Knowledge

The 6th tab at the top.

It boosts elements production by investing them: putting some H will raise H production as a separate multiplier, for example.

The "default" Knowledge multiplier is 1.00, and each next invest raises it by 0.02 up to 2.00(+100%).

Getting 1.15(1.16 in fact, with 0.02 increments) multiplier unlocks next element in the group(or fist of next group) for investing.

Getting 1.80 multiplier buffs a separate "general knowledge" multiplier, which applies to all elements and starts at 1.00, by 0.01

Getting 2.00 multiplier(maxing element) reveals encyclopedic info about the element: name, symbol, atomic mass, etc.

Each next invest in a certain element costs ~1.15 times more(tested on As), meaning the total cost of maxing element is ~7220x cost of first invest.