A celebrity scientist has sealed himself in an airtight foliage-filled chamber in a harrowing test designed to show the power of plants.
Professor Iain Stewart could stay up to two days inside the see-through container for an experiment linked to a new BBC2 series. The TV presenter and geologist is fronting the first programme in the channel's How Plants Made The World series.
He clambered into the transparent box, situated at the Eden Project in St Austell, Cornwall, on Thursday night.
The chamber measures 2m by 8m by 2.5 metres and is filled with 120 small plants and 30 large ones, all producing the vital oxygen he needs to keep him alive.
Prof Stewart, 46, from near Glasgow, moved to Plymouth to teach at the university in 2004. He said the project is designed to demonstrate the importance of plants to human survival as the "lungs of the planet".
Oxygen levels inside the chamber will be reduced from 21% - the normal atmospheric composition - to between 10% and 12%, which is equivalent to the amount of oxygen found at an altitude of 4,500m.
The professor of geosciences communication at Plymouth University, Devon, said: "Obviously when I'm in there I'll be using up oxygen, so the oxygen levels will be dropping and I'll be giving out carbon dioxide, so if it was sustained it would be a lethal combination.
"But six to seven hours in they're going to switch the lights on and the vault is packed with plants, which as soon as the lights come on, start to photosynthesise and should take the carbon dioxide that I'm breathing out, take that in, photosynthesises, and give back oxygen for me to breathe."
The maximum time the experiment could run is 48 hours. It may be forced to end early if either the carbon dioxide levels become too high or if there is a problem with Prof Stewart's response to the low levels of oxygen.
Specialist doctors from University College London's Centre for Altitude Space and Extreme Environment Medicine and the Royal Free Hospital will be monitoring him continuously and using him as a guinea pig for various tests to explore the effects of reduced oxygen.