Trees are vital for human life: they use up CO2 and pump out oxygen, as well as providing food, fuel and, err, climbing frames, too. But how big would a single tree need to be in order to sustain the human race?

A silly question, sure, but a fun one to answer—as this video from Earth Unplugged does. After working out how many trees there are on Earth right now—about 400 billion!—and how much oxygen they pump out, Maddie Moate manages to do some math to work how big that single, fictional life-giving tree would be. You're looking at something with a height of 130 meters and a trunk circumference of a whopping 122,064 meters. Watch the video to follow her reasoning. [Earth Unplugged]