Final answer:
At high altitudes, such as advanced base camps on mountains like Everest, the 'air is so thin' meaning there's not enough oxygen and atmospheric pressure for normal breathing and physical exertion, risking altitude sickness and hypoxia.
Step-by-step explanation:
At advanced base camp, the phrase "air is so thin" typically refers to the low levels of oxygen and low barometric pressure present at high altitudes, which can make certain activities such as breathing and physical exertion extremely difficult or even impossible. This is a challenge because the human respiratory system is designed to function within certain ranges of oxygen concentration and atmospheric pressure.
At elevations such as those found in mountainous regions, these conditions are no longer met, and the body can struggle to obtain the oxygen it requires. Mountain climbers, like those on Mount Everest, often face harsh conditions that can lead to altitude sickness, hypoxia (lack of oxygen), and other life-threatening conditions without proper acclimatization and supplemental oxygen.