Reverse magnetic dating
Without a magnetic field, our atmosphere would slowly be stripped away by harmful radiation, and life would almost certainly not exist as it does today.
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.
Straight polarity means that the current is running from the electrode, to the metal, and back through the grounding clamp. Polarity in welding has to do with the direction of the current in the welding process.
With direct current (DC) the welding circuit can either be straight, or reverse polarity.
We’re turning to some perhaps unexpected data sources, including 700-year-old African archaeological records, to puzzle it out.
Earth’s magnetic field is created by convecting iron in our planet’s liquid outer core.
When the machine is set for straight polarity, the current…
It’s what makes compasses point north, and protects our atmosphere from continual bombardment from space by charged particles such as protons.
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.
If it is an electromagnet then just reversing the direction of current we can change the polarity.
You can't reverse a permanent-magnet's polarity, at least not without the equipment its manufacturer used.