Petroleum deposits formed millions of years ago, when organic-rich sediments were buried and transformed under heat and pressure deep in the Earth’s crust. Most deposits remain deep in the Earth, making it expensive to drill for oil and gas. However, geologic uplift occasionally brings deposits back near the Earth’s surface.
Periodically, these are even known to leak oil and gas. The Biblical story of the burning bush is thought to derive from a petroleum deposit that ignited when it was leaking in the desert of Israel. Scientists estimate that about 5% of the methane – or natural gas – added to atmosphere comes from natural leaks in the Earth’s crust. Most of the rest stems from human activities.
Hydrocarbons also leak from petroleum deposits buried in marine sediments. Bizarre communities of marine organisms colonize these vents at the sea floor, where they metabolize energy-rich hydrocarbons. A new estimate suggests that each year natural hydrocarbon leakage in the Gulf of Mexico is between 14 and 120% of the leakage that occurred during the Deepwater Horizon Oil Spill.
Unlike a spill, natural leakage occurs at a variety of locations, making impacts diffuse. Most natural vents go unnoticed because microorganisms break down the oil before it reaches the water’s surface. Vents help explain how petroleum-degrading microbes, which proliferate after oil spills, persist in the environment. Perhaps these useful microbes can even be cultivated and kept in culture to use in response to future oil spills in remote marine locations.
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Web Links
See Smith, Flemings and Fulton. 2014. Hydrocarbon flux from natural deepwater Gulf of Mexico vents. Earth and Planetary Science Letters 395: 241-253.
Photo, taken April 25, 2010, courtesy of the NASA Goddard Space Flight Center via Flickr.
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Earth Wise is a production of WAMC Northeast Public Radio. Support for Earth Wise comes from the Cary Institute of Ecosystem Studies in Millbrook, NY.