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

There’s tiger stripes miles in width and thousands of miles long where freshly solidified unmagnetized rock is magnetized by the earths natural field. The rock is produced continuously, so when the field flips, the newer rocks are magnetized the opposite way from before, this making a boundary between one tiger stripe and the newest tiger stripe of magnetized rock