has the precise properties of the hemoglobin molecule found in the human being. To test that number of combinations one after the other to find the one would, as you probably rightly suspect, take time. But given enough time, enough scientists, enough generations of scientists, surely trial and error would come through with the answer, inevitably, at long, long last. But exactly how much space and time would be required?
In order to answer that question we must first, get an idea of the size of the hemoglobin number. It seems awfully big, so we'll begin by taking something grandiose as a comparison. For instance, how does the hemoglobin number compare with the total number of molecules of hemoglobin on Earth? That's a fair beginning.
The human population of the Earth is 2,500,000,000 or, exponentially, 2.5 x 109. The average human being, including men, women and children, weighs, let us say, one hundred twenty pounds, which is equal to 5.5 x 104 grams. (There are 454 grams in a pound.) The total number of grams of living human flesh, blood, and bone on Earth is, therefore, about 1.4 x 1014 grams.
Seven per cent of the human body is blood so that the total amount of blood on Earth is 9.0 x 109 liters. (Since a liter is equal to about 1.06 quarts, that figure comes to nine and a half billion quarts.) Every liter of blood contains five trillion (5 x 1012) red cells, so the total number of human red cells on Earth is, therefore, 4.5 x 1022.
Although the red cell is microscopic in size, there is still enough room in each red cell for nearly three hundred million hemoglobin molecules—2.7 x 108, to be more precise. There are thus, on all the Earth, 1031 human hemoglobin molecules.
But those are the hemoglobin molecules belonging to human beings only. Other vertebrates, from whales to shrews, also possess hemoglobin in their blood, as do some lower forms of fife. Let's be generous and assume that for every human hemoglobin molecule on Earth there are one billion (109) nonhuman hemoglobin molecules. In that case, the total number of hemoglobin molecules on Earth, human and nonhuman, is 1040.
Even this number, unfortunately, is nowhere near the hemoglobin number and so it will not serve as a comparison.
Let us bring in the element of time and see if that helps us out. The average red blood cell has a life expectancy of about one third of a year. After that it is broken up and a new red blood cell takes its place. Let us suppose that every time a new red blood cell is formed, it contains a completely new set of hemoglobin molecules. In one year, then, a total of 3 x 1040 hemoglobin molecules will have existed. But the Earth has existed in solid state for something like three and a third billion years—3.3 x 109. Suppose
Hemoglobin and the Universe
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