Now they have this sequence back several thousand years. To use this one must take a block of burned matrix out of the ground recording the exact location and direction. Then measure the angle of the ferrous ions. Its rough, but gives an independent date for a site or level. Each technique has its limitations, not only time range but also strength of date.
Calibration is still an important issue.
In the end, the trees are the surest dating method. We have come a long way from the Three Age system. Scarlett began this weeks discussion with the way of approaching the most common artifact, ceramics, with some of fundamental classifications of an artifact-form, function use, technology. Today we will continue on that theme with issues of classification and typology and types. The point is, we all classify and humans always have.