Helium was a light element found on Earth (TV: The Robots of Death) with the symbol He on the periodic table. (TV: Shada) It was a gas at room temperature. (TV: The Robots of Death)
The Earth's Sun was made up of 74% hydrogen and 24% helium. (AUDIO: Feast of Fear)
Arcturus's life support system included a helium regenerator, which, if deactivated, he would die. (TV: The Curse of Peladon)
When humans inhaled large quantities of helium, their voices became high-pitched. The Fourth Doctor was able to use his respiratory bypass system to avoid its effects. (TV: The Robots of Death)
Helium 2 had the potential to exist during the Leptonic Era. (TV: Time and the Rani)
At CERN, liquid helium was used to cool superconducting electromagnets in a particle accelerator to -271.3°C. (TV: Extremis)