"Tell me what happened!"

"The tree came apart.

"Why?"

"Maybe the fire set it off, but it was ready. Clave, everythiiing in the Smoke Ring has some way of getting around. Some way to stay near the median... middle, where there's warater and air. Where do you think jet pods come from?" The hanand relaxed a little, and the Grad kept talking. "It's a plant's way of gettmg around. If a plant wanders out of the median, t too far into the gas torus region--"

"The what?"

Alfin asked, "What on Earth is going on?"

'Clave wants to know what happened. Alfin, can you steer this thing and pick up some more of us? Here—" He passed across his store of jet pods.

Alfin took them. He took his time deciding what to do with them, and the Grad ignored him while he lectured. "The Smoke Ring runs down the median of a much bigger region. That's the gas torus, where the molecules... the bits of air have long meanfree-paths. The air is very thin in the gas torus, but there's some. It gets thicker along the median. That's where you find all the water and the soil and the plants. That's what the Smoke Ring IS living thing wants to stay."

"Where it can breathe. All right, go on."

"Everything in the Smoke Ring can maneuver somehow. An¬ imals mostly have wings. Plants, well, some plants grow jet pods. They spit seeds back toward the median where they can grow and breed, or they spit sterile seeds farther into the gas torus, and the reaction pushes the plant back toward the median. Then there are plants that send out a long root to grab anything that's passing. There are kites—"

"What about the jungles?"

"I... I don't know. The Scientist never—"

"Skip it. What about the trees?"

"Now, that's really interesting. The Scientist came up with this, but he couldn't prove it—"

The hand tightened. The Grad babbled, "If an integral tree falls too far out of the median, it starts to die. It dies in the center. The insects eat it out. They're symbiotes, not parasites. When the center rots, the tree comes apart. See, half of it falls further away, and half of it drops back toward the median. Half lives, half dies, and it's better than nothing."

In general I would be cautious against … plays of fancy and would not make way for their reception into scientific astronomy, which must have quite a different character. Laplace's cosmogenic hypotheses belong in that class. Indeed, I do not deny that I sometimes amuse myself in a similar manner, only I would never publish the stuff. My thoughts about the inhabitants of celestial bodies, for example, belong in that category. For my part, I am (contrary to the usual opinion) convinced ... that the larger the cosmic body, the smaller are the inhabitants and other products. For example, on the sun trees, which in the same ratio would be larger than ours, as the sun exceeds the earth in magnitude, would not be able to exist, for on account of the much greater weight on the surface of the sun, all branches would break themselves off, in so far as the materials are not of a sort entirely heterogeneous with those on earth.

It is at this point that the ultimate significance of dolphins in the search for extraterrestrial intelligence emerges. It is not a question of whether we are emotionally prepared in the long run to confront a message from the stars. It is whether we can develop a sense that beings with quite different evolutionary histories, beings who may look far different from us, even "monstrous," may, nevertheless, be worthy of friendship and reverence, brotherhood and trust. We have far to go; while there is every sign that the human community is moving in this direction, the question is, are we moving fast enough? The most likely contact with extraterrestrial intelligence is with a society far more advanced than we (Chapter 31). But we will not at any time in the foreseeable future be in the position of the American Indians or the Vietnamese – colonial barbarity practiced on us by a technologically more advanced civilization – because of the great spaces between the stars and what I believe is the neutrality or benignness of any civilization that has survived long enough for us to make contact with it. Nor will the situation be the other way around, terrestrial predation on extraterrestrial civilizations – they are too far away from us and we are relatively powerless. Contact with another intelligent species on a planet of some other star – a species biologically far more different from us than dolphins or whales – may help us to cast off our baggage of accumulated jingoisms, from nationalism to human chauvinism. Though the search for extraterrestrial intelligence may take a very long time, we could not do better than to start with a program of rehumanization by making friends with the whales and the dolphins.

The virtue of thinking about life elsewhere is that it forces us to stretch our imaginations. Can we think of alternative solutions to biological problems already solved in one particular way on Earth? For example, the wheel is a comparatively recent invention on the planet Earth. It seems to have been invented in the ancient Near East less than ten thousand years ago. In fact, the high civilizations of Meso- America, the Aztecs and the Mayas, never employed the wheel, except for children's toys. Biology – the evolutionary process – has never invented the wheel, in spite of the fact that its selective advantages are manifest. Why are there no wheeled spiders or goats or elephants rolling along the highways? The answer is clearly that, until recently, there were no highways. Wheels are of use only when there are surfaces to roll on. Since the planet Earth is a heterogeneous, bumpy place with few long, smooth areas, there was no advantage to evolving the wheel. We can very well imagine another planet with enormous long stretches of smooth lava fields in which wheeled organisms are abundant. The late Dutch artist M. C. Escher designed a salamander-like organism that would do very well in such an environment.

The fact that this chain of life existed [at volcanic vents on the seafloor] in the black cold of the deep sea and was utterly independent of sunlight—previously thought to be the font of all Earth's life—has startling ramifications. If life could flourish there, nurtured by a complex chemical process based on geothermal heat, then life could exist under similar conditions on planets far removed from the nurturing light of our parent star, the Sun.

Though one might imagine "living" organisms such as intelligent computers produced from other elements, such as silicon, it is doubtful that life could have spontaneously evolved in the absence of carbon. The reasons for that are technical but have to do with the unique manner in which carbon bonds with other elements. Carbon dioxide, for example, is gaseous at room temperature, and biologically very useful. Since silicon is the element directly below carbon on the periodic table, it has similar chemical properties. However, silicon dioxide, quartz, is far more useful in a rock collection than in an organism's lungs. Still, perhaps lifeforms could evolve that feast on silicon and rhythmically twirl their tails in pools of liquid ammonia. Even that type of exotic life could not evolve from just the primordial elements, for those elements can form only two stable compounds, lithium hydride, which is a colorless crystalline solid, and hydrogen gas, neither of them a compound likely to reproduce or even to fall in love. Also, the fact remains that we are a carbon life-form, and that raises the issue of how carbon, whose nucleus contains six protons, and the other heavy elements in our bodies were created.