Dating methods used in an archaeological excavation
In the ideal case, the geologist will discover a single rock unit with a unique collection of easily observed attributes called a marker horizon that can be found at widely spaced localities.
Any feature, including colour variations, textures, fossil content, mineralogy, or any unusual combinations of these can be used.
When rocks are subjected to high temperatures and pressures in mountain roots formed where continents collide, certain datable minerals grow and even regrow to record the timing of such geologic events.
To achieve this precision, geochronologists have had to develop the ability to isolate certain high-quality minerals that can be shown to have remained closed to migration of the radioactive parent atoms they contain and the daughter atoms formed by radioactive decay over billions of years of geologic time.
The stratigraphic column, a composite of these systems, was pieced together from exposures in different regions by application of the principles…
Local relationships on a single outcrop or archaeological site can often be interpreted to deduce the sequence in which the materials were assembled.
Continents move, carried on huge slabs, or plates, of dense rock about 100 km (62 miles) thick over a low-friction, partially melted zone (the asthenosphere) below.
In the oceans, new seafloor, created at the globe-circling oceanic ridges, moves away, cools, and sinks back into the mantle in what are known as subduction zones (i.e., long, narrow belts at which one plate descends beneath another).