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A varve is a sedimentary bed, or sequence of beds, deposited in a body of still water within a years time.
Counting and correlation of varves have been used to measure the age of Pleistocene glacial deposits.
Obsidian Hydration Dating This method is used to calculate ages in years by determining the thickness of rims (hydration rinds) produced by water vapor slowly diffusing into freshly chipped surfaces on artifacts made of obsidian or recent volcanic glass.
This method can be applied to glasses 200 to 200,000 years old.
Thermo Luminescence (TL) Dating This method is based on the phenomenon of natural ionizing radiation inducing free electrons in a mineral that can be trapped in defects of the minerals crystal lattice structure.
Although development of radiometric methods led to the first breakthroughs in establishing an absolute time scale, other absolute methods have limited applications.Chief among these are dendochronology, varve analysis, hydration dating, and TL dating.Dendochronology This method of dating is based on the number, width, and density of annual growth rings of long-lived trees.A master tree-ring index has been constructed in the southwestern United States for the Douglas fir and bristlecone pine.Dendochronologists can use this index to date accurately events and climatic conditions of the past 3000-4000 years.