mountain mid-elevation mountain https://orcid.org/0000-0002-7556-2097 On Earth, mountains in this category are below the atmospheric oxycline above which oxygen concentrations fall below the physiological tolerance threshold of most humans. Note that the threshold elevations are inconsistent between the various reports which list this classification: while some have overlapping thresholds, others are non-overlapping. The latter model is used in ENVO for coherence and to adhere to the Kapos et al. 2000 reference. A mountain which has a maximum elevation between 300 and 2499 metres above sea level and slopes greater than or equal to two degrees of inclination.