The ever effervescent Brian Cox is back on our screens here in the UK, following up his Wonders of the Solar System series with one looking at the Wonders of the Universe. The ‘Wonders’ phenomenon has even spawned its own drinking game!

Last night’s episode was called ‘Stardust – that’s why I love chemistry’, complete with a demonstration of what happens when you drop lumps of sodium into a plastic bottle half-filled with water. Those of you with access to the BBC iPlayer can see the episode here until mid April.

At one point, however, Brian trots out the usual line that there are 92 naturally occurring chemical elements on Earth. It was at this point that I decided to chastise him on Twitter and point out that I think it’s actually 94. What followed was a little bit of Twitter debate, calling into question whether 94 was any better of an answer than 92.

The reason I say 94 is that naturally occuring uranium can decay (all on its own, without any human intervention) to produce both neptunium and plutonium – albeit in trace amounts. So that’s 94. Of course, some of the other lower atomic weight elements are radioactive and don’t hang around forever (most notably technetium), but the fact is that they are found in nature.

So, if we define ‘naturally occurring’ along the lines of ‘elements that would be present on Earth without any influence from human activity’, I’m going to go with elements 1-94 fitting the bill.

Anyone disagree?

Stuart

Stuart Cantrill (Chief Editor, Nature Chemistry)