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

Rocks. There’s so to say tiny magnets in them. When this rock formed from cooled down lava, the tiny magnets aligned with the current magnetic field of the earth. By looking at the orientation of these tiny magnets and noticing a back and forth, it was deducted that the magnetic field flips. For determining the time frame, there’s statigraphy. Certain layers of rock are a certain age based on different properties like known fossilized species.