# Geodynamo
**URL:** https://boards.straightdope.com/t/geodynamo/75116
**Category:** Factual Questions
**Created:** [August 6, 2001, 2:13pm UTC](https://boards.straightdope.com/t/geodynamo/75116 "2001-08-06T14:13:10Z")
**Posts on this page:** 4
**Page:** 1
### Author:  [@QuickSilver](https://boards.straightdope.com/u/QuickSilver)
#### Post date: [August 6, 2001, 2:13pm UTC](https://boards.straightdope.com/t/geodynamo/75116/1 "2001-08-06T14:13:10Z")
Okay, so it appears that the magnetic field of the earth at the poles has reversed at least a few times during our planet’s history. Can anyone tell me what effect that had on the planet’s inhabitants (if indeed there were any the last time this happened)? Also, understanding that this kind of polarity reversal does not happen over night, what environmental effects can be predicted to occure when/as it does? Finally, is there anything that explains this phenomenon other than chaos? Oh, and really finally, if this were to happen again, would all bets be off on compass based navigation?
---
### Author:  [@Whack-a-Mole](https://boards.straightdope.com/u/Whack-a-Mole)
#### Post date: [August 6, 2001, 2:57pm UTC](https://boards.straightdope.com/t/geodynamo/75116/2 "2001-08-06T14:57:53Z")
[This](http://ees5-www.lanl.gov/IGPP/Geodynamo.html) site goes into some detail about this phenomenon.
> [@](#):
>
> Our solution shows how convection in the fluid outer core is continually trying to reverse the field but that the solid inner core inhibits magnetic reversals because the field in the inner core can only change on the much longer time scale of diffusion [2]. Only once in many attempts is a reversal successful, which is probably the reason why the times between reversals of the Earth’s field are long and randomly distributed.
It also states that the actual reversal takes about 1,000 years to complete.
I have found no mention of what effect such a reversal might have upon the biosphere. I imagine compass navigation would be right out the window. Do migrating animals sense the earths magnetic field? If so I imagine they’d be pretty screwed up as well. Beyond that I’m not sure such a thing would be noticeable at all to most animals or plants. (NOTE: That’s all a WAG on my part. I really don’t know and am just speculating).
---
### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [August 6, 2001, 3:41pm UTC](https://boards.straightdope.com/t/geodynamo/75116/3 "2001-08-06T15:41:28Z")
Certainly it has been asserted that some birds navigate with the aid of magnetic dorection, that is to say that tests were carried out that seemed to suggest that the birds sense of direction could be affected by artificial magnetic fields.
I’d imagine if it happens as frequently as 1000 year intervals, that any animals reliant on it have built-in coping mechanisms by now (or rather the ones that didn’t have to coping mechanisms simply aren’t here any more).
---
### Author:  [@Mangetout](https://boards.straightdope.com/u/Mangetout)
#### Post date: [August 6, 2001, 3:43pm UTC](https://boards.straightdope.com/t/geodynamo/75116/4 "2001-08-06T15:43:02Z")
oops misread, it’s not every 1000 years, it takes that long to shift, my bad.