The Thin Layer of Life

The earth still seems pretty big to most people. It measures some 25,000 miles at its circumference and its atmosphere stretches out some 600 miles into space. In the opposite direction, the immense oceans have trenches that go as deep as seven miles.

True. But actually we and the other living creatures and plants all live in what may be described as a very thin “envelope” girdling the earth. That thin “envelope” is called the “biosphere” because within it is found all earthly life known.

Calling it “very thin” is no exaggeration. Aside from a few floating spores and bacteria, life exists only within the first five miles of earth’s six-hundred-mile atmosphere. Actually, the far greater number of air-breathing things​—humans, animals, birds and plant life—​live within just the first ten thousand feet above sea level.

So, too, some life is found seven miles down on the ocean floors. But the vast majority of marine life exists in just the upper five hundred feet of the oceans. More than that, it is mainly concentrated along the “continental shelves,” the shallower waters bordering the continents, as well as similar waters around islands.

The biosphere, then, is a twelve-mile life zone around the globe. Thin, indeed. But in reality, fully 95 percent of all life on earth is found in a far thinner layer less than two miles thick. Within that remarkably thin “envelope” circulate air and water that are used over and over again by earth’s living things.

[Diagram on page 5]

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Almost all air-breathing things live within the first ten thousand feet above sea level. Most marine life exists in just the upper five hundred feet of the oceans

10,000 FEET

ZONE OF LIFE

SEA LEVEL

−500 FEET