For millennia, gold has been used as currency. Our first records of the metal as money are from around 550BC, when King Croesus of Lydia began issuing his gold coins. So why was gold—not silver, platinum or any other element—first chosen as money, and why has it persisted for so long?

In this audio clip, chemical engineer Sanat Kumar examines all 118 elements of the periodic table to eliminate anything that couldn’t work as money, or wouldn’t work as well as gold.

When it comes to being currency, there’s some basic criteria. For example, you wouldn’t want your money to be radioactive. That crosses out 38 elements on the bottom of the periodic table. By contrast, 11 elements on the right side of the table are attractively chemically stable. But they’re also gases—so those wouldn’t work, either. Another 38 elements are eliminated because they may corrode or burst into flames. Twenty-five more are cut because they’re not rare enough to be a currency, or too rare. That leave us with just five contenders: rhodium, palladium, silver, platinum and gold. Listen above to the full exploration into why, when it comes to being money, nothing else quite matches the gold standard.