A contemporary meal on Jurassic coal
Deep beneath the Surxondaryo Region of southern Uzbekistan, vast seams of Jurassic coal are slowly being consumed. The coal itself, formed from plant matter that died during the age of dinosaurs, is not the focus. Instead, the focus is on what is eating it: a community of microbes that are actively producing enormous quantities of natural gas. This is coal bed methane, but with a twist. Standard geological processes, involving heat and pressure over millions of years, typically create "thermogenic" methane. The gas in the Surxondaryo Basin is different; it is "biogenic," a waste product of microorganisms metabolizing ancient carbon in the permanent darkness of the subsurface.
The proof of this modern-day gas factory comes from isotopic analysis. Methane is a simple molecule (CH₄), but the carbon and hydrogen atoms within it can have different numbers of neutrons, creating isotopes. Methane produced by heat and pressure has a distinct isotopic signature compared to methane produced by life. Scientists analyze the ratio of carbon-13 to carbon-12 (expressed as δ¹³C). The δ¹³C values for the Surxondaryo methane are significantly "lighter"—more negative—than those of typical thermogenic gas, pointing squarely to a biological origin. This indicates that the gas is not from the Jurassic period but is being generated continuously in the present.