The Oracle of Delphi was the place to go for guidance in ancient Greece. The oracle was believed to speak through the Pythia, an elderly priestess who would fall into a trance state and utter cryptic predictions about war, agriculture and other vital matters of the time. According to Plutarch (who served as the temple's high priest for a time) and other ancient authorities, gaseous emissions induced the Pythia's trance state. But after French archaeologists failed to find the famed vapors a century ago, that explanation was dismissed.

Now a new study, published in this month's issue of Geology, reveals that the purported trance-inducing gases may have been very real after all. Following up on the ancients' assertions that the gases rose from fissures in the bedrock, J. Z. de Boer of Wesleyan University and his colleagues located several young geologic faults that fit that description. The scientists say that hydrocarbon gases from bituminous limestone probably brought on the Pythia's trance. In fact, the team found ethane, methane and ethylene in spring water located near the oracle. Ethylene, which has served as anesthesia in the past, is known to produce euphoric effects similar to those described by Plutarch.