In the American Southwest, the unbroken sequence extends back to 322 B. So, when an archaeologist finds a well-preserved piece of wood—say, a roof beam from an ancient pithouse—dendrochronologists prepare a cross section and then match the annual growth rings of the specimen to those in the already-established chronology to determine the year the tree was cut down. (Article available on the Indiana State University website.) The Laboratory of Tree-Ring Research in Tucson is the world's oldest dendrochronology lab; their website includes information for researchers and the general public.
The Science of Tree Rings is an educational website with lots of information—from basic definitions and principles to links to tree-ring databases and other resources.
For a long period in the 20th century Egyptian and Near Eastern chronology seemed to be the earliest of absolute chronologies, and imports from these areas were used to reconstruct the chronology of European prehistory.
With the introduction of objective quantifiable methods such as dendrochronology and Carbon-14 dating, over the past half century, European and North American archaeology have developed independent and more reliable chronologies, that often make it possible to date more precisely than in Egypt. For Egypt absolute year dates can only be established back to the beginning of the Late Period, from links to Greek chronology, and then from Assyrian king-lists and other Near Eastern sources, back to the Ramesside Period (still debated). The Egyptians dated by the year of reign of the king on the throne (for example 'year 3 of king X').
There was no definitive evidence as to what his eye or hair colour would have been so—given that this man was from Dublin—the decision was made to use blue eyes and medium brown hair, fairly typical of Irish complexion and colouring.
Using well-established marker points and specialised software the main facial muscles, soft tissue and skin were layered onto the digitised model of the skull.
Analysis of the skeletal remains had already established the age, gender, origin and likely social status of this individual and this information informed the final appearance of the reconstruction.
There was clear evidence for childhood malnutrition and heavy manual labour during life.
Four of the individuals (SK1 & SK3–5) were adolescents, so approximately 13–17 years of age at death.