| The major disadvantage of thoria are the environmental issues due to the exposure to the alpha particles emitted by thorium. |
| All natural rocks contain small amounts of uranium and thorium, which are radioactive and remain so for billions of years. |
| The dates of discovery of these elements as 1789 for uranium, 1829 for thorium, 1899 for actinium and 1913 for protactinium. |
| But a large region of rugged highlands on the far side, as well as heavily cratered patches on the near side, are poor in both iron and thorium. |
| Since gas mantles made with thorium are radioactive, their use has been phased out. |
| In addition to primeval heat, Earth's core also gets heat from radioactive decay of uranium, thorium, and potassium. |
