Aliens everywhere? Pack your microscope...

kw: book reviews, nonfiction, science, astrobiology, space science

Peter Ward and his colleague Don Brownlee made a host of constituencies mad when they published Rare Earth four years ago. Their conclusion is that, while life in the form of microbes may be rather common throughout the Universe, complex animal life, however constituted, the kind of life that makes cities and spaceships and radio signals, is probably exceedingly rare. Read Rare Earth for a thorough, and thorougly entertaining, study of the requirements of complex life.

Agree or disagree, you'll find they raise questions that need to be discussed even as we imagine a universe like that of Star Wars or Star Trek. My own conclusion is that this portion of the Galaxy has only recently begun to produce civilizations: Stars formed (in this region of the Galaxy) prior to our Sun have too few heavier materials with which to form rocky planets such as Earth, large enough to hold an ocean for five or ten billion years.

Also, stars formed only 1-2 billion years ago have larger amounts of rocky material, but even a larger proportion of heavy metals and radioactive materials; they are likely to form super-earths that hold too much water (no continents), and stay hotter longer. So there is a window of opportunity, which may be rather narrow, maybe not. I think we are on its leading edge.

OK, with that out of the way, I say, "Who better than Peter Ward to discuss the various kinds of life that may arise, both here and elsewhere?" Complex life of any kind may be rare...or not. But life analogous to bacteria and viruses is likely to be found nearly everywhere. In his new book, Life As We Do Not Know It, Dr. Ward warns that it may be hard to recognize as life.

His opening example is telling. When subsea hydrothermal vents were first found, there was a lot of thin, snotlike material floating around. It got in the way of observations of the big clams, crabs, and tube worms. The scientists often had to move around or wait for the water to clear so they could get nice looking photos. It was quite a while before anybody thought to capture some of the slime and look at it. It turned out to be bacterial life, in a profusion that probably outweighs the nice clams and worms. It happens to be their food, too!

It seems ludicrous. Any grazing or browsing animal weighs less than the biomass of forage needed to sustain its life. So what did they think the clams and tube worms were eating? But this is just the problem. We don't really know the limits of earthly life, in terms of temperature, pressure, or chemistry.

If you take a pinch of soil from your yard, and spread bits of it onto petri dishes containing the ten or so common nutrient mixes you can get from places like Cuisenaire or Cole-Parmer or Ward, you'll get dozens or hundreds of bacterial colonies, and if you're lucky, perhaps twenty or thirty different species. If instead, you shake that same soil sample with water, then screen for the portion smaller than two microns. Pulverize and use genetic probes, you'll find evidence that there were tens of thousands (or even millions) of different species present.

Here, this'll blow your mind: Ordinary ocean water, whether sampled shallow or deep, contains three or four parts per billion of viruses. Doesn't sound like much...it comes to 20 to 50 million virus particles per cc! Not only that, but almost every living thing on the planet contains a ppb or so of viruses, including you our me. I we had a kind of light that "saw" only viruses, the entire biosphere and all bodies of water would be outlined in a ghostly filigree of viruses, down to its last detail.

To jump to the chase, the author presents his reasons for considering viruses as living beings. Though they require living cells to reproduce, there are many species of animal parasites whose biochemistry is defective such that they cannot live outside their host.

Just to make you feel secure: the vast majority of animal species are parasites. Even though some, such as the follicle mites that live in the forehead hair follicles of at least 95% of us, are called "commensal" because they don't seem to do harm (How they might benefit us is totally unknown. Any benefit is strictly one-way, so I call them parasites).

What is life? We need enough of a definition that we'll recognize it...we just can't fall back on "I'll know it when I see it." My own formulation: "Life is a process that results when aperiodic crystals grow in an environment strongly out of equilibrium". Dr. Ward proposes, "Life metabolizes, life replicates, life evolves." Simple and functional, and more testable. It doesn't depend on a particular kind of genetic mechanism or "bio"chemistry.

What kinds of non-Earth life might we find, somewhere (even on Earth)? The author proposes Terroan to designate "life as we know it", so we can then distinguish as alien, "life as we do not know it." Terroan life is composed of cells with a lipid cell membrane, is based on Carbon, Hydrogen, Oxygen, and Nitrogen (CHON), employs water as the main solvent, and uses DNA to encode and RNA to translate genetic codes to proteins via the Universal Genetic Code (UGC). In order of increasing "alienness", we might list

• Certain bacteria that slightly violate the UGC. For example, some mycoplasmas use one of the "stop" codes (the U-G-A sequence) to encode for tryptophan.
• The parent organism of our Mitochondria; these organelles have their own, somewhat different, genetic code and reproduce independently.
• Organisms using one of the approximately 10⁷⁵ other UGCs that might be devised, though only about 10⁵⁰ of them keep redundant codes in groups. The mycoplasmas mentioned above could be included here also.
• Viruses, which are non-cellular.
• Organisms that use a solvent other than water, such as methane or a strong ammonia/water solution at very low temperatures, or hydrogen sulfate (sulfuric acid if excess water is present) at high temperatures.
• Organisms that use a polymer other than DNA to encode its genetics. (Note that silicate rocks consist of Si-O and Si-Al-O polymers. Feldspar life?)

I can think of one attribute that might make really alien life hard to recognize. Velocity. Let's look at plants. How do you tell the difference between a living and freshly-dead slice of Oak leaf? Oak trees are proverbially slow growing, though they grow leaves quickly enough each Spring. Within the cells of the leaf, though, under the microscope you can see cytoplasmic streaming going on. The insides of a cell seem to revolve complete every two or three seconds, in spite of the fact that it is encased in a porous cellulose box. Loose cells from the inside of your cheek also show streaming as long as Oxygen is present, though it is slower.

Both animals and plants of Terroan life exhibit at some scale, motions that can be observed directly by our 20-frames-per-second visual systems. That is anything from a speed just faster than the minute hand on a wall clock to velocities that blur like a spinning figure skater. But suppose we find objects in an environment whose kinematics disallow motions of such rapidity, or that are composed of much stiffer material?

A science fiction story I read was about an odd rock in an astronaut's collection, kept in a terrarium with other rock specimens from the apparently desert planet he'd visited. Every week or so, it seemed this rock had moved a little. Finally, after setting up a time-lapse camera, he was able to see that, over a few months, the odd rock moved away from the more lighted part of the terrarium, then moved to the glass side and began slowly (very slowly) grinding at it, seemingly in an attempt to escape. Perhaps it "lived" on a time scale that to it, seemed like running to a barrier and grinding through in the space of a few moments. I wonder what the astronaut seemed like from its viewpoint?

We know, kinematically, living creatures that live ten or a hundred times faster are implausible. But there is no limit to how slow one may go.

There is a point to the book. We need to expand the "tree of life" to include viruses and RNA life, at the very least, so as to include all Earth-originated and/or -developed life. We think RNA life is extinct, if it originated at all. But it may be created soon in the laboratory. Bacteria with added DNA codes have been created in the laboratory, so they are aliens. Mars probably once hosted living creatures, at least bacteria or something similar; and it may do so today, some distance below ground. Europa might have life, though the energetics are forbidding. Titan seems to have a "just right" mix of energetics and complex chemistry, that life of some kind is likely.

Thus, Dr. Ward proposes that we send people to Mars and to Titan, to look for it. Because of the differing probable history, and the known differences today, a Paleontologist needs to go to Mars and a Biochemist to Titan (better, more than one of each!). Mars is likely to have fossils, and a Paleontologist by definition is good at finding fossils. Titan doesn't seem to have anywhere on its surface that could contain fossils, but is likely to have a strong chemical signature of life processes in many places. Just what a Biochemist is prepared to determine.

You know, that's a pair of really good ideas. I hope we do it. The biggest hurdle? We have to get used to the idea that a Saturn/Titan mission is definitely one-way. Radiation there is less than near Jupiter, but still deadly over the span of a few months at most (Jupiter orbit is a DOA environment at any arrival speed less than 0.1c). Mars is probably one-way also. Can we afford to send heavy digging equipment to Mars, so astronauts can get dug in before they die of radiation poisoning? Just getting there, the DNA in 1/3 of the body cells gets damaged per year of exposure to the interplanetary environment. You gotta get a hole dug first (10m deep at least), then go there fast. Then, there is a chance to return. Send a backhoe to Mars first!

Though I was a bit put off by Rare Earth, I understand the reasoning. I find Life As We Do Not Know It much more optimistic.