2,5-Dimethylfuran from approximately 2.7 x 10-year-old Rupemba-Belingwe stromatolite, Rhodesia: Potential evidence for remnants of carbohydrates.

2,5-Dimethylfuran, 2-methylfuran, and C(9)-C(20)n-alkanes have been isolated from the kerogen of a Rupemba stromatolite. These furans could be the oldest known stable remnants of biological carbohydrates if it is possible to prove that their progenitors are as old as the rock. Experiments showed that it is improbable that these compounds are analytical artifacts or laboratory contaminations. Postdepositional contaminations caused by fluids flowing through the rocks seem doubtful because of minimal permeability, which is supported by petrographic observations. Contamination by diffusion also appears to be unlikely. Because the rock had a mild temperature history, these molecules could have survived since Archean time. Because of all the evidence, the furans and alkanes are quite likely biochemical fossils.