Another technique used by archaeologists is to inspect the depth of penetration of water vapor into chipped obsidian (volcanic glass) artifacts.
The water vapor creates a "hydration rind" in the obsidian, and so this approach is known as "hydration dating" or "obsidian dating", and is useful for determining dates as far back as 200,000 years.
Circa Circa (from Latin, meaning 'around, about, roughly, approximately') – frequently abbreviated ca., or ca and less frequently c.,circ. – signifies "approximately" in several European languages and as a loanword in English, usually in reference to a date.
Circa is widely used in historical writing when the dates of events are not accurately known.
It also draws heavily from the field of ecophysiology, a branch of Biology, to ascribe spine or thorn characteristics to particular environmental or physiological variables.
The first peer-reviewed article to present and explain an isotope spine series was from a saguaro cactus in Tucson, Arizona.
Archaeomagnetic dating Archaeomagnetic dating is the study and interpretation of the signatures of the Earth's magnetic field at past times recorded in archaeological materials.
An annulus may also be an indication of growth in certain species, similar to dendrochronology.
For example, in fish, it is a series of concentric rings (or annuli) formed in the scales of bony fish.
The result is that along each external "rib" of the cactus is a series of spines arranged in the order they grew in – the oldest spines are at the bottom and the youngest spines are at the top.
These spines can be dated using bomb-spike Carbon-14 and isotopes of carbon (Carbon-13) and oxygen (Oxygen-18) may be used to infer past climate (e.g.
This technique is useful to about 9,000 years ago for samples from the western United States using overlapping tree-ring series from living and dead wood.