Archaeologists rely on a method called dendrochronology to identify the oldness of excavation sites.

The method, which involves studying tree rings, has proved to be a vital tool in the field of archaeology.  It can trace history up to 13,000 years back with the use of tree chronologies.

Trees grow differently, but all trees gain rings every growing season. The climate has a direct effect on tree growth. Trees will grow more rapidly and will leave wide yearly rings behind under the right climate, while harsh conditions like droughts and untimely cold will slow down growth and leave narrow rings.

Andrew Ellicott Douglass, an astronomer in the early 20th century, examined trees to find out how sunspots affect our planet’s climate. He discovered that trees located in the same area revealed the same pattern of rings, so he decided to record them as a way to note the area’s historical climate.

The astronomer went on to examine woods used in old pueblo sites and pieced them together to produce a regional chronology for use in dating archaeological sites.

Douglass’ research was partially subsidized by the National Geographic Society. It not only helped determine the actual age of the pueblo sites but also transformed the way archaeologists viewed excavation sites.

When archaeologists dig up timbre during excavations, they search for ring patterns that match in the regional chronologies to identify the site’s age.

Dendrochronology is a challenging  task in some areas such as in tropical settings where trees show similar seasonal patterns.

Nevertheless, the method has proven to be an essential tool that links disciplines such as climatology and art. It has also revealed records of drought in history, as well as the shift in indigenous forest regulation in the Central Amazon. It has also proven how archaeologists have found a great ally in trees.