The Blue Age of Athas encompasses the earliest recorded history of the planet. Athas was a giant, world-spanning ocean broken only by a few small islands, and the sun was a pale blue. The only intelligent inhabitants were halflings and telepathic dolphins.
The halflings, who called themselves rhulisti, were masters of a now-forgotten science known as life-shaping, altering living organisms in to all manner of useful roles. However, something went wrong, and the Brown Tide - a contagion that spread through the oceans, killing life-shaped organisms - was created. The Pristine Tower was created to draw power from the sun to destroy the Brown Tide, but it also changed the sun to a bright golden colour and saw most of the planet's water drain away, revealing fertile plains and valleys. This was the beginning of the Green Age.