David Attenborough travels up in a high-altitude balloon. As the gases become thinner, the temperature becomes colder with an expanding rubber bladder showing how the air pressure drops as the balloon ascends. At 8,000 feet up David uses the equivalent of a vacuum cleaner to try catch small creatures that might be swept up into the atmosphere by convection currents. At 10,000 feet David has to wear all his warm clothing and use an oxygen mask to breathe as the pressure lowers and the air thins. At four miles up David empties out the apparatus but there are no large creatures to be found. Instead, he displays examples of creatures caught previously at this altitude. There are tiny spiders and winged aphids, all picked up by the wind. Despite freezing solid up here, they can be revived at lower altitudes, thawing out as they descend.