Radioactive dating volcanic ash

17 Aug

Radioactive elements decay at a certain constant rate and this is the basis of radiometric dating.

But, the decay elements need to be set, much like you would re-set a stop watch for a runner, to ensure an accurate measurement.

However, sedimentary rocks can be age dated if a volcanic ash horizon or a diabase sill or dyke can be found within the sequence.

For example, if you find a dinosaur bone in a sedimentary sequence and you find an ash layer 10 meter above the bone and another ash layer 20 meters below it, you can determine the age of the two ash layers.

Each dark band represents a winter; by counting rings it is possible to find the age of the tree (Figure 11.22).

This pattern of growth results in alternating bands of light-colored, low density "early wood" and dark, high density "late wood".From the 1960s to the 1980s the oldest radiocarbon dates derived from analysis of settlement sites in New Zealand were 1000–1100 AD or even a little earlier.During the 1990s these dates were systematically re-assessed as the technique became better understood, and many problems were found with earlier dates.Droughts and other variations in the climate make the tree grow slower or faster than normal, which shows up in the widths of the tree rings.These tree ring variations will appear in all trees growing in a certain region, so scientists can match up the growth rings of living and dead trees.