I have a situation where aliens need to pay Earth for something, they don't want to share their technology but they offer any naturally occurring chemical element.
Assuming that we'll get 10,000 tons, what kind of element makes the most sense to ask for? Precious metals, uranium or something else?
The payment is for the Earth as a whole and goes through UN, they will deliver to whatever address Ban Ki-moon decides.
I'm asking what is the most valuable element for Earth. Something that would be useful for us, but either we don't have it on the Earth or it's very hard to extract it.
I want to keep things simple so single chemical element in whichever allotrope or isotope we want, as long as it's occurring naturally in our galaxy. No exotic matter, anti matter, neutronium, transuranic elements ...