For example, Stonehenge suddenly became older than the Pyramids, instead of younger.Since then, several other calibrations have been done, which confirm and extend the tree-ring one.However, the principle of carbon-14 dating applies to other isotopes as well.Potassium-40 is another radioactive element naturally found in your body and has a half-life of 1.3 billion years.We know (from other measurements) that the Sun hasn't fluctuated by more than 10 percent in the last million years.
This leaves out aquatic creatures, since their carbon might (for example) come from dissolved carbonate rock.
Some corals can be carbon dated, and also dated by another radioactive material, Thorium-230.
Pollen found in the Greenland icecap has been carbon dated, and also dated by counting ice layers. Trees grow a thick ring in a good year, and grow a thin ring in a bad year.
If you hear of a living tree being dated as a thousand years old, that is not necessarily an example of an incorrect dating. Wood taken from the innermost ring really is as old as the tree. We can date things for which historians know a "right answer".
And, we can date things that have been dated by some other method.
It is produced in the upper atmosphere by radiation from the sun.