Steve Benner: I'd like to get you to play a game. It's called the dialectic game, and the rules are that you must take a widely accepted conclusion, based on facts, and build an argument that draws the opposite conclusion. You're not going to be allowed to deny the facts, although you can certainly add more facts to the ones that are presented to you.

The game is designed to manage the natural propensity of the human mind to accept without question what is familiar to it. This game is useful throughout science, and it's absolutely essential to the topic of "life as we don't know it."

So let's see if we can play the game. The widely accepted conclusion is that water is uniquely ideal as a solvent for life. The dialectic game requires that you come up with a contrary proposition and generate facts that support it. So the contrary proposition is that water is NOT uniquely ideal as a solvent for life.

So now the question is, can we support that? If you play this game for about ten minutes, you'll be convinced that almost everything that you know about water, at least as the basis for life, is on shaky grounds.

Who has heard that water is uniquely ideal as a biosolvent because it floats when it freezes? Of course, the dialectical position is that water is not uniquely ideal as a biosolvent because it floats when it freezes. And now your goal is to come up with some reason why freezing and floating is a bad thing for life, when everybody else assumes it's a good thing for life.

The reason why it's good for life, or so the argument goes, is because when a body of water freezes, the ice floats to the surface and therefore insulates the body of water from further freezing. But when ice floats on the surface, it's white. This increases the albedo of an environment, enhancing freezing. That will cause less energy to be absorbed by a planet, and you have runaway glaciations and ice ages -- not good for life. Actually, for a stable global climate, we would want a majority solvent that damps the perturbation to climate, not one that amplifies it. You might want black ice that floats. Or ice that sinks rather than floats.

You could also use this dialectic game to manage Earth-o-centricity. What do you mean, ice floats? Well, Ice 1 floats. In a phase diagram for water, we can see that Ice 1 is just a tiny sliver of the different phases of frozen water. The other forms of ice are Ice 2, Ice 3, Ice 4, Ice 5, Ice 6, and so on. They all sink. So why do you think that ice floats? Because you live on Earth, where Ice 1 forms and floats at pressures that are common on Earth.

We can go further. How many people have heard that water is a great biosolvent because it has a large liquid range? Water stays liquid at temperatures ranging from zero to a hundred. So what is the range of liquid water on Mars? Well, there isn't any range of liquid water on Mars, because at the martian atmospheric pressure, ice sublimes before it melts. Why do you think that water has a large liquid range? Because you're born on Earth, and most of you live under approximately one atmosphere of pressure.

Of course, the area around a star where a planet's surface can have liquid water is quite small. So, in point of fact, liquid water is not very abundant in the cosmos.

But maybe water is still uniquely suited as a biosolvent because it dissolves many things. Well, many solvents dissolve many things. Formamide, my favorite solvent, also dissolves many things. So does ammonia. Sulfuric acid dissolves many things. Try it sometime. It will dissolve your finger.

You say, ah, water is uniquely suited because it dissolves DNA or RNA. But many of the bonds in RNA fall apart spontaneously when you place RNA in water. But that gives us a big problem for the origin of life.

Today, in your body after billions of years of evolution, you have evolved to repair the damage that water does to your DNA. But getting the DNA or RNA to assemble in water pre-biotically, where you don't have advanced repair systems, gives you what's called the water problem for the origin of life. We can't put the stuff together in water!

This is why chemists do not use water much as a solvent when we try to assemble molecules in the laboratory. We use other solvents because they aren't reactive, they don't participate in the reactions, therefore we can control what's going on.

Take my favorite solvent: formamide. Water is made of two hydrogen atoms and an atom of oxygen. Formamide also has two Hs and an O, plus there's an atom of carbon and hydrogen between the two. While water's liquid range on Earth goes from zero degrees Celsius to a hundred, formamide's is 3 to 210 C on Earth at one atmosphere of pressure. On Mars, the liquid range of formamide is zero to a hundred. I don't know why we don't believe that the gullies on Mars are carved by liquid formamide; there certainly is the possibility to have liquid formamide on Mars.

Formamide basically dissolves everything that water does. Formamide ice happens to sink. But by terms of liquid range on Earth and liquid range on Mars, formamide is better than water. In terms of solubility properties, they're the same. Whether it's better to have ice that floats or sinks, that's your call. Water is more abundant as a molecular species, although not in its liquid form.

Another argument for water? Well, water has a hydrophobic effect. Who has heard that as the ideal thing? Well, formamide has a hydrophobic effect; lots of solvents do. In fact, even ethane on Titan has a hydrophobic effect, in the sense that water is excluded from it and forms a separate phase.

So the next time you hear that water is uniquely suited as a biosolvent, how will you respond? You'll play the dialectic game. And if water is not uniquely optimal as a biosolvent, and if life is indisputably found in water, then, the thought arises: What other solvents might be appropriate to support life? Formamide? ethane? supercritical hydrogen-helium mixtures? Ammonia? Dinitrogen? Or sulfuric acid? When you go to a different solvent, you're into truly something different and weird.

I might be able to make a coherent argument for water as a uniquely ideal biosolvent, but it's not trivial to do so. One really needs to go to second generation ideas about the kinds of chemistry that could support evolution, and how they would interact with the solvent, before you can come up with some sort of argument that makes water better than other solvents.

Read Part 1 of the debate here

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