This collective refusal to accept the inevitability of death is not a simple thing. It is not the absence of despair — the accounts make clear that despair was present, that there were moments when individuals believed they were going to die, that the ongoing grief and exhaustion and hunger produced states of mind that were far from optimistic. It is something more specific: the choice, made repeatedly, to do the next thing that was required rather than the alternative of not doing it.
The sixteen survivors came home on December 23, 1972. They had been gone for 72 days. The world had declared them dead. They had disagreed.
## The Physics of Cold
One element of the survival story that is easy to state but difficult to fully appreciate is what cold at that altitude actually does to a human body over days and weeks.
The crash site sat at approximately 3,660 meters above sea level. This is an altitude roughly equivalent to the high peaks of the Colorado Rockies or the lower slopes of the Alps. At this elevation, the air contains approximately 65 percent of the oxygen present at sea level. For a person who has not acclimatized — and the crash survivors had not; they were tourists, not mountaineers — movement at this altitude is aerobically more demanding than the same movement at sea level. The heart and lungs work harder. Physical exertion produces more rapid exhaustion.
Temperature at this altitude in the southern Andes in October and November — the Southern Hemisphere spring — is cold by any standard and extreme by the standards of people wearing city clothing. Daytime temperatures in the valley might reach several degrees above zero in direct sunlight; nighttime temperatures dropped well below freezing. The wind that moved through the valley carried a chill factor that made the effective temperature considerably colder than the thermometer reading.