It's a bit tricky to definitively say which is the *oldest* living tree on Earth, as different methods of measuring age can give slightly different results. However, here are two contenders for the title:

* Methuselah: This bristlecone pine, located in the White Mountains of California, is estimated to be around 4,853 years old based on ring counting. It's considered the oldest known single-trunk tree in the world.

* Old Tjikko: This Norway spruce in Sweden is remarkable for its 9,550-year-old root system. While the current trunk is much younger, the tree has been able to regenerate itself from the same root system for millennia.

Therefore, while Methuselah is the oldest living tree in terms of a single trunk, Old Tjikko takes the title for the longest-living organism based on its continuous root system.