Leave organic sediments on the seafloor for 80 million years, and they might turn into crude oil. But some microbiologists and geobiologists aren't willing to wait that long to exploit the sediments' latent energy. They're developing a simple, inexpensive fuel cell-just two disk-shaped electrodes and a connecting circuit-that generates electricity when planted in bottom-of-the-ocean muck. "The seafloor constitutes a ready-made battery," says the Naval Research Laboratory's Leonard Tender, who coinvented the device with Clare Reimers of Oregon State University.

The marine sediment along continental coasts is about two percent organic carbon, mostly from dead plankton. Microbes ingest and oxidize the carbon, transferring sheared-off electrons to chemicals in the sediment. The transfer creates a voltage between the ocean bottom and the overlying seawater, a potential difference that generates a current when one electrode placed in the muck is joined together with another above it. Such devices, tested off the New Jersey and Oregon coastlines, have generated steady low-level power for nine months at a stretch. "Every indication is that they would have run forever," says Tender.