BBC Business Daily’s Elements series is ending and we were very sad to hear that, but they just ran out of chemical elements to profile. The series followed elements across the periodic table and their roles from chemistry labs to the global economy. In the last-ever episode of the series, Justin Rowlatt look at the “obscure ones” — the rarest elements of the periodic table. He talks to minor metals merchant Anthony Lipmann, who explains how he made a fortune tracking down a stockpile of thallium, a toxic element sufficient to kill scores of people, and sold it to Japanese camera manufacturers. The series closes off with entering a different realm of scientific discovery entirely as cosmologist Martin Rees explains why 85% of the matter in the universe is not made up of chemical elements at all, but instead of dark matter (runtime 20:48).