill released into the Persian Gulf during the fighting to reinstate the status quo of the Kuwaiti Emirate. But petroleum geologists are proud of their efforts to reduce the dangers of spillage during the production phase. Today, oil lost to the environment during production is much less than the amount released naturally through seepage. The greatest dangers from oil spillage are found in the transportation phase—and tanker transportation is the most dangerous of all.

The burning of coal produces emissions that accelerate global warming trends. Nuclear energy creates radioactive by-products that can threaten the environment in a variety of ways—as emission into the atmosphere or invasion into the groundwater. Even burning wood causes smog. But nature does have the ability to absorb some of this abuse—it has a carrying capacity. The carrying capacity is the upper limit of a system's ability to support all components within the bounds of available resources. When the carrying capacity is exceeded, a threshold is crossed, and new equilibria establish themselves. Often a new equilibrium spells disaster for the components supported by the former system. For living beings crossing such a threshold can mean extinction.

The carrying capacity of a natural system may be threatened by various means. Natural climatic changes can devastate landscapes and destroy soils just as efficiently as humans can in their roles of gatherer, farmer, or skyscraper builder. Thresholds of stress are crossed whenever a natural disaster hits—earthquakes, volcanoes, and floods all result from natural systems thrown into a different order. Seismologists, volcanologists, and hydrologists experiment and observe, in search of greater understanding of the natural systems, their carrying capacities, and their dangerous thresholds. That understanding should result in the ability to predict the potential for problems, and such predictions might permit mitigation of the intensity of an event—or at least provide time to warn populations to evacuate endangered regions and thus save lives.

The humans who occupy this planet are profoundly dependent on the ordered operation of its natural systems. Human populations exploit the minerals, fuels, soils, and waters, straining against capacities and adapting to limits. That straining and adapting is what characterize life: it's completely natural—as extinction will be, if the human species strains too hard or adapts too slowly.



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