Reverse magnetic dating
From the wealth of observatory and satellite data that document the magnetic field of recent times, we can model what the field would look like if we had a compass immediately above the Earth’s swirling liquid iron core.These analyses reveal an astounding feature: There’s a patch of reversed polarity beneath southern Africa at the core-mantle boundary where the liquid iron outer core meets the slightly stiffer part of the Earth’s interior.A polarity test typically determines the direction of current flow from a DC power source.(Battery, DC power brick, etc.) If the polarity the a power source is reversed, odds are the circuit will not function as designed.We’re turning to some perhaps unexpected data sources, including 700-year-old African archaeological records, to puzzle it out.
You might imagine the magnetic field is a timeless, constant aspect of life on Earth, and to some extent you would be right. Every so often – on the order of several hundred thousand years or so – the magnetic field has flipped. And when the field flips it also tends to become very weak.
What currently has geophysicists like us abuzz is the realization that the strength of Earth’s magnetic field has been decreasing for the last 160 years at an alarming rate.
This collapse is centered in a huge expanse of the Southern Hemisphere, extending from Zimbabwe to Chile, known as the South Atlantic Anomaly.
When the clay is heated to make a pot, its magnetic minerals lose any magnetism they may have held.
Upon cooling, the magnetic minerals record the direction and intensity of the magnetic field at that time.Direct current is simply a by-product of the generating process.