EoArean Type

In the earliest ages of a solar system's history, long after the planets have been created but still eons before they have evolved into their mature forms, watery terrestrial worlds can be quite common.  Of course, various initial requirements must be met before liquid water can exist on any planetary surface, but if they are met then even worlds of relatively lesser mass can be host to the sparkling blue of seas and oceans.  For a time, anyway.

Nearly all young terrestrial worlds are geologically active, and it is this activity which is essential for the formation of a substantial atmosphere, and substantial stretches of surface water.  But worlds of lesser mass will lose their internal heat within one or two billion years, and although some measure of it will remain for billions of years more, there will not be enough to maintain an atmosphere or oceans.  Indeed, even early in its lifetime, a lesser mass world likely will not be hot enough to begin some form of geological cycle, such as plate tectonics.  Without this, there can be no long lasting biosphere.  Such worlds are doomed to retain almost no, if any, biosphere.  But for those early ages, even young Arean worlds can be oases of life.

Still warmed by a molten core, the surfaces of EoArean worlds are wracked with geological activity.  Great volcanoes may form, belching out gases and providing an atmosphere that might become quite thick.  Though much of this atmosphere is lost due to lesser gravity and harsh, young stellar winds, the prodigious volcanic activity maintains an equilibrium of sorts.  Surface water forms, and depending on conditions and elements present during the planet's initial formation, the amount may vary from small seas and scattered lakes to large, globe-girdling oceans.  As with nearly every place that water and energy are present, life will also invariably arise.  But the lifetime of these biospheres are limited, and for life to evolve into even microscopic but complex multicellular forms is exceedingly rare.  Nearly all such biospheres are inhabited by anaerobic microbes, single celled and quite primitive.

But in the end, these biospheres are consigned to a single fate.  As the planet's internal heat fades, so does its geologic activity.  Volcanoes begin to go extinct and the atmosphere slowly erodes away into space.  As the air pressure lessens over time, the planet will grow colder and the water will freeze, much of it retreating underground in great reserves of permafrost.  Life may often adapt if this change is slow enough, which it usually is, and by the time the world has become a seemingly barren Arean world, the only life remaining are those extremophiles which  manage to scrap out a living deep underground.

Oceans laden with sediment, these worlds are barren appearing from orbit.  But on the surface, simple life thrives in the dim oceans.


The dun-colored surface of an EoArean world;  yet there are ample signs of life along the shores.  Simple plant life and related forms may reach the stage of terrestrial colonization before the viability of the biosphere ends.

Quick Facts

Discovery:  EoAreans were long theorized as being a stage of planetary evolution for lesser massed worlds.  Evidence on Mars pointed to a wet past, and the eventual discovery of both fossilized and living anaerobic microbes on the Red Planet confirmed that, in the distant past, it had been a very different world.

Uses:  Despite their relatively short lifespan as a life-bearing world, EoArean planets are more than suitable as worlds for colonization, and indeed they are quite common planets.  However, depending on the age of the world, there is always the danger of excessive volcanism or meteoric impacts.


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ArcBuilder Universe concept John M. and Margo L. Dollan 2002-2004
This Page first uploaded May 1, 2004
Most recent update for this page June 16, 2004