Back dating tools
In the tropical rain forest, relatively few species of trees, such as teak, have visible annual rings.
The difference between wet and dry seasons for most trees is too subtle to make noticeable differences in the cell size and density between wet and dry seasonal growth.
Dating back to about 13,000 years ago, the "Clovis culture" was long thought to be the earliest human inhabitants of North America, but throughout the 21st century new finds consistently suggest the presence of an older culture.
These distinctive pointed tools were dated to be between 11,000 and 13,000 years old, and after others began turning up around the continent, the prevailing theory was that they belonged to the first settlers of the Americas.
These people were believed to have crossed over into Alaska from Siberia during the last ice age, when the Bering Strait had dried up, before spreading out across North and South America.
A small core of the wood is removed and the rings are painstakingly counted.
This remarkable tree was approximately 1400 years old, and grew on this rugged mountain ridge during the time of Mohammed.
There is clearly a difference between the calcium content of wood during the wet and dry seasons that compares favorably with carbon isotope measurements.