After the Cataclysm, much of the accrued knowledge of the world was lost. One of your priorities will be to find scholars who can recover this lost knowledge.
Elemental doesn’t have a traditional technology tree. Instead, it has 5 research categories (the Kingdoms and the Empires have different categories). When enough research has been done, a breakthru in that category is made and the player is presented with possible technologies to learn at that point.
When choosing a category, a given technology is color coded (green, yellow, red). Green means that technology will be available upon the breakthru being made. Yellow means it might be available. Red means it will possibly be available. In addition, there are certain technologies that are so rare that they are not displayed until the time of the breakthru.
Each new level of a given category takes more research to achieve than the previous. Hence, players have to be mindful of what technology they choose, particularly when deciding whether to pick up a rare technology that becomes available.
There are two primary ways of acquiring knowledge in Elemental. The first way is to construct improvements to your city that attract scholars. The second is to actually recruit famous scholars, inventors and other specialists as you find them.