hi I'm Diana and you're watching physics girl so I grew up in Hawaii on the island of Kauai which is the oldest of 18 islands the wettest the greenest the most beautiful it had no nightlife there were 22 kids in my graduating class look hi nigra so the Hawaiian Islands are geologically weird they're formed by volcanoes we know that but we describe that they're formed by a volcano just one it's like an upside-down chocolate kiss conveyor belt there's a hotspot that form of the volcano and then the plates move over the top making the islands one by one OOP now you know so one of my childhood friends Noah Randolph flag became a geologist at UC Berkeley and when we were back home over the holidays we went for a hike and got talking about how unusual the formation of the Hawaiian Islands is it all started with a mystery world war two US military was looking for Japanese submarines in the Pacific and the way they did that is they lower a magnet off the side of the boat and the magnet would get pulled down if there was a metal submarine under there the military mostly used planes with these magnetic contraptions but scientists later adapted the technology for both and well presumably they saw some submarines I don't know about that but what they also saw was the magnet would go up and down so periodically on the ocean floor sometimes would pull really hard and sometimes it wouldn't pull very hard you have a thought online this was a mystery this magnetic contraption was made in wartime to search for submarines underwater but something else was pulling on it something unidentified and deep underwater I'm going to guess that it had to do with how much magma was close to the surface of the ground and because there's more iron I'm guessing in that rock then it pulled harder you're totally right it's about yeah it's it well you're probably Noah's brother Jeremy who's also a geologist just told me that I'm not totally right you're totally right then it's about the iron in the rock if you imagine a molten rock as being a bunch of little magnets floating around what direction do you think those magnets would would align I was glad that they would align along the magnetic field lines xre okay so we have all of these magnets in the molten rock that align with the Earth's magnetic field yeah and then they freeze and they're stuck there oh okay go on and the Earth's magnetic field would reverse and so what they were seeing was these stripes was the reversals of the Earth's magnetic field and what yeah what yeah and the other thing they noticed is across the Pacific it's symmetrical it looks almost like a barcode yeah and but it's a symmetrical barcode and they're like well that means that that all that crust has been produced in the same place and this is how we learned that the earth even has plate it's the number one thing you learn in earth science tectonic plates and we figured it out because these lines and little magnets aligned with Earth's magnetic field as it flipped over millions of years and that was frozen into the rock amazing the vast majority of volcanic activity on earth