<p>The Earth's initial accretion was about 4.5 billion years ago, and there is good Hf-W isotopic evidence that an iron core started to form within about 10 M years, and may have been largely complete within 30 M years. However, the Earth's dynamo, which is driven by isotopic heating and core rotation/convection, didn't switch on strait away. It must have built up over hundreds of millions of years, possibly kick-started by a the magnetic field of a stronger solar wind at that time. The evidence from 3.5 Bn year old dacites suggest that the magnetic field at that time was only 30 to 50% of the current value. There is no magnetic data for 4.4 to 3.5 Bn years, (the time period you are interested in), but current models lean towards lower rather than higher values. There appears to be no mechanism for strong magnetism in the early Earth. Geomagnetic evidence from about 2.5 Bn years ago seems to indicate that the Earths magnetism was more stable then than now, with few if any peaks of high or low magnetism. Probably the Earth's early magnetic field will always be imprecisely known because nearly all the early rocks have been 'cooked' in such a way as to extinguish the early magnetic evidence.</p>

CC BY-SA 3.0
2015-11-30T12:48:18.183Z
This answer would benefit from some references or at least links.
Matt Hall
CC BY-SA 4.0
2018-07-14T14:52:56.763Z
Also it would help if you mentioned the magnetic field has flips
John
CC BY-SA 4.0
2020-06-24T14:17:49.850Z
the question asks over geological time and your answer is only about the creation of the magnetic field so a lot of information is missing and should be added or you can add links to some of the other Q&As about this.
trond hansen
CC BY-SA 3.0
2015-11-27T20:10:09.910Z
2015-11-27T20:10:09.910Z
Gordon Stanger
<p>Looking at the <a href="https://en.wikipedia.org/wiki/Earth%27s_magnetic_field" rel="nofollow">wikipedia article on the Earth's magnetic field</a>, I see that its strength varies through time. How did Earth's magnetic field change throughout its history, from the beginning of the Archean period (~4 billions years ago) to today?</p>

<p><strong>My current attempt</strong></p>

<p>All I found so far is <a href="https://upload.wikimedia.org/wikipedia/commons/9/9f/Brunhes_geomagnetism_western_US.png" rel="nofollow">this graph</a> from wikipedia (which is on a too short time scale) and <a href="http://www.rochester.edu/news/show.php?id=2842" rel="nofollow">this kind of text</a> (not a science paper) reporting an estimate for a given time point (3.2 billions years ago) reporting a field of about 25 microTeslas.</p>

<geophysics><earth-history><geomagnetism><paleomagnetism>
How did the intensity of Earth's magnetic field change through geological time?
Remi.b
# How did the intensity of Earth's magnetic field change through geological time?

(Asked by: username_0 on 2015-11-27)

Looking at the [wikipedia article on the Earth's magnetic field](https://en.wikipedia.org/wiki/Earth%27s_magnetic_field), I see that its strength varies through time. How did Earth's magnetic field change throughout its history, from the beginning of the Archean period (~4 billions years ago) to today?

**My current attempt**

All I found so far is [this graph](https://upload.wikimedia.org/wikipedia/commons/9/9f/Brunhes_geomagnetism_western_US.png) from wikipedia (which is on a too short time scale) and [this kind of text](http://www.rochester.edu/news/show.php?id=2842) (not a science paper) reporting an estimate for a given time point (3.2 billions years ago) reporting a field of about 25 microTeslas.

**Tags:** geophysics, earth-history, geomagnetism, paleomagnetism


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## 1 answers

### Answer by username_1 on 2015-11-27. Score: 3 | Accepted answer

The Earth's initial accretion was about 4.5 billion years ago, and there is good Hf-W isotopic evidence that an iron core started to form within about 10 M years, and may have been largely complete within 30 M years. However, the Earth's dynamo, which is driven by isotopic heating and core rotation/convection, didn't switch on strait away. It must have built up over hundreds of millions of years, possibly kick-started by a the magnetic field of a stronger solar wind at that time. The evidence from 3.5 Bn year old dacites suggest that the magnetic field at that time was only 30 to 50% of the current value. There is no magnetic data for 4.4 to 3.5 Bn years, (the time period you are interested in), but current models lean towards lower rather than higher values. There appears to be no mechanism for strong magnetism in the early Earth. Geomagnetic evidence from about 2.5 Bn years ago seems to indicate that the Earths magnetism was more stable then than now, with few if any peaks of high or low magnetism. Probably the Earth's early magnetic field will always be imprecisely known because nearly all the early rocks have been 'cooked' in such a way as to extinguish the early magnetic evidence.

> **Comments:**
> **username_2**: This answer would benefit from some references or at least links.  
> **username_3**: Also it would help if you mentioned the magnetic field has flips  
> **username_4**: the question asks over geological time and your answer is only about the creation of the magnetic field so a lot of information is missing and should be added or you can add links to some of the other Q&As about this.  

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