How thick is the earth’s atmosphere?

We know that the air is thinner on a mountain top and climbers of Mount Everest, which is in Asia, have to use extra oxygen supplies long before they reach the peak. There is a lot of other evidence to indicate that the air is thickest near the earth and gets thinner as we reach up to some high point where it finally merges with the nothingness of space.

When we speak of a thick fog, we mean a dense fog. Thick air also can mean dense air or air in which the particles are closely packed together. It is more accurate, however, to call this the density of air. When we speak of the thickness of the atmosphere, we usually mean the depth of earth' s blanket of air measured from the ground to a point high above our heads where the air ends and space begins.

The confusion between thickness and density is made even more confusing. In the earths atmosphere there is a definite relationship between the aims density and its depth. The top of the airy blanket may be about 1,000 miles above our heads, no one knows for sure. But half of the weight of this blanket is packed into a layer reaching from the earth to about three miles above it.

Atmospheric pressure is the weight of the air pressing down upon the earth. At sea level under normal conditions, standard air pressure 3s 14.7 pounds per square inch. This means that a one inch column of air reaching from the ground to the top of the atmosphere weighs 14.7 pounds. In a plane flying three miles high, the air pressure is about seven pounds per square inch. Almost three quarters of the weight or density of the atmosphere lies between the earth and six miles above it.

At 20 miles up, the air pressure is about 0.18 pounds. This is very thin air, far too thin for living conditions, and as we proceed higher it becomes even thinner. There is still air, however, at 100, 200 and even 500 miles, though the gaseous particles are becoming more widely separated. There are enough air particles at 600 miles to add a touch of glory to the dazzling northern lights. We do not know for certain, but there may be a few particles of air gases 1,000 miles above the earth,

There is a relationship, then, between the density  thickness and the depth thickness of the atmosphere. The problem is somewhat like cutting a piece of string in half, and in half again and again until the sections are too small to be seen. The atmosphere reaches up, getting thinner and thinner, and where it ends nobody knows.