• Question: Does the Earth's mantle have a magnetic field?

    Asked by wizzyg12 to Sam, Rob on 25 Jun 2013.
    • Photo: Sam Geen

      Sam Geen answered on 25 Jun 2013:

      Yep! It helps protect us from the charged particles bombarding us from the Sun. It’s made by the iron core of the Earth rotating.

      Edit – ah, wait, mantle? Unsure. I think it’s mainly the core that makes the magnetic field.

    • Photo: Robert Woolfson

      Robert Woolfson answered on 25 Jun 2013:

      Yes, an extremely weak one. The average fridge magnet is about 100 times stronger than the earths magnetic field, which is probably a good thing. If it was stronger, things like hard drives and all magnetic disk storage wouldn’t work as we wouldn’t be able to find the signals.

      Another interesting fact, we aren’t entirely sure how it’s generated. We think it’s due to the liquid iron that surrounds the core rotating. However, as we’ve never been to the core we have very little proof of this.

      The mantle doesn’t actually have a magnetic field itself, but it does keep a record of what our magnetic field has been during the life of the earth. As the magnetic field changes, metals in the rocks line up in different ways. This allows us to work out what direction the field pointed in and how strong it was, providing we know how old the rocks are.

Comments

  • Photo: Matt

    Matt commented on :

    Howdy! I’m going to weigh in a bit here as a geologist if that’s ok! The earths mantle is made up of mostly silicate rocks (mostly silica, or SiO2), with aluminium, magnesium and a bit of iron. Some of the iron forms minerals that are magnetic, but they do not generate a magnetic field. What makes the magnetic field is the rotation of the inner solid core made of iron, inside the liquid outer core, also made of iron. The movement drives what is called a “dynamo”. We have a pretty good idea about how this works because geophysicists have been exploring this with lots of different techniques for about 50 years. When mantle rocks melt and come out onto the surface to form the crust they cool and the iron lines up like a compass needle according to how the dynamo is lined up at that particular moment. So the whole Earth has a magnetic field (including the mantle) but it doesn’t come from the mantle! Hope this helps 🙂