The gates to hell in antiquity and their relation to geogenic CO₂ emissions

In Greek mythology, the netherworld is guarded by the three-headed hellhound Kerberos. For persons that passed away it was rather easy to find their way down to the realms of the shadows. Yet, there was no escape from the world of Hades. The gates to hell were used by the souls of the deceased but also by diseased people seeking cure or even prophecies. In ancient times, these gates to the abyss were always connected to unexplainable geo-biological phenomena. Vapors, deadly gases, darkness in caves, bubbling springs, and creeks changing their color were such places. In addition, localities where animals showed strange behavior or plant growth was irregular were selected for sanctuaries, oracles, or gates to the Hadean. Rather often but not always, the geogenic gas carbon dioxide plays a decisive role at these entrances, as it is colorless and tasteless but kills all aerobic life quite quickly at higher concentrations.