MAXIMUM NUMBER OF CELLS ON EARTH

It may be useful to consider how many living things this planet can accommodate. An earlier calculation showed that about 10 billion plant or animal cells can fit into one cubic inch. Let's now cover the entire globe, including all land and water, with such living cells to a thickness of 15 feet. The whole earth, everywhere you looked, would be a teeming mass of living cells, with no space between any of them.

We calculated the number of square inches on the earth as 7.87 x 10¹⁷. If we go to a depth of 15 feet, then the total amount of cubic inches is this number multiplied by 180, or 1.4 x 10²⁰. Multiply all these cubic inches by ten billion, the number of cells that fit into one cubic inch, and we get 1.4 x 10³⁰ cells in total. Although in the ocean life can exist at great depths, and thus the oceans may conceivably have a totality of living things in it that would go beyond the measure of a thickness of fifteen feet that I am using, in reality, probably no place on earth is ever packed solid with living things. Thus, I believe that it is safe to say that the earth has never had on it more than this number of plant and animals cells at any single moment.

Needless to say, the number of bacterial cells that the earth could accommodate is much much larger. As much as one quadrillion of the smallest bacteria would fit into one cubic inch. This is one million times as many as the plant or animal cells we used in our calculation. The globe, packed with these sort of cells to the same thickness as before, could accommodate 10³⁶ cells. It is surely safe to say that this is the upper limit for the number of cells, of any sort, that the earth has ever contained at one point in time.