Prof Andrea Sella of University College London provides presenter Justin Rowlatt with a characteristically striking argument for why oxygen is so “incredibly dangerous”, and how its advent turned Planet Earth into a snowball.

Pawanexh Kohli, in charge of India’s national cold chain strategy, explains over a cup of chai why the oxygen needs of fresh vegetables and fresh meat are very different.

Physics polymath Baldev Raj unpicks the mystery of Delhi’s 1,600-year-old iron pillar, and explains just how damaging rust and corrosion can be.

And former “smoke-jumper” Frankie Romero explains the mesmerising attraction of wildfires, and why stamping them out isn’t always a good idea.

(Photo: Wildfire in Los Alerces National Park, Argentina; Credit: Emiliano La Salvia/AFP/Getty Images)