Based on what we have seen of the rise of life on our planet, one can extrapolate that there are three basic needs for life to develop elsewhere in the universe. Only if all three of these things are present can life form, thrive and become diverse enough that it evolves to fill all the possible niches within its locally available volume.
First: an energy source. For us this is the sun. In the darkness at the bottom of the ocean this can be unstable sulfates constantly spewed from the ocean floor. In other places in the universe the energy may take a different form; but energy must be available, it must be abundant, and its availability must not be interrupted too thoroughly or for too long.
Second: complicated chemistry. There may be ways for life to form without chemistry but we have no proof of it as yet. All the life forms we have examined so far are chemical, and their chemistry is astoundingly complicated.
The third requirement is time; lots and lots of time. Time measured in many, many millions of years.
All three of these things must come together to allow for life to develop. If any one of them is lacking life is unlikely to form.
For this essay I would like to examine only one of these three. Time hardly needs any explanation; even the concept of an energy source is relatively straightforward; but complex chemistry has a billion possible permutations. Fortunately I will only talk about one: expediting it.
To expedite means to facilitate, to make something more efficient, more effective, or just plain faster. For complex chemistry solvents do exactly that. The solvent of choice on earth is of course water. The earth is positively awash in it.
But let's pause to define solvent. Solvents are liquids (usually, though sometimes they are dense gasses) which are capable of dissolving or absorbing one or more other chemical substances. To the eye, the dissolved substance magically disappears into the solvent. In reality it has been completely disassembled into its individual component molecules which are busily bouncing among the individual component molecules of the solvent.
By separating the dissolved substance into individual molecules the solvent gives the dissolved substance the opportunity for its molecules to mix and interact with the individual molecules of other dissolved substances, thus expediting their chemical reactions.
This is a powerfully useful situation, but there is no reason why the solvent must be water. Other liquids are common in this universe: ammonia, methane, hydrogen, even iron is a good solvent. It can dissolve huge quantities of carbon.
But while the solvent does not have to be water, it does have to remain liquid. If it freezes solid the substances dissolved in it are no longer free to mingle with other dissolved substances and can no longer undergo chemical reactions; in which case the expediting grinds to a halt.
In order to exist in a liquid state, a substance must be above its melting point and under enough pressure to keep it from boiling away. For most substances the amount of pressure needed for this is never zero. That is, in order to exist as a liquid, and therefore work as a solvent, the solvent must be under pressure. On earth the atmosphere provides the pressure; same on Jupiter and Saturn and the other gas giant planets. On some of the larger moons in this solar system, the outer crust provides the pressure to maintain oceans of liquid deep underground. When these liquids manage to squeeze up to the surface through a crack they instantly boil away to vapor because they are no longer under pressure.
Every ocean in this universe is under pressure, either from an atmosphere or from a thick covering of some kind of crust. And since atmospheres are tricky, finicky things for planets to produce and maintain, and crusts are easy—indeed, just about unavoidable—there will be far more oceans under crusts in this universe than under atmospheres. The ratio may be as much as a hundred to one.
With the recent discovery of so many hot Jupiters—planets with a mass similar to that of Jupiter but orbiting so close to their star that their planetary surface temperature is several thousand degrees—it has occurred to me (and probably many others) that, throughout the universe, oceans of iron may be very common. Iron is, after all, the nineth most abundant chemical element in the universe. Iron oceans may prove to be as common as oceans of water.
Since iron is such an excellent solvent, especially for carbon and carbon compounds, it stands to reason that life-forms should be able to develop and evolve in oceans of iron just as easily as in oceans of water—if not more so. Thus it can also be said that life in this universe may be as common in iron oceans as in water oceans.
But if this is true, it begs a question that is both intriguing and (perhaps only to me) disturbing. You see, the earth doesn't actually have only one kind of ocean, it has two. On the surface it has an ocean of water, and deep inside it has a much larger ocean of iron—one ocean under an atmosphere, and one ocean under its crust.
Furthermore, all three of the requirements needed for life to arise and thrive exist in both.
Curiously, if there are single or multi-cellular animals swimming in earth's iron ocean hundreds of miles beneath our feet, regardless of their size or abundance or the vastness of their range, we would not be able to know it. Neither we nor our machines are capable of surviving the heat of the iron ocean long enough to search or explore, or even take a peek.
Only by examining the most iron rich volcanic rocks might we even hope to see their remains. And even that may not let us see them, because the depth where volcanic rock comes from may be far too close to the surface, and therefore far too cold a place, for them to visit.
So even if they exist in variety and vastness to rival the creatures of the rain forest we may never see them. And of course if we never see them, do they really exist?
And now I will tell you the real (and secret) title of this little essay. . .
Speculations on life in the ocean of iron beneath Earth's crust
Shhhh. Don't tell anyone.
Listen to Steve's podcast at http://www.thefutureandyou.com.
Stephen Euin Cobb is an author and the producer of the award-winning podcast The Future And You.