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

As the layers of rocks form the magnetic material aligned with the earth magnetic poles and roughly that time frame there is a slow progression of the magnetic material changing alignment to the movement of the earth’s magnetic poles.

Time frame was arrived at by how deep the layers are and looking at levels of elements left in the rock. Such as carbon 14 but I’m sure they looked at others as well.