• Question: Why do the Earth's magnetic poles reverse?

    Asked by dandav to Angus, Christian, Hannah, Laura, Simon on 18 Jun 2013.
    • Photo: Simon Holyoake

      Simon Holyoake answered on 18 Jun 2013:

      The magnetic field of the earth is thought to be produced by convection currents within the liquid and semi-liquid iron core, over time, the core changes orientation relative to the earth, and therefore the field slowly changes too

    • Photo: Hannah Bentham

      Hannah Bentham answered on 18 Jun 2013:

      This is a great question!

      But unfortunately we actually do not know for certain what causes the reversals. It is debated when the last reversal was (41,000 yrs ago versus 470,000 yrs ago). So it is difficult to know how they are caused if we do not have enough data to say when they have occurred.

      We do know that the earth’s magnetic field is generated in the outer Core. Also, we know the magnetic poles have wondered – the positions of the poles were different from the present day magnetic north and south pole. From creating geodynamo magnetic models, it seems like the Earth’s magnetic field decreases when the poles move far away from the geographical N-S poles and when the magnetic field decreases to ~10% then a reversal can happen.

      However, this is cutting edge research. Scientists still do not completely understand the processes that generate the magnetic field and there are a few scientists in my office who are working on such research. EXCITING STUFF!

    • Photo: Christian Maerz

      Christian Maerz answered on 19 Jun 2013:

      Can’t add anything to what Hannah wrote 🙂

    • Photo: Laura Roberts Artal

      Laura Roberts Artal answered on 19 Jun 2013:

      Hannah is absolutely right!

      We don’t know why the Earth’s magentic poles reverse and we don’t know when it might happen next. We also don’t understand what the effects of a reversal are, we can have a good guess at that though!

      We think that having a magnetic field is really important for life to be able to come about on a planet. What we don’t know is when the Earth first ‘got’ it’s magentic field. Was it at the same time as the planet formed (very unlikely) or later? Another really importat question is: when the magentic field formed, was it the same as it is today? We don’t think so, some people think it was much weaker, others think it was stronger. Was it able to reverse when it first formed? If so, that means that the Earth’s interior would have been quite similar to how it is today. It also means plate tectonics are likely to be working by then too.

      I’ve actually been looking for the oldest magnetic field reversal, but sadly I’ve not found it yet :(! That is science for you, it doesn’t always go the way you want. What I have found though is some of the best evidence to say that the Earth’s magentic field was active 3500000000 years ago!

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