Forms the basis of archaeomagnetic dating
The earliest evidence of writing anywhere in the world only goes back about 5000 years.
Paleoanthropologists frequently need chronometric dating systems that can date things that are many thousands or even millions of years older.
But archaeology’s aim to understand mankind is a noble endeavor that goes beyond uncovering buried treasures, gathering information, and dating events.
A compass needle would have pointed to the south pole during some periods and to the north pole during others.
Lava and volcanic ash deposits often contain the thermoremnant magnetic records of these reversals.
The time between reversals has ranged between less than 100,000 to tens of millions of years with an average of about 300,000 years. It takes 1,000-8,000 years for one to be completed. It is thought that as a reversal approaches, the earth's magnetic field weakens.
It has been gradually weakening for the last 250 years.