How do we know Earth’s magnetic fields flip in intervals of 200,000-300,000 years?

Question

Came across a (https://www.youtube.com/watch?v=g6thUIR3_rI) which describes Earth’s magnetic field having switched hundreds if not thousands of times during Earth’s 4.5 billion years.

So, how do we know thats a fact? What are scientists looking at that helped them determine this?

In: 2148

Answer 1

We don’t know it.

Some people make a projection based in the changes we can observe.

What phenomenon creates the Magnetic Fields? Why does the lava takes 300,000 years to change it if is in constant movement.