Io formed in Jupiter's orbit around the same time the Sol system was forming over four billion years ago. Due to its proximity to the massive gas giant, the moon has remained geologically active for billions of years.
Humans first set foot on Io during the Great Solar System Tour. Twenty years later, a massive lava tube was discovered and the first colony was established within the natural tubes in order to study the moon and Jupiter from a close distance.
As the moon was one of the most geologically active bodies in the system, massive drills excavated massive holes deep into the surface. These drills were then attached to massive space elevators which channeled the excess geothermal energy into orbiting magnets and soon starships leaving the system stopped by to tap the excess energy from the moon. This helped to curtail the overwhelming energy used by the moon
As the terraforming of the Sol System was underway, a few ideas were put forth on how to terraform the volcanic moon, but it wasn't until the year 12501 that the technology became available to safely create an atmosphere on such a world.
Taking hints from the terraforming of the Moon, initially Io was bombarded with many ice asteroids and comets, which had the desired effect of cooling the surface as well as creating a proto-atmosphere.
Due to the still geologically active nature of the moon, it was determined that the surface would most likely a desert world and as such terrestrial desert plants and animals were imported to seed the new world. Terraforming was completed in 13131 and the first surface settlements were built three years later.
The population is made up of humans who lived in dry desert climates.
Early Ioians were nomadic, moving across the warm desert volcanic landscape most of the time. Most of the small settlements exist around the small seas that dot the world. However current populations live in massive cities around the moon.
Due to its nature as a geologically active planetary body, the majority of oxygen producing life exists within the small lunar oceans. The plants and animals that live on the surface are all genetically engineered from terrestrial desert plant and animal stock.
Despite the terraforming effort there is still a large amount of volcanism, leading the night side of the planet dotted with lava. This, in addition to the many greenhouse gasses, keeps the moon warm.