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Gold is just one of the many elements listed on the periodic table of elements. It's the one we humans have prized that most, the one we've used as money for millennia. And yet, why gold? Why not Why not osmium or lithium or ruthenium? Today, our Planet Money team tackles that question. Here are and David Kestenbaum and Jacob Goldstein.

JACOB GOLDSTEIN: For those of you who havent seen a periodic table since 10th grade chemistry, it looks kind of like a bingo card. Each square has a different element in it. There's a square for carbon, one for tin and another for gold.

DAVID KESTENBAUM: And were going to go through it kind of like a game of bingo. Crossing stuff out that wont work as money. Jacob. I am rooting for osmium.

GOLDSTEIN: I got a good feeling about lithium.

KESTENBAUM: To help us out. We have a professional - Sanat Kumar. Sanat knows all the elements in the universe, because he is chair of the chemical engineering department at Columbia University.

GOLDSTEIN: Sanat starts at the far right side of the periodic table. The things there have a really appealing characteristic. Theyre not going to change. Theyre chemically stable.

MR. SANAT KUMAR (Chairman, Chemical Engineering Department, Columbia University): Helium, Neon, Argon, Krypton, Xenon, Radon.

KESTENBAUM: Those are the Noble Gases.

MR. KUMAR: Correct.

GOLDSTEIN: So they're good in way because they're nonreactive. They're not going to change. Big drawback: a gas.

(Soundbite of laughter)

GOLDSTEIN: You could have your money like in jar. But then if you open the jar, youd be broke.

MR. KUMAR: Basically, yeah.

(Soundbite of laughter)

KESTENBAUM: If you're playing at home, you can cross out the right most column - Helium down through Radon.

GOLDSTEIN: So now, Sanat swings to the left most column of the Periodic Table, and he gets over to my pick, Lithium.

MR. KUMAR: If you expose lithium to air it will cause a huge fire that can burn through concrete walls.

GOLDSTEIN: Money that spontaneously bursts into flames: Bad idea. And it turns out that most of the elements out there are like Lithium, pretty reactive.

KESTENBAUM: Not all burst into flames. But youll get chemical reactions. You know how Iron rusts? Something similar might happen.

GOLDSTEIN: Based on that, Sanat crosses out another 38 elements. Then we ask him about these two weird rows at the bottom: The Lanthanides and Actinides.

MR. KUMAR: The Actinides are all radioactive.

KESTENBAUM: So these are, again, things that would not make a very good coin because you'd come back a year later and two percent of it would be gone, or something.

MR. KUMAR: Or maybe more than. But in the process you'd be dead, as well.

KESTENBAUM: Okay. Alright, you convinced us. We can cross those off.

(Soundbite of laughter)

GOLDSTEIN: So now we're down from 118 elements to 30.

KESTENBAUM: Our requirements so far: One, not a gas; Two, doesnt corrode or burst into flames; Three, doesnt kill you.

GOLDSTEIN: Now, Sanat adds a new requirement. You want the thing you pick to be rare. And this eliminates a lot.

MR. KUMAR: Titanium, Vanadium, Chromium, Manganese, Iron...

KESTENBAUM: But you dont want an element that is too rare. And that is why my favorite, Osmium, the densest of all the elements, gets the axe.

MR. KUMAR: Osmium is probably one of the rarest things around.

KESTENBAUM: Why?

MR. KUMAR: I have no clue. It apparently comes in with meteorites.

GOLDSTEIN: Now we're now down to just five.

KESTENBAUM: Ladies and gentleman, our final contestants are...

(Soundbite of drumming)

KESTENBAUM: Rhodium, Palladium, Silver, Platinum and Gold.

GOLDSTEIN: So, using just chemistry, weve ended up with only what are called Precious Metals.

KESTENBAUM: But even here we can cross things out. Silver has been used as money. But Sanat says it tarnishes, so it's not the best choice.

GOLDSTEIN: And early civilizations couldnt have used Rhodium or Palladium. Those werent discovered until the early 1800s.

KESTENBAUM: That leaves Platinum and Gold. You can find both of them in rivers and streams.

GOLDSTEIN: But if you were in the ancient world and you wanted to make Platinum coins, you'd need some kind of crazy furnace from the future.

KESTENBAUM: The melting point for Platinum is over 3,000 degrees Fahrenheit. Gold, just by chance, melts at a much lower temperature.

MR. KUMAR: It's things like that. I mean it's all these things that brought it together that makes Gold unique.

KESTENBAUM: So imagine were on Earth. We get to rewind the clock and lay out history again. Maybe it goes a different way. Do you think it would go a different way? Or do you think, you know, probably again humans would settle on Gold?

MR. KUMAR: Im convinced, given what we know now and reconstructing it, for the Earth with every parameter we have, Gold is the sweet spot. And it would come out no other way.

KESTENBAUM: Today, of course, we dont use Gold as money. We just use paper -which burns, can be found anywhere but it doesnt kill you.

GOLDSTEIN: In a future story, well talk about how we got to paper money.

Im Jacob Goldstein.

KESTENBAUM: Im David Kestenbaum, NPR News.

INSKEEP: You're listening to MORNING EDITION from NPR News.

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