eli5 – Why does Earth have a weak magnetic field and why is it weakening?
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Earth has a very active molten core which is what generates the magnetic field over time like the rest of the planets in our solar system it cools, when it does our planet may look like mars. Very weak magnetic field and constantly bombarded by solar radiation.
For Earth it’s thought to be due to the molten outer core which is liquid metal. The flow of this liquid metal generates an electric current and since the Earth rotates this generates an magnetic field (rotating electric fields create a magnetic field and vice versa).
As to why it’s weakening…….. that we don’t really understand. It’s thought that it’s possibly due to inner workings of the liquid outer core that we don’t really understand. However, after it weakens it’ll flip polarity and then strengthen again.
However, over time the outer core is solidifying and this will eventually most likely stop this but this will take a long time, like billions of years.
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From the geology 100 class I just took to my understanding. Earth magnetic field has a polarity normal and reverse. Now we know do to magnetism we find in millions of year old rocks that the Earth shifts polarity every now and again (it’s pretty inconsistent actually). Now we think we are in the middle of a polarity shift. Eventually the magnetism of the Earth will dissipate then shift polarity to reverse. Now we think this shift takes millions of years to accomplish so I wouldn’t really worry about it in any of our lifetimes but when we are in that moment that there is no magnetic field life will probably have a very hard time existing. So a polarity shift we think is happening rn so we’re coming from normal into reverse.
The current thinking is that it’s weakening because it’s in the process of reversing polarity. South will become north and vice versa. According to geological record, this occurs on a fairly regularly basis.
As for why the earth has a ‘weak’ magnetic field, I can only ask: compared to what?
Over the past 200 years the Earth’s magnetic field has weakened around 9%. There is specifically a “cold” spot called the South Atlantic Anomaly where a lot of that has happened. It’s not clear why or what it means. There’s no reason to think that it presages some catastrophe.
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