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 in the earth were made and had metal in them. Metal being magnetic wanted to point the direction of the pole. So when they cooled it made lines of metal pointing to where the pole was. When we look at other rock samples the direction of the metal lines change. Newer rocks point opposite direction so we know they flipped