| 1 | It has an atomic mass of two deuterium. | |
| 2 | The D/H ratio is the proportion of deuterium, or heavy hydrogen, in the water. | |
| 3 | Ocean water does have more deuterium than water in the Earth's mantle. | |
| 4 | Deuterium-based fusion reactors enter widespread use on Earth. | |
| 5 | It is a naturally occurring radioactive form of hydrogen, sometimes known as heavy hydrogen. |