© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm

20.3.1  Telluric Civilizations

All human societies of which we are aware have been land-based. They also have all been found on Earth. How common are telluric civilizations throughout the rest of the Galaxy?

The first requirement is motivation. On this planet -- a typically exotic world -- examples abound. Ant lions and worm lions knock insect prey into their capture pits by hurling sand with the head. Termites build structures on the order of 100 "stories" high, and ants maintain flocks of dairy aphids which are milked regularly. Beavers build dams and dome-shaped lodges. Primates display a wide variety of tool-using behavior -- sticks are used for whips, clubs, spears, anthill fishing poles, toothbrushes, and as levers to pry open boxes, fruits, or nuts; leaves are used as drinking and feeding tools; and so forth.⁵⁶⁵ Tool-using behavior seems widespread among land-living species on Earth.

The second requirement (manipulators) is particularly easy, since ambulatory limbs which preadapt a species for tool-using are particularly suited to locomotion on land. Even the most primitive terrestrial vertebrate forms -- the amphibians -- have 5-fingered hands, two arms and two legs. Several species of lizards are known to have opposable thumbs, supposedly the hall mark of human tool manipulating ability. A few zoologists have speculated that if mankind were eradicated today it is likely that his technocultural replacement could evolve in as little as 15 million years.⁴⁰⁰ The raccoon would be one possibility, since its hands are thought by some to be superior to our own for grasping and manipulating. Pandas have evolved an alternative but satisfactory method of grasping using a thumblike appendage, and koala bears have not one but two opposable digits on their forepaws.450 Human related simian stock, such as chimpanzees and apes, might also replace us.

The third requirement is physical resources. As historian Richie Calder suggests, a technical culture can only manifest itself in the materials that are available from the physical environment:

The Eskimo, although an ingenious people and blessed with a remarkable memory, never developed beyond the Neolithic (New Stone Age) because of their very limited materials.. They had no access to ores that might have set them on the track of metallurgy; cold and snow prevented agriculture and made them hunters; they had no wood as they were beyond the tree line; and the lack of other plant life denied them fibers for weaving. Without these materials they simply were unable to evolve their own technology.⁹⁶⁸

Discussions among xenologists on the availability of technology materials frequently center upon the abundance of various metals on planetary surfaces. (See Bova,¹⁴⁰⁰ Huntington and Cushing,²⁶²⁰ and Livesay.²⁷²³) Astronomical aspects are best considered first. For instance, most Disk stars in the Galaxy should have sufficient metallicity to permit terrestrial planetary formation provided other conditions are also favorable. Core stars generally have even higher metallicity, so the physical resource factor is even more positive for the evolution of metal-using technical civilizations. Also, the older a star the sooner it was formed from the primordial galactic nebula -- and thus the fewer heavy elements it and its worlds may possess.²⁸⁷⁶

Planets located in mid-habitable zone (of the biocarbon ecosphere) normally will show heavy element compositions roughly similar to Earth, having condensed out of the primitive solar nebula at about the same temperature.²⁰⁵⁰ While the total fraction of heavy elements varies from star to star, the relative fraction of each metal is surprisingly uniform.¹⁹⁴⁵

While planetary bulk composition may stay relatively constant (in a given ecosphere around the star), there may be serious problems in surface distribution. As suggested in an earlier chapter, large worlds should have thinner crusts (which more easily buckle) and more severe tectonic activity. This activity will tend to thrust rich subcrustal heavy metal deposits to the surface, making them available for technological utilization. (Prospectors have long known that the richest mineral and ore deposits are generally found in regions of volcanic activity and in mountainous terrain.²⁹⁰⁹) Less-massive planets should have comparatively few concentrated ore deposits near the surface.

The fourth requirement for civilization is energy. Land dwellers are pretty well-off. Fibrous vegetation or animal oils can be burned, as can natural hydrocarbons tapped from pools or pockets of decaying organic matter. Fires permit smelters and the working of metal products, and the technology is on its way.*

* There may be a few unusual (to us) cases. For example, on a planet with a chlorine atmosphere heavy metals might serve as fuel. In Cl₂ gas, hot strips or wires of copper, or iron wool, spontaneously burst into flames.

Last updated on 6 December 2008