The trouble with ecology is that you never know where to start because everything affects everything else. An unseasonal freeze in Texas can affect the price of breakfast in Alaska and that can affect the salmon catch and that can affect something else. Or take the old history book case: the English colonies took England's young bachelors and that meant old maids at home and old maids keep cats and the cats catch field mice and the field mice destroy the bumble bee nests and bumble bees are necessary to clover and cattle eat clover and cattle furnish the roast beef of old England to feed the soldiers to protect the colonies that the bachelors emigrated to, which caused the old maids.
Not very scientific, is it? I mean you have too many variables and you can't put figures to them. George says that if you can't take a measurement and write it down in figures you don't know enough about a thing to call what you are doing with it "science" and, as for him, hell stick to straight engineering, thank you.
But there were some clear cut things about applied ecology on Ganymede which you could get your teeth into. Insects, for instance—on Ganymede, under no circumstances do you step on an insect. There were no insects on Ganymede when men first landed there. Any insects there now are there because the bionomics board planned it that way and the chief ecologist okayed the invasion. He wants that insect to stay right where it is, doing whatever it is that insects do; he wants it to wax and grow fat and raise lots of little insects.
Of course a Scout doesn't go out of his way to step on anything but black widow spiders and the like, anyhow—but it really brings it up to the top of your mind to know that stepping on an insect carries with it a stiff fine if you are caught, as well as a very pointed lecture telling you that the colony can get along very nicely without you but the insects are necessary.
Or take earthworms. I know they are worth their weight in uranium because I was buying them before I was through. A farmer can't get along without earthworms.
Introducing insects to a planet isn't as easy as it sounds. Noah had less trouble with his animals, two by two, because when the waters went away he still had a planet that was suited to his load. Ganymede isn't Earth. Take bees—we brought bees in the Mayflower but we didn't turn them loose; they were all in the shed called "Oahu" and likely to stay there for a smart spell. Bees need clover, or a reasonable facsimile. Clover would grow on Ganymede but our real use for clover was to fix nitrogen in the soil and thereby refresh a worn out field. We weren't planting clover yet because there wasn't any nitrogen in the air to fix—or not much.
But I am ahead of my story. This takes us into the engineering side of ecology. Ganymede was bare rock and ice before we came along, cold as could be, and no atmosphere to speak of—just traces of ammonia and methane. So the first thing to do was to give it an atmosphere men could breathe.
The material was there—ice. Apply enough power, bust up the water molecule into hydrogen and oxygen. The hydrogen goes up—naturally—and the oxygen sits on the surface where you can breathe it. That went on for more than fifty years.
Any idea how much power it takes to give a planet the size of Ganymede three pressure-pounds of oxygen all over its surface?
Three pressure-pounds per square inch means nine mass pounds, because Ganymede has only one third the surface gravitation of Earth. That means you have to start with nine pounds of ice for every square inch of Ganymede—and that ice is cold to start with, better than two hundred degrees below zero Fahrenheit
First you warm it to die freezing point, then you melt it, then you dissociate the water molecule into oxygen and hydrogen—not in the ordinary laboratory way by electrolysis, but by extreme heat in a mass converter. The result is three pressure pounds of oxygen and hydrogen mix for that square inch. It's not an explosive mixture, because the hydrogen, being light, sits on top and the boundary layer is too near to being a vacuum to maintain burning.
But to carry out this breakdown takes power and plenty of it—65,000 Btus for each square inch of surface, or for each nine pounds of ice, whichever way you like it. That adds up; Ganymede may be a small planet but it has 135,000,000,000,000,000 square inches of surface. Multiply that by 65,000 Btus for each square inch, then convert British thermal units to ergs and you get:
92,500,000,000,000,000,000,000,000,000,000 ergs.
Ninety-two-and-a-half million billon quadrillion ergs! That figure is such a beauty that I wrote it down in my diary and showed it to George.
He wasn't impressed. George said that all figures were the same size and nobody but a dimwit is impressed by strings of zeroes. He made me work out what the figure meant in terms of mass-energy, by the good old E = MC2 formula, since mass-energy converters were used to give Ganymede its atmosphere.
By Einstein's law, one gram mass equals 9x1020 ergs, so that fancy long figure works out to be 1.03x1011 grams of energy, or 113,200 tons. It was ice, mostly, that they converted into energy, some of the same ice that was being turned into atmosphere—though probably some country rock crept in along with the ice. A mass converter will eat anything.
Let's say it was all ice; that amounts to a cube of ice a hundred and sixty feet on an edge. That was a number I felt I could understand.
I showed my answer to George and he still was not impressed. He said I ought to be able to understand one figure just as easily as the other, that both meant the same thing, and both figures were the same size.
Don't get the idea that Ganymede's atmosphere was made from a cube of ice 160 feet on a side; that was just the mass which had to be converted to energy to turn the trick. The mass of ice which was changed to oxygen and hydrogen would, if converted back into ice, cover the entire planet more than twenty feet deep —like the ice cap that used to cover Greenland.
George says all that proves is that there was a lot of ice on Ganymede to start with and that if we hadn't had mass converters we could never have colonized it. Sometimes I think engineers get so matter of fact that they miss a lot of the juice in life.
With three pressure-pounds of oxygen on Ganymede and the heat trap in place and the place warmed up so that blood wouldn't freeze in your veins colonists could move in and move around without wearing space suits and without living in pressure chambers. The atmosphere project didn't stop, however. In the first place, since Ganymede has a low escape speed, only 1.8 miles per second compared with Earth's 7 m/s, the new atmosphere would gradually bleed off to outer space, especially the hydrogen, and would be lost— in a million years or so. In the second place, nitrogen was needed.
We don't need nitrogen to breathe and ordinarily we don't think much about it. But it takes nitrogen to make protein—muscle. Most plants take it out of the ground; some plants, like clover and alfalfa and beans, take it out of the air as well and put it back into the ground. Ganymede's soil was rich in nitrogen; the original scanty atmosphere was partly ammonia—but the day would come when we would have to put the nitrogen back in that we were taking out. So the atmosphere project was now turned to making nitrogen.
This wasn't as simple as breaking up water; it called for converting stable isotope oxygen-16 into stable isotope nitrogen-14, an energy consuming reaction probably impossible in nature—or so the book said—and long considered theoretically impossible. I hadn't had any nucleonics beyond high school physics, so I skipped the equations. The real point was, it could be done, in the proper sort of a mass-energy converter, and Ganymede would have nitrogen in her atmosphere by the time her fields were exhausted and had to be replenished.