Primordial helium from the beginning of the solar system may be stuck inside Earth's solid core, new research suggests. The findings could have implications for a long-standing debate about how quickly our planet formed.
This rare form of helium is called helium-3 because it has two protons and one neutron in its nucleus. Normal helium, which is 700,000 times more common than helium-3, is called helium-4 because it has two protons and two neutrons. Whereas helium-4 is a common product of the decay of radioactive elements, helium-3 comes almost entirely from the initial cloud of dust and gas that formed the solar system.
