On November 16, Sengor presented geological evidence for the setting and extent of the Permian extinction. He argued that the Permian extinction was not a global affair, as is widely believed, because most of the genera eliminated during the extinction lived in niches around the Palaeo-Tethys Ocean. Because of the equatorial location of this largely land-locked ocean, its internal circulation stopped and the ocean waters turned anoxic. At some point, ocean turnover led to the release of toxic gases (e.g., hydrogen sulfide), which killed not only the marine biota but also the land biota and the insects that lived within a 2000-kilometer-wide killing zone around the ocean margin.