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Thursday, May 9, 2013

Apocalypse – Loss of the Earth’s Magnetic Field (a guest post by Penny Higgins)

Some movies have put forward this idea that if we can disrupt the Earth’s magnetic field we’ll have an apocalypse. Think of that horrible movie “The Core.” This also comes up in the movie “2012.”
As it happens, there has been some discussion about whether or not disruptions of the Earth’s magnetic field could lead to extinction (or rapid evolution), because of the potential loss of shielding from cosmic radiation. There may be some truth to this, but it hasn’t been shown yet, at least not in any organisms with more than one cell.
Unfortunately (or maybe fortunately), disruptions to the Earth’s magnetic field tend to be so slow that they don’t really seem qualify as apocalyptic. A reversal (where the magnetic poles of the Earth switch places) is thought to take about 2000 years. Importantly, no-one says that the loss of the magnetic field will cause the Earth to fall apart! There are other planets in the solar system that lack magnetic fields (like Venus and Mars) and they’re doing just fine.
Let’s consider what would have to happen to shut down the Earth’s magnetic field (with some introduction to how the magnetic field works in the first place). Then, for giggles, let’s hypothesize what might actually happen should the Earth’s magnetic field suddenly cease to be.
Origin and Demise of the Earth’s Magnetic Field
I’ve already written a post about how the magnetic field of the Earth is formed. The key is that flow in the Earth’s liquid outer core causes the formation of the magnetic field. Some other planets (like Mars and Venus) lack a magnetic field because they lack either a liquid outer core (Mars) or flow in the liquid outer core (Venus).
The magnetic field of the Earth is known to have reversed multiple times during Earth’s history, with no discernible pattern or regularity. That is to say that while your compass needle points North now, at times in the past, it would point South. How this happens is not yet well understood. But what is known is that the Earth’s dipole magnetic field (the part that has north and south poles) decays away before it changes direction. (There is a non-dipole component to the Earth’s magnetic field, which honestly, I do not fully understand, so I won’t talk about it.) Sometimes reversals seem to be about to happen, and the field decays to nothing, then it recovers back to its original polarity. All told, the process seems to take a few thousand years to complete.
The Earth’s magnetic field protects the planet from the solar wind, a stream of highly energetic charged particles coming from the sun. It follows that when the magnetic field decays to zero, this cosmic radiation would strike the Earth and cause havoc. This is one of the premises of the movie “The Core.” (Also read more about The Core here.) If the magnetic field is lost, then the radiation should melt the Golden Gate Bridge, cause pacemakers to fail, and result in pigeons flying themselves into buildings.
Of course, none of these things could really happen, but it has been suggested that the increase in cosmic radiation during reversals could cause mutations in organisms increasing rates of evolution and potentially causing extinction or pseudoextinction (when organisms appear to have gone extinct because members of the lineage have evolved into a new, distinct morphology).
Evidence for Disruption
Is there any evidence that extinction or rapid evolution ever co-occurred with a reversal of the Earth’s magnetic field? I once asked this question and developed it into what became my senior thesis in the Biology Department at Fort Lewis College (all those years ago). My original plan was to lay out the geomagnetic polarity time scale and then plot alongside it the distributions of as many fossil species as I could find. It took me about a day to realize that the task was impossible. The biggest problem was that the resolution of the first and last appearances of the various species was not nearly precise enough to make a direct correlation. There are seldom numeric dates for the origination and extinction of species at all. The geomagnetic polarity time scale isn’t a whole lot better.
(Read about dating and the geomagnetic polarity time scale here.)
What I realized I needed was a situation where abundant fossils and the geomagnetic polarity could be collected and measured from the same rocks. I was disappointed when I realized that this meant abandoning looking at dinosaur extinctions and turning my attention instead to marine fossils, specifically microfossils.
The best study subjects were single-celled organisms that make tiny shells made of either calcium carbonate or silica. The shapes of the shells are what’s used to distinguish species. These organisms live in oceans and lakes, some as plankton floating with the currents, and others living on the ocean or lake floor. Because they’re small and common, it’s easy to look at evolutionary patterns or origination and extinction with them.
Radiolarians from Barbados
The rocks that the microfossils are found in, especially those of the ocean floor, are also great recorders of the state of the Earth’s magnetic field. Sea going vessels can drill into the ocean floor and pull up cores of the ocean floor sediments. The magnetic polarities can be measured directly from the core as it is passed through a magnetometer on the ships. These polarities can then be marked on the core, and corresponding samples of the cores can be taken. From these sample, microfossils can be isolated and identified, making it possible to directly correlation magnetic reversals with extinction events.
So? You ask. What are the results? What has happened?
James Hayes, in 1971, published a paper showing what he thought was evidence that extinctions in radiolarians (a type of single-celled organism that lives today but is also abundant in the fossil record) could be tied directly to reversals of the Earth’s magnetic field.  Ian Crain (1971) proposed that the loss of the Earth’s magnetic field could be lethal to some organisms, not because of an influx of cosmic radiation, but because the low field itself is disruptive to organisms.  Roy Plotnick, in 1980, published a paper showing that there is no demonstrable relationship between reversals and extinctions using the then currently available datasets. And since then, this topic hasn’t really been discussed, I suspect because the records are still insufficient to demonstrate a real relationship.
Magnetic Catastrophe
Let’s just say, for example, that the Earth’s magnetic field does suddenly shut down one day, just like what happens in “The Core.” Would it be an apocalypse? Would we be irradiated? Would microwaves melt our bridges?
Erm. No.
I imagine a lot of animals will get disoriented. Pigeons might fly in circles, unable to get home. Migrations might be disrupted. Salmon might have a hard time finding their home streams. Monarch butterflies might not make it back to their winter roosting trees in Mexico. So far, doesn’t seem to catastrophic. Some species might struggle and go extinct. The Sierra Club and Greenpeace and other such groups would probably go nuts. But it’s not terribly dangerous to humans, so far as I can tell.
Magnetic compasses would cease to work. That might have mattered more 50 years ago before GPS units and satellites. These days, our GPS’s can replace the old-fashioned compass.
Unless, of course, there’s some way that cosmic radiation can damage or disrupt the satellites that we’re dependent on. I wonder how long it would take the solar wind to shut down all the communication satellites we depend upon? That might be a problem.
But catastrophic?
Well, I guess it would kind of stink if suddenly airplanes didn’t know what way they were going. Oh yeah, but there’s those ground beacons, so I guess they’d be ok.
How about communications? Not everything is satellite-based. I’d be pretty cheesed off if I lost my 3G, but that’s dependent upon towers on the ground. I don’t call over seas very often, so the lack of satellite communication wouldn’t be the end of the world. Not for me anyway, and probably not for most people.
I guess, maybe, there’d be an increased chance of getting a sunburn what with all those extra cosmic rays? Invasion of the Lobster People, perhaps? I don’t think so.
So, really, what would happen if the Earth suddenly lost its magnetic field? Probably not much. Maybe a brighter aurora. Maybe some communications disruptions. Sure, some animals might be in trouble and go extinct. But nothing catastrophic.
It would just be inconvenient.
Penny Higgins
Vertebrate Paleontologist -- Isotope Geochemist

@paleololigo on Twitter


  1. Pilots navigated airplanes for decades without GPS. Between navigational beacons, gyrocompasses, and optical instruments they could do it again. But the margin of error with those techniques is much larger than with a good GPS, so air traffic controllers would have to enforce wider safety zones between aircraft in flight. That means fewer planes in the air, fewer available airline seats, and most likely higher prices for air travel. At least it would help alleviate high fuel costs.

    I know the electric utilities wouldn't mind too much if the Earth's magnetic field went flat. When the Sun blasts us with charged particles it warps the field like a hose spraying on a balloon. That warping induces currents in high tension power lines, causing safety breakers to trip and possibly shutting off power in large areas.

  2. My interest is astrobiology, and I find the terminology here a bit confusing.

    You can lump solar wind and CMEs with cosmic radiation, and I assume when you measure protons and nuclei there is an overlap.

    However due to the different energy regimes and sources the blocking mechanisms are different. Cosmic radiation is mostly blocked by the vast solar magnetic field (~ 90 %) and the rest by Earth's atmosphere. The Earth magnetic field doesn't help much there as I understand it, but it is true that part of the trapped particles in the van Allen belts are of cosmic origin.

    I think you skirted the possible confusion here though and it was my inexperience to see the 2-3 mechanisms (solar wind, CME and cosmic rays) mixed that was confusing at first.

    GPS satellites:

    They orbit at medium Earth orbit (MEO) at ~ 20 000 km altitude, in order to circle twice a day.

    This makes GPS satellites being positioned smack in the middle of the van Allen belts at 1000 - 60 000 km. MEO satellites thus experience all the drawbacks of intense trapped radiation combined with little if any protection from the field against outer sources.

    I assume the satellites are heavily radiation hardened, and loosing the Earth magnetic field would mean cheaper, less hardened satellites.

    Technically, bar low Earth orbit habitats (ISS, space tourism), the Earth magnetic field seems more of a nuisance than a resource. We could well be without for hundreds of millions of years before we loose too much water (cf Venus).

    Of course, I like me some plate tectonics for reasons of carbon cycling and what not. So I'm not proposing an anti-Core "Stop the mantle movement" movement, just to be clear. =D

  3. At closer consideration, maybe the trapped CR in the van Allen belts could be primarily of secondary origin, as the CR hits the atmosphere some secondary products would make it back. Meaning the CR blockage from the Earth magnetic field is minimal.

    Also, point of order: at least in my browser (Chrome) the link I provided don't show very well. Maybe the site could use another color/link scheme?