Like the rest of the Galilean moons, Europa formed around four billion years ago in Jupiter's orbital plane. The moon originally was a rocky body which was eventually covered in a thick ice sheet, the lower layer of which melted due to the influence not only of Jupiter's powerful magnetic field but also due to the hydrothermal vents located on the lunarwide ocean floor. Before terraforming, the ice sheet covering the ocean was around four to seven kilometers thick.
Much as how life formed in Earth's own oceans, the first semblance of life formed on Europa's ocean floor near the hytrothermal vents. Unlike with terrestrial life, however, Europan life began to evolve only around 3.9 billion years ago, millions of years after life began to evolve on Earth. Thanks to the protective layer of ice surrounding the inner oceans, mass extinction events were never experienced by the undersea life. Eventually, around the year 100000 BCE, the ancestors of the Kya appeared near a massive undersea volcano chain near Europa's equator.
First contact between the Kya and Humans came about when NASA’s Europa Clipper mission dug through the ice and discovered the first evidence of life. However, it was the ESA's Jupiter Icy Moons Explorer probe which took the very first image of a Kya hunting party sent to investigate the strange sounds emanating from the upper ice ceiling.
Missions to Europa began in earnest after this discovery. There were even proposals to terraform the moon. After a century of study it was concluded that melting the ice and giving the moon a thick warm atmosphere wouldn’t adversely affect the Europan lifeforms. In fact, many studies seemed to indicate that it would increase their living space. However, since the technology was not yet available, the only settlers allowed to live on Europa were placed in undersea habitats which were anchored to the ocean floor in order to tap the natural geothermal energy.
The first human to set foot on Europa did so in 2089, long before the Great Solar System Tour.
Europa's terraforming began in 4678 and began by the construction of large parabolic lenses in orbit to melt the surface ice. Gases from Jupiter were imported and used in the creation of the new atmosphere. In 5021 the terraforming of the moon was completed.
The human population of Europa is 1.5 trillion, most of which who live on floating cities above the water. The populaton of Kya is around 2.3 trillion.
The Europan culture is a fishing community mostly, as some Europan fish analogues are one of the most delicious meats in the Sol System.
The entire world is covered by ocean and since there is no land mass to block air currents, the winds continuously blow across the world rather predictably, and as such the storms of Europa are very predictable.
The temperature is constantly springlike.