Author: AndyB Page 1 of 2

Magnetic to the core was our stand at the famous Royal Society Summer Science Exhibition in central London.

There were loads of exciting activities, cool things to see and learn, and friendly researchers to talk to. Best of all, it was completely free!

Visitors discovered what happens to compasses as they pulled a lever to make Earth’s magnetic field reverse!

Others learnt about our fascinating field work and took a selfie drilling rocks like a real palaeomagnetist!

A really popular activity involved learning about how rocks contain magnetic minerals and using this to find out whether pebbles we gave out were safe to eat!

Visitors also measured the magnetic records within real rocks and found out whether they formed at a time when Earth’s magnetic poles were flipped.

More information about Earth’s magnetic field

• Take our quiz (you will be given a link to answers at end!)
• 10 things you might not know about the Earth’s magnetic field
• Videos introducing Earth’s magnetic field and palaeomagnetic fieldwork
• Twitter @LivUniGeomag #magnetictothecore #licensetodrill
• Instagram @magnetictothecore
• Our research pages

The Conversation has just published an article on its website about a recent paper published in Tectonophysics by Mark Hounslow, Mat Domeier and myself. I would be more comfortable with the title above but the one chosen was a compromise between this and the one they wanted which was MUCH worse. Anyway, happy with the article itself – you can read it here:

https://theconversation.com/the-earths-magnetic-field-reverses-more-often-now-we-know-why-96957

The Earth, apparently…

Determining Earth Evolution from palaeomagnetism (DEEP) is the new group formed within the University of Liverpool as a result of funding from The Leverhulme Trust. This exciting project will see us attempting to significantly improve global records of geomagnetic behaviour over the last billion years, capture that behaviour in statistical field models, and compare it with the outputs of numerical simulations of magnetic field generation in Earth’s core.

Palaeomagnetism (the study of records of ancient geomagnetic records preserved in rocks) has long been used to tell us about conditions in Earth’s core in the past but the idea with DEEP is to take this to a new level and try to answer some exciting outstanding  research questions which you can read on our official DEEP website.

Anyway, the big news is that, with the arrival of the first two PhD Students, Simon Lloyd and Daniele Thallner, we finally started last week! They join Courtney Sprain, our new post-doctoral research associate (PDRA) who started a week earlier on our NERC Standard Grant “Phanerozoic palaeomagnetic variations and their implications for the Earth’s deep interior”. They will also be joined by two more PhD students, three more  PDRA’s, and a NERC Independent Research Fellow over the coming months and years. Things are getting DEEP at Liverpool, and I for one, am pretty excited about that.

Delegates at the SEDI 2016 meeting – a prize to anyone who spots me…

All the standard text books say that Earth’s magnetic field is driven by convection. But what if it isn’t? I recently attended the SEDI (Studies of Earth’s Deep Interior) meeting in Nantes, France and was impressed by the work of Benjamin Favier and others looking into possible alternatives to the standard model of providing the power needed to drive the electric currents in Earth’s Outer Core that are responsible for our planetary magnetic field. These alternatives fall under the umbrella of “mechanical driving processes” and, as far as my limited understanding in this highly specialised field goes, the process can most easily thought of as “stirring” the fluid the outer core much as you would tea in a cup by doing work against resisting forces. However, clearly there is no tea-spoon involved. Rather, at the risk of pushing the analogy too far, the cup is being jiggled from the outside and it is the fluid’s interactions with the “container” (in this case the rest of Earth) as it sloshes about that is producing the flows.

So, what is doing the jiggling? We have already known the answer to this for a long time: interaction between the gravitational fields of Earth, the sun and the Moon cause variations in Earth’s shape and rotation. Because of the core’s elliptical shape, these variations are efficient means of converting gravitational energy into mechanical work (flows in the liquid).

The talk by Benjamin Favier (page 34 of this document) specifically focused on tidal forcing and on librations (small oscillations in Earth’s orbit). In it, he showed that these processes are very efficient at producing small scale flows within the outer core because of its very low viscosity and very high rotation rate. Together, he argued, they could easily account for the magnetic field we see today.  So, do they? After all, to paraphrase a comment made after the talk – “We KNOW the Earth is subject to such forcing, but we don’t KNOW  that the core is convecting”. Well, the jury is still a long way out. Benjamin confidently predicted the first fully self-consistent numerical mechanically forced dyanmos within a few years. The real challenge then will be to look at the magnetic behaviour they produce and compare it to that observed in the real Earth. The “Mechanical Forcing Brigade” (my name) face something of an uphill battle for the recent Earth because the convection-driven numerical dynamos are already doing a remarkably good job at replicating observed behaviour. My interest lies much further back in time. Before the inner core nucleated, it was much harder to generate buoyancy driven flow in the outer core; perhaps mechanical forcing had a (primary? Sole?) role to play in generating the magnetic field back then? Only comparisons between the next generation of dynamo simulations and newly updated palaeomagnetic records will tell us. I look forward to being part of that…

Pop-artist Andy Warhol famously stated that: “In the future, everyone will be world-famous for 15 minutes”. I suspect that yesterday may be the closest we will ever get to proving him right.

A paper on which I am lead-author claims that we have may have pinned down the point in Earth’s history when the inner core first started to freeze at the centre of the Earth to between 1 and 1.5 billion years ago.  I already thought this was big news so was a bit deflated when Nature decided not to run with the excellent picture (left) created by Kay Lancaster (cartographer at the University of Liverpool) on its cover.

Nevertheless, our excellent press officer at Liverpool helped produce a great press release which saw a story featured on the popular Phys.org website from the outset and an article in one of Spain’s top newspapers El Pais.

Things were a bit slow-burning for a while – except in India and Finland – before a  piece by Simon Redfern appeared on BBC news online. This was quickly followed up by a piece on the Daily Mail which our press officer tells me is the “most read online news site in the world”. A number of other things have followed including a post on one of my favourite blogs – IFLScience.

Then, just as I was packing up to go home, I received a phone call from the BBC World Service who wanted a short interview. I obliged in the evening and my nervous responses aired a few hours later. You can listen to the podcast here (it is the very last feature – “And finally…”). They refer before and after the interview to the finding as being that the magnetic field is much older than previously thought – incorrect in this specific case but relevant to another recent finding, albeit one that Liverpool people were not involved in making.

More informative is a piece I wrote for “The Conversation”.

A summary from our press office indicates that there are 39 news outlets and counting featuring the story  and tweets still coming through every few minutes. The coverage extends over at least 11 countries ranging from USA to China,  Argentina to Pakistan so, while I can, I am claiming (brief) world fame for our research…

Recently, I received an interesting email from Dmitry who wrote the following:

“According to the Dynamo theory Earth’s magnetic field is generated by rotating, convecting and electrically conducting fluid that maintain a magnetic field.

But what if it creates just by solar wind itself? In this case we don’t need to invent anything else to explain magnetic fields of planets. This process is similar to the principle of electromagnet.

Solar wind magnetizes planets. Now most of it just flies away of the Earth, but a small part of it passes mainly through the north and south poles.

This phenomenon may be also involved in heating the Earth’s core due to the conductor resistance, in the same way as wire is heated when electricity passed through it.”

Let me try to respond to this one piece at a time:

“According to the Dynamo theory Earth’s magnetic field is generated by rotating, convecting and electrically conducting fluid that maintain a magnetic field.”

Spot on – the fluid is in the Earth’s liquid outer core at a depth 2871 km and is convecting because of the release of light elements by the freezing of the inner core beneath it.

“But what if it is created just by the solar wind itself?”

This is already partly true. A small proportion (around 1%) of the Earth’s magnetic field (referred to as the external field) is produced by the interaction of the solar wind (charged particles from the sun) with similar particles within the Earth’s magnetosphere. This part is much weaker, more complex, and changes faster in time than the main part of the field.

“In this case we don’t need to invent anything else to explain magnetic fields of planets.”

Aah but we do. Venus is, in many ways, similar to the Earth and receives more solar wind (being closer to the source) and yet has a field that is 100,000 times weaker than Earth’s. The explanation? No core dynamo. And why not? Difficult to say for certain but likely because the core is not cooling fast enough to fuel a dynamo process.

“Solar wind magnetizes planets.” 

Yes it does but the effect is very small and relatively shallow. A subsurface exploration technique known as magnetotellurics measures the magnetic field induced in the ground by as a consequence of electric currents produced by the solar wind. The measured field variations are typically about 0.001 nT (nano-Tesla) over a period of hours and the resulting electrical currents go to a depth of a few tens of km. Compare this to the main internal field which has an intensity at the surface of around 40,000 nT and seems to come from the core with a depth of nearly 3,000 km. It is a small player.

“Now most of it just flies away of the Earth, but a small part of it passes mainly through the north and south poles.”

All true but the strongest external field variations are felt at the poles because that is where the existing internally-generated field is the steepest. Therefore, it is here that the solar wind particles can most easily travel down the field lines into the atmosphere.

“This phenomenon may be also involved in heating the Earth’s core due to the conductor resistance, in the same way as wire is heated when electricity passed through it.”

The principle here (Ohmic dissipation) is correct but, in practice, I would expect the core heating from this process to be vanishingly small. Pretty much all of the external field will be attenuated by the crust and converted (“dissipated”) to heat generated near the surface so none will be left to penetrate the core. Even close to the surface, the heating effect is very very minor compared to that coming from the Earth’s interior. A back of the envelope calculation gives, very approximately, a heating rate at a few tens of km down of about one-quadrillionth of a degree Celsius per second from these “telluric” currents. Compare this to natural geothermal gradients of tens of degrees per km and you get the picture that this is small-fry indeed.

I hope this post has answered your questions Dmitry and is useful to other readers. I would be very happy to respond to similar emails (or, even better, posts on this website) in the future.

Geochemistry, Geophysics, Geosystems (G3 or G-Cubed) is an online-only journal of the American Geophysical Union (AGU). It’s format means it is perfect for publishing papers with large supplementary information or appendices. That is definitely the case for this latest publication, lead-authored by Greig Paterson – a Scotsman in Beijing.

Measurements of the strength of the ancient magnetic field recorded in rocks  or archaeological materials (“palaeointensity” or “archaeointensity” measurements) can be very tricky to make. It would therefore be very useful to have some agreement amongst those people doing these experiments about what a reliable measurement looks like.  However, for one reason or another, such consensus has eluded the community for decades. This paper, we hope, is a step towards rectifying that. It uses the largest ever compilation of palaeointensity measurements made using only materials for which we know what the answer “is” (e.g. from lavas that cooled in recent times during which the magnetic field strength is independently known from observatory data). It then finds variants of currently used selection criteria that are better at picking out the reliable measurements than the originals. This stuff may not sound to the outsider as exciting as say, finding a new reversal, but it is the type of thing that underpins palaeomagnetism as a tool for understanding our planet better.

Certain mass extinction events, including the largest ever 250 million years ago, have been argued to have been triggered by the eruption of “large igneous provinces” (LIPs) – humongous plateaux comprising stacks of lava flows that erupted in relatively short amounts of time.

But how short a time? This is a crucial question as the atmosphere and oceans are pretty effective at processing the gases associated with volcanic eruptions in the short to medium term. So, unless the eruptions occur very close together (i.e. just years apart), there is not really much scope for them causing the kind of long term climate change that can wipe out large fractions of life.

Here at Liverpool, we just published a paper outlining a new tool for getting a handle on eruption rates based on the similarity of the magnetic field direction recorded in cooled lava flows that are on top of one another. The logic goes:

– the Earth’s magnetic field is changing direction all the time (which is why you have to change the declination on your compass every few years)

– when magma erupts and then cools, the magnetic minerals in the newly formed rock lock in a record of this direction

– if neighbouring lavas erupted within a few years of one another then the magnetic field direction will not have changed very much so the directions recorded in them will be quite similar.

This is not a new idea but the paper presents and tests a new parameter for formally quantifying the degree of this “next neighbour correlation”. The new parameter was shown to be an improvement over existing methods and its application to lavas from the  60 million year old “North Atlantic LIP” gave some quite surprising results. There was already independent evidence showing, that in one section of this large igneous province, there were pauses between eruptions that were, on average, several tens of thousands of years  long. Unexpectedly, significant similarity was observed in magnetic directions measured in neighbouring lavas from this section.

Records of palaeomagnetic strength fluctuations over millions of years have already hinted that the magnetic field displays some “correlation” over hundreds of thousands of years (that is, it may be consistently stronger or weaker on average during one period lasting a few hundreds of thousands of years that during another similarly long period). Our new study reports the first evidence that similar “correlation” may be present in the magnetic field direction as well.

Why is this important? Well, in addition to telling us more about the process that generates the Earth’s magnetic field, it also tells us we need to be careful in making the argument that similar palaeomagnetic directions in adjacent lava flows imply very fast eruption rates (as has been done previously). They may not and, with this requirement for rapid lava extrusion reduced, some of the lethality of the “killer LIPs” could be drawn into question too.