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

Solidified magma from the Mid-Atlantic Divide.

The North American and European continental plates are being pushed apart. The magma thrusting up between the two cools and turns to new rock. As the continents move further apart, more and more rock is formed in convey-belt fashion, creating a historical record

Frozen within the rock are magnetic particles oriented towards the pole. They are observed to point different directions, depending on the age of the rock.

So, pole reversals.