In the 1990s, there was much speculation about terraforming planets, particularly Mars. The idea was that the planet could be converted into something like Earth. To make Mars roughly like Earth, the temperature has to be raised by about ninety Centigrade degrees, atmospheric pressure has to be raised by something approaching a hundred times present pressure, and a lot of water must be found. That presumably comes from buried ice, so besides uncovering it, an enormous amount of heat is required to melt it. The reason Mars is colder is that the sun delivers half the power to Mars than Earth, due to Mars being further away. The gas pressure depends on two things. The first is there has to be enough material, and the second is we have to get it into the gas phase. The most obvious gas is carbon dioxide, because as dry ice, it could be in the solid state, but would be amenable to heating. The problem is, if carbon dioxide is present with a lot of water, it will be absorbed by the water, particularly cold water, and slowly turned into material like dolomite. Nitrogen is the major gas in our atmosphere, but that would be a gas on Mars, and there is very little in the Martian atmosphere.
Why did anyone ever think Terraforming was possible? One reason may be that about 3.6 Gy ago (a gigayear is a thousand million years) it was thought that there were huge rivers on Mars. The Viking images found a huge number of massive river valleys, and so it was thought there had to be sufficient temperatures to melt the water. Subsequent information has suggested that these rivers did not persist over a prolonged wet period, but rather there were intermittent periods where significant flows occurred. Such rivers probably never flowed for more than a million years or so, and while a million years might seem to be an extremely long period to us, it is trivial in the life of the solar system. Nevertheless the rivers meandered for that period, which is at least suggestive that they were relatively stable for that time, so what went wrong?
When I wrote Red Gold, I needed the major protagonist to make an unexpected discovery to expose a fraud, and it was then that I had an idea. The average temperature on Mars now is -80 degrees C, and while we could imagine some sort of greenhouse effect warming the early Mars, the sun only emitted about two-thirds the energy it does now, so temperature would have been a more severe problem. To me, it was inconceivable that the temperature could get sufficiently above the melting point of ice to give significant flows, but there is one way to make water liquid at -80 degrees C, and that is to have ammonia present. If the volcanoes gave off ammonia as well as water, that would give some greenhouse gas, and the carbon would be present as methane, this being what is called a reducing atmosphere. Sunlight tends to act with water to oxidize things, giving off hydrogen that escapes to space. This has happened extensively on Mars, indeed at many sites where chloride has been deposited on the surface, it has been converted to perchlorate. So methane would oxidize to carbon dioxide, and carbon dioxide would react with ammonia to make first, ammonium carbonate, then, given heat or time, urea. So my “unexpected discovery” was the fertilizer that would make the settlement of Mars possible. I had something that I thought would make my plot plausible.
Funnily enough, this thought took on a life of its own; the more I thought about it, the more I liked it, because it helps to explain, amongst other things, how life began. (The reduced form of nitrogen is a set of compound called nitrides. Water on nitrides, plus heat, makes ammonia, and also cyanide, which is effectively carbon nitride.) Standard theory, of course, assumes that nitrogen was always emitted as the nitrogen gas we have in our atmosphere. Of course you might think that all the scientists are right and I am wrong. Amongst others, Carl Sagan calculated that if ammonia was emitted into the atmosphere, it would be removed by sunlight in a matter of a decade or so, and he had to be right, surely? Well, no. Anyone can be wrong. (Of course you may say some, such as me, are more likely to be wrong than others!) However, in this case I maintain that Sagan was wrong because he overlooked something: ammonia dissolves in water at a very fast rate, and in water it will be protected to some extent. To justify that, we have found rocks on Earth that are 3.2 billion years old and that have samples of seawater enclosed, and these drops of seawater have very high levels of ammonia. These levels are sufficiently high that about 10% of Earth’s nitrogen must have been dissolved in the sea as ammonia at the time, and that is after the Earth had been around for about 500 million years after the water flowed on Mars.
If anyone is interested in why I think this occurred, Red Gold has an appendix where my first explanation is given in simple language. For those who want something a bit more detailed, together with a review of several hundred scientific papers, you could try my ebook, Planetary Formation and Biogenesis.