Thermoluminescence dating of ocean sediments
The Earth's magnetic north pole can change in orientation (from north to south and south to north), and has many times over the millions of years that this planet has existed.The term that refers to changes in the Earth's magnetic field in the past is paleomagnetism.This process is called thermoremanent magnetization in the case of lava and clay, and depositional remanent magnetization in the case of lake and ocean sediments.In addition to changing in orientation, the magnetic north pole also wanders around the geographic north pole.The archaeologist then records the location of magnetic north on the cube, after the plaster hardens.
When the firepit cools the iron particles in the hardened clay keep this thermoremanent magnetization.
The Earth's molten core has electric currents flowing through it.
As the earth rotates, these electric currents produce a magnetic field that extends outward into space.
Any changes that occur in the magnetic field will occur all over the world; they can be used to correlate stratigraphic columns in different locations.
This correlation process is called magnetostratigraphy. Lava, clay, lake and ocean sediments all contain microscopic iron particles.