The sublime, almost fearful nature of deep time sometimes awes me even more than the kind of distances we routinely discuss in these pages. Yes, the prospect of a 13.8 billion year old cosmos strung with stars and galaxies astonishes. But so too do the constant reminders of our place in the vast chronology of our planet. Simple rocks can bring me up short, as when I consider just how they were made, how long the process took, and what they imply about life.
Consider the shifts that have occurred in continents, which we can deduce from careful study at sites with varying histories. Move into northern Quebec, for example, and you can uncover rock that was found on the continent we now call Laurentia, considered a relatively stable region of the continental crust (the term for such a region is craton). Move to the Ukraine and you can investigate the geology of the continent called Baltica. Gondwana can be studied in Brazil, an obvious reminder of how much the surface has changed.
Image: With Earth’s surface constantly changing over time, we can only do snapshots to suggest some of these changes. Here is a view of the Pannotia supercontinent, showing components as they existed about 545 million years ago. Based on: Dalziel, I. W. (1997). “Neoproterozoic-Paleozoic geography and tectonics: Review, hypothesis, environmental speculation”. Geological Society of America Bulletin 109 (1): 16–42. DOI:<0016:ONPGAT>2.3.CO;2 10.1130/0016-7606(1997)109<0016:ONPGAT>2.3.CO;2. Fig. 12, p. 31. Credit: Wikimedia Commons.
Studying these matters has something of the effect of an earthquake on me. By which I mean that in the two minor earthquakes I have experienced, the sense of something taken for granted – the deep stability of the ground under my feet – suddenly became questionable. Anyone who has gone through such events knows that the initial human response is often mystification. What’s going on? And then suddenly the big picture emerges even as the quake passes.
So it can be with scientific realizations. Let’s talk about how scientists use various methods to study rock from different eras to infer changes to Earth’s magnetic field. Tiny crystal grains a mere 50 to a few hundreds of nanometers in size can hold a single magnetic domain, meaning a place where the magnetization exists in a uniform direction. Think of this as a locking in of magnetic field conditions that can be studied at various times in the planet’s history to see what the Earth’s magnetic field was doing then.
The subject is vast, and the work richly rewarding for anyone asking questions about how the planet has evolved. But now we’re learning that it also holds implications for the evolution of life. In a new feature in Physics Today, John Tarduno (University of Rochester) explains his team’s recent work on paleomagnetism, which is the study of the magnetic field throughout Earth’s history as captured in rock and sediment. For the magnetic poles move, and sometimes reverse, and within that history quite a story is emerging.
Image: The University of Rochester’s Tarduno, whose recent work explores the effects of a changing magnetic field on biological evolution. Credit: University of Rochester.
For Tarduno, the implications of some of these changes are striking. They grow out of the fact that the magnetic field, which is produced in our planet’s outer core (mostly liquid iron) continually varies, and the timescales involved can be short (mere years) or extensive (hundreds of millions of years). It’s been understood for a long time that the field reverses its polarity, but accompanying this change is the less known fact that a polarity change also decreases the field strength. Sometimes these transitions are short, but sometimes lengthy indeed.
Consider that new evidence, presented by Tarduno is this deeply researched backgrounder, shows that some 575 to 565 million years ago the Earth’s magnetic field all but collapsed, and remained collapsed for a period of tens of millions of years. If that time range piques your interest, it’s probably because this is coincident with a period known as the Avalon explosion, when macroscopic animal life, rich in complexity, begins to appear. And now we’re in the realm of evolution being spurred by magnetic field changes. The implications run to life’s own history and even as far out as SETI.
Named after the peninsula in which evidence for it was found, the Avalon explosion occurred tens of millions of years earlier than the Cambrian period which has heretofore been considered the time when complex lifeforms began to appear on Earth. It came during the Ediacaran period that preceded the Cambrian, and seems to have produced the first complex multicellular organisms. The sudden diversification of body scheme and distinct morphologies has been traced at sites in Canada as well as the UK.
Image: Archaeaspinus, a representative of phylum Proarticulata which also includes Dickinsonia, Karakhtia and numerous other organisms. They are members of the Ediacaran biota. Credit: Masahiro miyasaka / Wikimedia Commons.
So this is an ‘unexpected twist,’ as Tarduno puts it, that may relate significant evolutionary changes to the magnetic field as it reconfigured itself. Scientists studying the Ediacaran period (between 635 and 541 million years ago) have found that rocks formed then show odd magnetic directions. Some researchers concluded that the magnetic field in this period was reversing polarity, and we already knew that during a polarity reversal (the last was 800,000 years ago), the magnetic field could take on unusual shapes. Recent work shows that its strength in this period was a mere tenth of the values of today’s field.
This work was done in northern Quebec (ancient Laurentia), but later work from the Ukraine (Baltica) and Brazil showed an even lower field strength. We’re talking about a long period here of ultralow magnetic activity, perhaps 26 million years or more. Events deep inside the Earth’s inner core seem to have spurred this. I won’t go into the details about all the research on the core – it’s fascinating but would take us deeply into the weeds. For now, just consider that a consensus has been building that relates core activity to the odd Ediacaran geomagnetic field, one that correlates with a profound evolutionary event.
Image: This is Figure 2 from the paper. Caption: Changes deep inside Earth have affected the behavior of the geodynamo over time. In the fluid outer core, shown at right, convection currents (orange and yellow arrows and ribbons) form into rolls because of the Coriolis effect from the planet’s rotation and generate Earth’s magnetic field (black arrows). Structures in the mantle—for example, slabs of subducted oceanic crust, mantle plumes, and regions that are anomalously hot or dense—can affect the heat flow at the core–mantle boundary and, in turn, influence the efficiency of the geodynamo. As iron freezes onto the growing solid inner core, both latent heat of crystallization and composition buoyancy from release of light elements provide power to the geodynamo. (Left: Earth layers image adapted from Rory Cottrell, Earth surface image adapted from EUMETSAT/ESA; right: image adapted from Andrew Z. Colvin/CC BY-SA 4.0.)
In the models Tarduno describes, the Cambrian explosion itself was driven by a greater incidence of energetic solar particles during periods of weak magnetic field strength. Thus we have the basis for a weak field increasing mutation rates and stimulating evolutionary processes. Tarduno cites his own work here:
Eric Blackman, David Sibeck, and I have considered whether the linkage might be found in changes to the paleomagnetosphere. Records of the strength of the time-averaged field can be derived from paleomagnetism, whereas solar-wind pressure can be estimated using data from solar analogues of different ages. My research group and collaborators have traced the history of solar–terrestrial interactions in the past by calculating the magnetopause standoff distance, where the solar-wind pressure is balanced by the magnetic field pressure… We know that the ultralow geomagnetic fields 590 million years ago would have been associated with extraordinarily small standoff distances, some 4.2 Earth radii (today it is 10–11 Earth radii) and perhaps as low as 1.6 Earth radii during coronal mass ejection events.
As Tarduno explains, all this leads to increased oxygenation during a period of magnetic field strength diminished to an all-time low, along with an accompanying boom in the complexity of animal life from the Ediacaran leading into the Cambrian.
Notice the profound shift we are talking about here. Classically, scientists have assumed that it was the shielding effects of the magnetic field that offered life the chance to survive. Indeed, we talk about a lack of magnetic fields in exoplanets like Proxima Centauri b as being a strong danger to life because of incoming radiation. This new work is saying something profound:
If our hypothesis is correct, we will have flipped the classic idea that magnetic shielding of atmospheric loss was most important for life, at least during the Ediacaran Period: The prolonged interlude when the field almost vanished was a critical spark that accelerated evolution.
Maybe we have been too simplistic in our views of how a magnetic field influences the development and growth of lifeforms. In recent decades, work has been showing linkages between these magnetic changes, which can last for millions of years, and spurts in evolutionary activity. So that it is precisely because of low magnetic field strength, rather than in spite of it, that life suddenly explodes into new forms during these periods of high activity.
Jim Benford has often commented to me that despite having mounted the most intensive SETI search with the most powerful tools ever available, we still have not a trace of a signal from another civilization. Is it possible – and Jim was the one who pointed out this paper to me – that the reason is that the magnetic field changes that so affected life on our planet are rare elsewhere? Because it now looks as though a magnetic field should be considered less a binary situation than as a variable, one whose mutability because of core activity can take the world it engulfs into periods of low to high magnetic strength, and some eras millions of years long in which there is hardly any field at all.
I mentioned Proxima Centauri b above. Whether or not it has a magnetic field has yet to be determined, which points out how little we know about such fields around exoplanets at large. Further investigation of Earth’s magnetic past will help us understand how such fields change over time, and whether Earth’s own history has been unusually kind to evolution.
The article is Tarduno, “Earth’s magnetic dipole collapses, and life explodes,” Physics Today 78 (4) (2025), 26-33 (abstract).
There were other environmental effects at that time, including the increasing oxygenation of the oceans and atmosphere. As regards the magnetic field strength, we know that about 5 meters of water is sufficient to block the solar wind and even cosmic rays. This means that the marine life would only have been affected in very shallow water. Any deeper and the sea water itself would have shielded the life. The few Ediacaran specimens we know of are those living on the sea bottom, although we have very little idea of what they looked like or how they lived.
If magnetic variation was so important, wouldn’t we expect that reversals with periods of low strength have shown effects at other times too? In addition, the field at the magnetic poles increases the charged solar wind density. We see that as auroras. Wouldn’t this, therefore, increase the rate of evolution at the poles?
We know that radiation, especially neutrons, can damage DNA, but can also, rarely, create beneficial changes. [I’m old enough to recall that exposing seeds to nuclear radiation could change the traits of wheat. Ah, the “heady” days before we could manipulate DNA and genes.] But we also know that some organisms, notably Deinococcus radiodurans, are extremely radiation resistant. Why did this trait evolve? It would certainly counter DNA modification with increased particle density during low magnetic field strengths.
Bottom line is that I am skeptical that a grand theory to explain a burst in evolution occurred that was coincident with one example of low magnetic field strength. The events may be purely coincidental, rather than causal. Because we know so little about the organisms at that time, with no living clade members (AFAIK), the best we can do is look at the genomes of existing species ti see if there is anything indicative that something genetically important can be inferred as happening at that time.
“We know that radiation, especially neutrons, can damage DNA, but can also, rarely, create beneficial changes.”
I can see how this could be true. On a population scale, the increased death toll may be survivable during periods where the radiation also increases the rate of beneficial or neutral mutations. However, the knee in curve would soon be encountered and the population would suffer, perhaps to the point of extinction or to favor sub-populations that selectively inhabit deeper waters (5 meters, was it?).
On the broader scale of time, this smells more like a coincidence rather than a positive correlation.
Editing note: In one instance Tarduno is misspelled Carduno.
Thanks, Ron. Will fix right away.
The article link is paywalled, but these are useful: https://www.smithsonianmag.com/smart-news/earths-magnetic-field-nearly-collapsed-600-million-years-ago-then-weird-and-complex-life-evolved-180984353/ https://www.nature.com/articles/s43247-024-01360-4
The argument might be that the weak magnetic field caused hydrogen to be lost from the atmosphere, driving an increase in molecular oxygen concentration. There’s a graph in the Nature article. But the relation of this to the Baykonurian “snowball Earth” glaciation and the nutrients available to cyanobacteria… it seems like there is a lot of room for specuation.
Incidentally, Tarduno was on a different paper doing simulations suggesting that day-length variations imply an “inverse topography” of kilometers-high mountains of the mantle rising down into the Earth’s liquid outer core. https://arxiv.org/abs/2410.19934 It is interesting to consider that there is a map of the entire Earth which is just beginning to be sketched ( https://academic.oup.com/gji/article/198/1/55/604258?login=false ). It does invite vain daydreaming about what sort of silicon and metal forests and scenic hamlets might nestle among those hills.
Quote by Alex Tolley: “If magnetic variation was so important, wouldn’t we expect that reversals with periods of low strength have shown effects at other times too? Exactly. Also DNA adapts to the environment through Darwinism. The DNA already gets enough radiation for mutation. Consequently, it has to be environmental change. The snowball Earth period was from710- to 640 Million years ago. Supercontinents are associated with warmer periods due to less coastline and less basalt weathering. Wikipedia. Furthermore, Less land mass in the northern hemisphere and more towards the equator would cause more sunlight to be on land and therefore a warmer climate. The climate changed and got warmer so we get a growth period of life and more forms as more of the hidden potential of the DNA is expressed.
The Magnetostratigraphy its supported also by radiometric dating of rocks.
Our magnetic field may flip but there is a time period when it is flipping and it may be hundreds to thousands of years at near zero. Could we generate our own, it would be a lot of power though.
During this period, the entire planet Earth may have experienced a much higher electrical potential due to solar storms. The geophysical effects of this phenomenon on life are not well understood, but they may have contributed to the emergence of unusual, Frankenstein-like life forms. Increased volcanic activity, particularly in the basaltic mid-ocean ridges, may have been caused by induction heating, along with more oxygen being produced from deep-sea rocks known as polymetallic nodules.
Electromagnetic induction heating as a driver of volcanic activity on massive rocky planets.
https://arxiv.org/abs/2004.14041
https://www.popularmechanics.com/science/environment/a64390388/scientists-find-dark-oxygen/
Supercharging a solar storm
On a regional scale, the underlying geological makeup can have a hugely significant influence on a storm’s damage potential. Sedimentary rocks tend to have pore space that contains water, which makes them electrically conductive, says Ciaran Beggan, a geophysicist with the British Geological Survey. Metamorphic and igneous rocks are denser and less porous and so are more electrically resistive.
But during a geomagnetic storm, errant magnetic activity induces electrical currents at the planet’s surface that can mean trouble for a city built on top of metamorphic or igneous rock. Although the current can’t easily flow through these rocks, “if you’ve short-circuited the insulating part of the earth with a power grid, it flows right through it,” causing damage, Love says.
https://www.nationalgeographic.com/science/article/solar-storms-worse-damage-if-you-live-near-certain-rocks-geology
I would add to the above interesting discussion some more material related to the history of our knowledge in this territory, which I teach in one of my college classes.
The idea that continents drift over time can be traced back to the age of European exploration to speculations of Abraham Ortelius in 1596, and of Francis Bacon, about the similarity of the Atlantic coastlines, especially of Africa and South America, in his Novum Organum, published in 1620. A number of authors published on this idea in the 1800s and the implication that the continents had drifted. Alfred Wegener added to this speculation in greater detail in a paper in 1912, noted that fossil beds facing each other on the Atlantic coastlines were identical and argued for their once having been united. He also coined the name Pangaea for the supercontinent he proposed had existed at a previous time.
That the Earth’s magnetic field changes over time also became well known during the age of European exploration. Sir Edmund Halley can be credited with the first really global scale maps of the Earth’s magnetic field in 1701. He mapped contours of equal magnetic declination, the deviation of the compass needle from the true north direction, as shown by comparison to the stars (called isogonic or declination charts). He collected his data on long voyages around the Atlantic and from the logs of other ships that had sailed world wide. His map can be seen at:
(https://commons.wikimedia.org/wiki/File:Halley_isogonic_1701.jpg)
The declination error in compass North compared to true spin axis North was already known to be changing fairly rapidly in his time and so various countries in Europe and also eventually the US issued updated charts every few years to allow compass north readings to be corrected to true north. A very nice animation of several hundred years worth of charts running from 1590 to 1990 produced by the British Admiralty can be seen at: (https://en.m.wikipedia.org/wiki/File:Earth_Magnetic_Field_Declination_from_1590_to_1990.gif) and (Fig. 8, https://en.wikipedia.org/wiki/Earth%27s_magnetic_field).
I think that the moving distortions of the non-bipolar field declination over time seen in the animation suggests a possible presence of inward projecting relief on the inner surface of the mantle, that distorts the outer core’s smooth circulation.
Maury discovered from soundings in the 1850s that there was a mid-Atlantic ridge and soundings by others in the following decades extended knowledge of it towards the poles. It eventually turned out that it could be seen on the surface on Iceland. For example, see: (https://guidetoiceland.is/travel-iceland/drive/mid-atlantic-ridge). I visited it one winter some years ago and it was very impressive.
In 1957-58 during the International Geophysical Year, several groups dragged magnetometers across the floor of the Atlantic ocean, and found that there were magnetic stripes running parallel to and on both sides of the ridge. Each stripe on one side had a compass north direction parallel to the ridge and adjacent stripes had alternating North directions as they got further from the ridge. The patterns were mirrored on the other side of the ridge. The obvious interpretation was and is that the sea floor was emerging and spreading at the ridge, that the floor-to-be was iron rich, and that while liquid the lava’s magnetic domain particles oriented parallel to the magnetic field of the time, and as they cooled they froze in the field direction. This is still the interpretation.
Dating the fossil layers common to both shores gave a date of about 250 million years ago for the start of the Atlantic Ocean, which puts it back near the beginning of the age of the dinosaurs. This and the present span gave a crude sea-spreading rate of about a few centimeters per year. Recent direct measurements of spreading using radio telescopes looking at a chosen celestial radio source from opposite sides of a crustal plate boundary, watched their change in pointing angle over time, and found the spreading rate to be in that range, . (See: https://ipnpr.jpl.nasa.gov/progress_report2/42-56/56I.PDF)
The field reversals have been modeled based on assuming internal magnetic fields that exist in the liquid metal (mostly iron) in the outer core. (See figure 11, https://en.wikipedia.org/wiki/Earth%27s_magnetic_field). Some of these models show reversals at some of the various time scales.
We might expect to observe magnetic fields around extra-solar planets if they are not gaseous and the spectra of their stars show solar-type elemental abundances, and with those givens expect similar field behavior and life-shielding results.
Bill, thanks so much for this. A wonderful contribution, and with so many leads to follow up. Much appreciated.
I had no idea that the idea of seafloor spreading went back so far. I assumed that the shape of Africa and S. America had to be mapped well for the idea to be formed. That the mounting geological evidence could be dismissed for so long is a tribute to old ideas refusing to accept the evidence.
IDK if it was true, but I thought that the final acceptance of Wegener’s continental drift theory was very much accepted as a Kuhnian paradigm shift. As the old joke goes, old theories die one grave at a time.
Fascinating backstory on this topic.
Like so much of my education after WWII, I was taking my masters in Oceanography in the mid 1070s when Continental Drift was a theory only confirmed a decade or so earlier while I was starting school.
Do you happen to know whether any of the magnetic reversals have been detected in the fossil record of species extinction and appearance?
Fascinating articles and comments, as always :) Here a small complementary paper from the CEA (https://www.cea.fr/english – a french research center) which provides some interesting details on this subject here (sorry the text is in French; I did not find a way to create a link to the translated pdf :/ Google translate translates it well) :
https://www.cea.fr/multimedia/Documents/publications/clefs-cea/archives/fr/MemoD.pdf
Magnetism is generated by the dynamo effect and the movement of the [Earth’s] core. Could a rocky exoplanet with a relatively stable core, and therefore a fairly regular magnetic field, support life ? Should we also look on this side ?
Do we have any idea of the limit value of the magnetic field in Gauss to support life and not destroy it ?