Nearby globular cluster NGC 6397 contains hundreds of thousands of ancient metal-poor stars (those that have few elements heavier than helium). Observations of a few hundred of these stars show that those burning hydrogen into helium all have about the same abundance of lithium.
ESO
Hydrogen and helium — the two lightest elements — make up some 98 percent of the universe’s mass. It may seem surprising, then, to learn that scientists figured out where the heavier elements came from before they understood the big two.
