The Big Guide to Humans: Home Planet

Humans come from a small, rocky planet, called Terra or Earth or some other translation of "dirt," where they lived on the land surface despite the planet being mostly covered (area and volume) by water. They do, however, measure temperature in a scale based approximately on the freezing and boiling points of water (at their average atmospheric pressure), set to 0 and 100. As with "years" (see lifespan and development), your local human can probably tell you the conversion to local measurements, if the knowledge is not in your local storage and the numbers are not being converted automatically by your translation dock. The planet's rotational axis is tilted relative to its orbital plane, resulting in "seasons," a predictable progression of local temperatures between local lows to local highs and back over the course of an orbit, despite its nearly round trajectory. This is in addition to the smaller temperature changes of the day/night cycle. Terran weather temperatures range from -90, below the freezing point of radon, to 60, nearly the boiling point of bromine, though humans mostly live where the weather over the course of a year ranges between -20 to 45.

Humans infamously breathe oxygen, but Terra's atmosphere is actually mostly nitrogen. The 23% oxygen concentration is enough for fires to sustain easily, assuming fuel and initial ignition, but low enough that fires smother nearly immediately when fully covered. Terra's rotation and heat from Sol combine to cause a predictable pattern of convection known as prevailing winds. Winds are often strong enough to move light objects without causing damage, not uncommonly strong enough to make it difficult for humans to move against it, or stronger, and sometimes strong enough to cause damage to buildings. This is in addition to regional threats of "extreme" winds, most notably tornadoes (fast-moving, localized funnels of winds strong enough rip buildings apart and fling heavy objects) and cyclones (weaker than a tornado, but traveling slowly and raining so copiously that shelters are also damaged by water).

Having such copious rain that buildings are damaged can happen outside of a cyclone, as well. While humans can swim surprisingly well for a non-liquid-dwelling species, this water has usually picked up so many contaminants that it is capable of overwhelming a human's immune system if it enters their body via their mouth or damaged skin.

Alternately, little or no water may fall on an area that does not usually experience water scarcity. The resulting "drought" kills plants and animals that cannot be moved. This is less predictable, but takes multiple years to come into effect. A vegetated area facing drought, however, is at particular risk for a wild fire, a fire that becomes too large and fast-moving to be smothered. Areas as big as residential ships can burned before the fire runs out of fuel or is able to be drenched.

Terra's planetary surface is made up of several pieces of "crust" floating on top of its liquid center. At the edges of these pieces, or at cracks in the pieces, huge pieces of crust can be forced upward or buckle under the pressure. Done slowly, so slowly no one notices, this produces mountains. Done quickly, it produces "earth quakes." Some earth quakes can only be sensed by sensors, but others cause buildings to shake apart. Humans know where these edges are and, instead of not building there, they design buildings that are able to resist being shaken. If the locus of the shaking is near or under the ocean, it can cause a fast-moving, towering wave called a "tsunami." An average tsunami is capable of obliterating buildings when it reaches shore, and then sucking any survivors into the ocean when it recedes (with strength far past even the best human swimmers). As with earth quakes, humans design buildings to survive being struck by this wall of water. The same edges and cracks also produce volcanoes, places where the earth's liquid center oozes or bursts out of the ground. This liquid will be at temperatures of 700 or more, above the melting temperature of radium and on past the the melting temperature of gold. It can cause fires when it touches things in addition to being so heavy and/or voluminous that it covers items in its path. Humans generally do not build very close to volcanoes that are frequently or explosively active. However, if a volcano is only likely to erupt once or twice within a human lifespan, or tends to ooze rather than burst, they will simply use several sensors to know when it will happen so they can get out of the way. Because they all originate in the same geological source, it is common to have two of these crack-based issues at once and not unusual to have all three.

Sometimes, rain falls in tiny frozen pieces, covering the ground in a layer of ice chips. Sometimes it falls in large rocks of ice, breaking and shattering what it strikes. Sometimes the temperature is anomalously hot or cold in places where the wildlife and human dwellings are not adapted to those temperatures. Sometimes massive sparks of electricity shoot from the sky to the ground. Sometimes the side of a mountain — or the ice chips piled on the side of the mountain — will fall off and slide down, burying and crushing everything in the way. Sometimes erosion under the surface will cause the surface to give way, leaving a hole in the ground big enough to swallow a person or a building. Sometimes the liquid inside Terra doesn't burst through the surface, but super-heats water until it does. While none of these features are unique to Terra, even among inhabited planets, it is uncommon for an inhabited planet to have so many of these features and it is nearly unique among humans to choose to live in afflicted areas. It can be helpful to understand, when one is wondering why humans and other life from their planet are "like that," that life only evolved on Terra once* and then experienced a burst of population up to and beyond local carrying capacities. Every species, including the plants, shares a common ancestor, and every creature that was ever born (hatched, sprouted, divided, etc) faced immediate competition from other, similar creatures. The ability to run faster, eat weirder, live hardier, spread farther provided an immediate benefit. Furthermore, in addition to the horrors described in this chapter of this guide, in Terra's planetary history there are multiple near-extinction-level events — new chemosynthetic species producing upheavals in the atmospheric gas balance, an asteroid strike, massive volcanic eruptions choking the air with ash and blocking energy from Sol — that further pressed evolution. Terra, truly, has earned its reputation as a death world — but less so for the life that has formed there.

*there is a long-standing idea that cephalopods may have originated separately, but this is really only taken seriously by the Chiparsen, who used to colonize via panspermia. While the Unified Government no longer accepts this as a valid territorial claim, the Chiparsen still hope to prove relation in order to put forth a diplomatic demand that Terrans remove cephalopods from their diet.