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  • richardmitnick 6:57 am on August 25, 2020 Permalink | Reply
    Tags: "The Age of the Earth’s Inner Core Revised", , Earth's Magnetic field, , Measuring the conductivity of iron under corelike conditions., Researchers have improved the estimate of the age of our planet’s solid inner core putting it at 1 billion to 1.3 billion years old., The Earth’s core is made mostly of iron with the inner core being solid and the outer core being liquid., The geodynamo was maintained by two different energy sources and mechanisms: thermal convection and compositional convection.,   

    From University of Texas at Austin: “The Age of the Earth’s Inner Core Revised” 

    U Texas Austin bloc

    Aug 21, 2020
    Monica Kortsha
    Jackson School of Geosciences

    A computer simulation of the Earth’s magnetic field, which is generated by heat transfer in the Earth’s core. NASA/ Gary A. Glatzmaier.

    By creating conditions akin to the center of the Earth inside a laboratory chamber, researchers have improved the estimate of the age of our planet’s solid inner core, putting it at 1 billion to 1.3 billion years old.

    The results place the core at the younger end of an age spectrum that usually runs from about 1.3 billion to 4.5 billion years, but they also make it a good bit older than a recent estimate of only 565 million years.

    What’s more, the experiments and accompanying theories help pin down the magnitude of how the core conducts heat, and the energy sources that power the planet’s geodynamo — the mechanism that sustains the Earth’s magnetic field, which keeps compasses pointing north and helps protect life from harmful cosmic rays.

    “People are really curious and excited about knowing about the origin of the geodynamo, the strength of the magnetic field, because they all contribute to a planet’s habitability,” said Jung-Fu Lin, a professor at The University of Texas at Austin’s Jackson School of Geosciences who led the research.

    The results were published on Aug.13 in the journal Physical Review Letters.

    The Earth’s core is made mostly of iron, with the inner core being solid and the outer core being liquid. The effectiveness of the iron in transferring heat through conduction — known as thermal conductivity — is key to determining a number of other attributes about the core, including when the inner core formed.

    Over the years, estimates for core age and conductivity have gone from very old and relatively low, to very young and relatively high. But these younger estimates have also created a paradox, where the core would have had to reach unrealistically high temperatures to maintain the geodynamo for billions of years before the formation of the inner core.

    The new research solves that paradox by finding a solution that keeps the temperature of the core within realistic parameters. Finding that solution depended on directly measuring the conductivity of iron under corelike conditions — where pressure is greater than 1 million atmospheres and temperatures can rival those found on the surface of the sun.

    The researchers achieved these conditions by squeezing laser-heated samples of iron between two diamond anvils. It wasn’t an easy feat. It took two years to get suitable results.

    “We encountered many problems and failed several times, which made us frustrated, and we almost gave up,” said article co-author Youjun Zhang, an associate professor at Sichuan University in China. “With the constructive comments and encouragement by professor Jung-Fu Lin, we finally worked it out after several test runs.”

    The newly measured conductivity is 30% to 50% less than the conductivity of the young core estimate, and it suggests that the geodynamo was maintained by two different energy sources and mechanisms: thermal convection and compositional convection. At first the geodynamo was maintained by thermal convection alone. Now, each mechanism plays about an equally important role.

    Lin said that with this improved information on conductivity and heat transfer over time, the researchers could make a more precise estimate of the age of the inner core.

    “Once you actually know how much of that heat flux from the outer core to the lower mantle, you can actually think about when did the Earth cool sufficiently to the point that the inner core starts to crystalize,” he said.

    This revised age of the inner core could correlate with a spike in the strength of the Earth’s magnetic field as recorded by the arrangement of magnetic materials in rocks that were formed around this time. Together, the evidence suggests that the formation of the inner core was an essential part of creating today’s robust magnetic fields.

    The National Science Foundation and the National Natural Science Foundation of China supported the research.

    The research team also included Mingqiang Hou, Guangtao Liu and Chengwei Zhang of the Center for High Pressure Science and Technology Advanced Research in Shanghai; Vitali Prakapenka and Eran Greenberg of the University of Chicago; and Yingwei Fei and R.E. Cohen of the Carnegie Institution for Science.


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    U Texas at Austin

    U Texas Austin campus

    In 1839, the Congress of the Republic of Texas ordered that a site be set aside to meet the state’s higher education needs. After a series of delays over the next several decades, the state legislature reinvigorated the project in 1876, calling for the establishment of a “university of the first class.” Austin was selected as the site for the new university in 1881, and construction began on the original Main Building in November 1882. Less than one year later, on Sept. 15, 1883,

  • richardmitnick 11:03 am on July 10, 2017 Permalink | Reply
    Tags: , , Earth's Magnetic field, eGaIn a liquid alloy of indium and gallium, Magnetic Liquid Metals, The Earth's liquid outer core made of iron is crucial to creating Earth’s magnetic field, University of Maryland Three Meter dynamo experiment,   

    From Yale: “Study of the Center of the Earth” 

    Yale University bloc

    Yale University

    June 30, 2017
    Sonia Wang

    Study of the Center of the Earth | Yale Scientific

    What would you do with two million dollars? Chances are dim that your first answer would be to build and buy enough liquid sodium to fill a three-meter radius spherical tank. But for some scientists, this investment—the University of Maryland Three Meter dynamo experiment—paid off, serving as a key step to understanding the age-old question of how Earth’s magnetic field is generated.

    Earth’s magnetic field not only shields us from the sun’s damaging radiation, but also helps us navigate the Earth. Geophysicists have long studied the magnetic field created by Earth’s liquid core, but attempts to re-create them in the lab have previously been unsuccessful due to the prohibitively high costs of building equipment to do so.

    However, in a study published in January[Physical Review Fluids], a team of Yale researchers in Mechanical Engineering Professor Eric Brown’s lab developed a method for producing liquid metal with improved magnetic properties. The researchers created a protocol to create these Magnetic Liquid Metals (MLM) after studying a suspension of magnetic iron particles in eGaIn, a liquid alloy of indium and gallium. Such a technique could enable researchers to conduct dynamo experiments, which model the generation of Earth’s magnetic field, on a far smaller size scale.

    Magnetic Field’s Liquid Beginnings

    By studying earthquakes as they travel through the planet, seismologists know that the Earth has a fluid outer core surrounding a solid iron inner core. The liquid outer core, made of iron, is crucial to creating Earth’s magnetic field and is an example of a magnetohydrodynamic (MHD) phenomenon—magnetic properties resulting from an electrically conductive fluid. Movement of the outer core in the presence of Earth’s magnetic field induces electrical currents, which then create their own magnetic field aligning with Earth’s overall magnetic field. This process sustains itself and allows for the maintenance of Earth’s magnetic field over the years.

    The Earth’s magnetic field is responsible for phenomenon such as the Northern Lights, which occurs when the sun’s radiation is deflected by the magnetic field and collides with atmospheric particles. Image courtesy of Kristian Pikner, Wikimedia Commons.

    Magnetohydrodynamic phenomena only occur at a high magnetic Reynolds number, which describes the magnetohydrodynamic properties of an object; at a high Reynolds number, MHD phenomena are more likely. The magnetic Reynolds number depends on several properties, such as the system size, the fluid velocity, electrical conductivity, and magnetic susceptibility—the response of the fluid to a magnetic influence. Something as large as a planet would have an extremely high Reynolds number, making MHD phenomena more natural. However, re-creating such phenomena in a laboratory setting is extremely difficult, requiring materials with high magnetic and electrical properties.

    Traditional studies of MHD have used liquid metals and plasmas because they have the highest electric conductivities of any known materials. Liquid sodium has the highest conductivity and has been used to create a dynamo experiment in the past, but is both expensive and dangerous; sodium reacts explosively with water and needs to be heated above its high melting temperature. Looking for a safer and easier alternative, the researchers sought to use a different liquid metal base for the study.

    However, as noted before, other factors such as the magnetic susceptibility also affect the Reynolds number. Despite having a good electrical conductivity, pure eGaIn has a low magnetic susceptibility and therefore a low Reynolds number. To boost the Reynolds number, the researchers proposed creating a new material by suspending magnetic particles in liquid metals to increase their magnetic susceptibility and take advantage of the liquid metals natural high conductivity.

    Acid’s Key Role

    While scientists have previously attempted to suspend magnetic particles in liquid metals, they have not been very successful because of metallic oxidation. The oxidation of the metal causes a new “rusted” oxidation layer on the liquid metal, with its own set of properties. As this layer is more solid, it prevents some of the delicate suspension effects.

    eGaIn shows stronger magnetic properties than liquid sodium. Image courtesy of Florian Carle.

    Initially, stirring iron particles into the liquid eGaIn failed to create a successful suspension, since a solid oxide layer formed at the surface of the liquid upon exposure to air. Despite vigorous stirring to break the oxide skin, the particles clung to the oxide skin due to the strength of the interactions between the two layers.

    Seeking solutions to this problem, the scientists used hydrochloric acid (HCl), at a dangerously low pH of 0.69 capable of corroding skin, as a chemical cleaner or purifying agent; in eGaIn, hydrochloric acid removes the oxide layer on the liquid metal and iron particles, allowing for more liquid-like properties in the metal and increasing the conductivity of the iron particles. The suspension process was successful after the researchers added enough HCl to cover the metals and prevent further contact with air.

    Design Your Own Fluid

    The new material has increased magnetohydrodynamic properties compared to the original eGaIn. The resulting MLM had a Reynolds number over 5 times higher than that of pure liquid metal, or two times higher than liquid sodium. Thus, a dynamo experiment that would previously have required a three-meter radius tank might be possible on a much smaller size scale—10 square centimeters rather than three meters. “Until this study, no one thought about doing dynamo experiments with eGaIn because the quantity needed for these experiments make it cost prohibitive,” said Florian Carle, the lead author of the paper.

    Furthermore, certain properties of the MLM can be customized for different purposes and different applications. As long as the conductivity of the iron particles you would like to suspend is higher than that of the liquid metal base, nearly any material can be used for the liquid and suspended particles. “It’s basically Design Your Own Fluid…you can suspend silver, graphene, diamond…you can tune the size of the particles within this huge range,” Carle said. Changing the quantity of iron particles in eGaIn will modify the material viscosity—the more particles, the more viscous the fluid. Furthermore, changing the type of particle used can further affect the conductivity and magnetic properties of the material; using highly conductive particles will increase conductivity, and using magnetic particles like iron or steel can increase magnetic properties.

    The applications are myriad. Separately controlling the viscosity and the magnetic properties of the material will allow scientists to isolate the effects of magnetohydrodynamics, which is indicated by the Reynolds number, and turbulence, a measure affected by fluid viscosity and velocity that indicates how chaotic the flow of the material is.

    Carle designed the paper to be easily accessible, so that even a scientist without special training could re-create the material. He hopes that more scientists will apply the procedure to their research: “Now that we can tune the properties…hopefully people will start picking up on that and be able to use that. I hope in the near future we will see more and more experiments using MLMs,” Carle said.

    Of Sustainability and Superfluids

    Though Carle has moved on to work at the Yale Quantum Institute, research continues in the Brown lab on the material. One challenge the group is investigating is in keeping the magnetic liquid metals fresh during storage: after six months of storage, samples exhibited a loss in magnetic susceptibility as the hydrochloric acid slowly ate away at the iron particles.

    “It’s a bit of a conflict, since you need to protect the eGaIn with HCl, but then the HCl will eat the iron,” Carle said. Further research is being done to develop storage methods for eGaIn, including solidifying the samples or removing HCl to allow formation of a protective oxide layer on the surface of the fluid during storage.

    Carle further speculates that there are applications beyond MHD and dynamo experiments, since it is a customizable new material. And perhaps an MLM could eventually be created out of sodium, which has the highest electric conductivity of any known liquid metal. Adding magnetic particles to that suspension could allow scientists to attain a Reynolds number off the charts. “You would have a superfluid…maybe we would see phenomena we haven’t seen anywhere before,” Carle said.

    Featured Art by Isa del Toro Mijares

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  • richardmitnick 7:49 am on March 23, 2017 Permalink | Reply
    Tags: , , , , , Earth's Magnetic field, , Swarm detects asymmetry   

    From ESA: “Swarm detects asymmetry” 

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    European Space Agency

    22 March 2017

    Title Swarm
    Released 23/03/2012 1:18 pm
    Copyright ESA/AOES Medialab
    Swarm is ESA’s first constellation of Earth observation satellites designed to measure the magnetic signals from Earth’s core, mantle, crust, oceans, ionosphere and magnetosphere, providing data that will allow scientists to study the complexities of our protective magnetic field.

    Strong electric currents in the upper atmosphere are known to vary according to the season, but ESA’s Swarm mission has discovered that this seasonal variation is not the same in the north and south polar regions.

    Named after Kristian Birkeland, the scientist a century ago who first postulated that the ‘northern lights’ were linked to electrically charged particles in the solar wind, these currents flow along Earth’s magnetic field lines in the polar regions.

    Magnetic field measurements from ESA’s Swarm satellite constellation are allowing scientists to understand more about these powerful currents, which carry up to 1 TW of electric power to the upper atmosphere. This is about 30 times the energy consumed in New York during a heatwave.

    Title Seasonal asymmetry
    Released 22/03/2017 10:24 am
    Copyright DTU/BCSS
    Three years of measurements from ESA’s Swarm mission have be combined with measurements from Germany’s earlier Champ satellite to produce global climatological maps of Birkeland currents. These currents tend to be weak for a northwards interplanetary field and strong for a southwards field. Importantly, these new results also reveal that the strength of the currents is not the same in both hemispheres. These hemispheric differences may relate to asymmetry in Earth’s main magnetic field.

    It is important to understand the interplay between these Birkeland currents and the solar wind that bombards our planet and that can potentially cause power and communication blackouts.

    New findings, presented this week at the Swarm science meeting in Canada, show how three years of measurements from the mission were combined with measurements from Germany’s earlier Champ satellite to produce global climatological maps of these currents.

    Title Earth’s protective shield
    Released 06/02/2014 2:09 pm
    Copyright ESA/ATG medialab
    The magnetic field and electric currents in and around Earth generate complex forces that have immeasurable impact on every day life. The field can be thought of as a huge bubble, protecting us from cosmic radiation and charged particles that bombard Earth in solar winds.

    Moreover, these results show differences between currents in the northern and southern hemisphere, how they change with the season and how they vary according to the strength of the solar wind.

    Karl Laundal, from the Birkeland Centre for Space Science, explained, “Interaction between Earth’s magnetic field and the interplanetary magnetic field – meaning part of the Sun’s magnetic field carried by solar wind – depends on how the interplanetary field is orientated.

    “While this sounds complicated, it means that hardly any solar wind can enter the magnetosphere and arrive at Earth if the interplanetary magnetic field points north, parallel to Earth’s magnetic field.

    “On the other hand, if the interplanetary field points south, the opposite is true and this allows a connection to be made with Earth’s magnetic field.

    “Part of the energy in solar wind then further energises the charged particles that are responsible for the visible light displays of the auroras.”

    Birkeland currents therefore tend to be weak for a northwards interplanetary field and strong for a southwards field.

    Importantly, these new results also reveal that the strength of the currents is not the same in both hemispheres. These hemispheric differences may relate to asymmetry in Earth’s main magnetic field.

    In fact, the two geomagnetic poles are not geometrically opposite to one another, and the magnetic field intensity is also not the same in the north as in the south.

    Dr Laundal said, “The main reason for this probably has to do with differences in Earth’s main field. Such differences imply that the ionosphere–magnetosphere coupling is different in the two hemispheres.

    “In particular, the magnetic pole is more offset with respect to the geographic pole in the south compared to north, which leads to different variations in sunlight in the ‘magnetic hemispheres’. Because of these differences, the two hemispheres do not respond symmetrically to solar wind driving or changing seasons.

    “Swarm is a fantastic tool for space science studies. The high-quality measurements and the fact that there are three satellites working in concert hold many new clues about how our home planet interacts with the space around it. It’s a fascinating time.”


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    The European Space Agency (ESA), established in 1975, is an intergovernmental organization dedicated to the exploration of space, currently with 19 member states. Headquartered in Paris, ESA has a staff of more than 2,000. ESA’s space flight program includes human spaceflight, mainly through the participation in the International Space Station program, the launch and operations of unmanned exploration missions to other planets and the Moon, Earth observation, science, telecommunication as well as maintaining a major spaceport, the Guiana Space Centre at Kourou, French Guiana, and designing launch vehicles. ESA science missions are based at ESTEC in Noordwijk, Netherlands, Earth Observation missions at ESRIN in Frascati, Italy, ESA Mission Control (ESOC) is in Darmstadt, Germany, the European Astronaut Centre (EAC) that trains astronauts for future missions is situated in Cologne, Germany, and the European Space Astronomy Centre is located in Villanueva de la Cañada, Spain.

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  • richardmitnick 12:29 pm on June 24, 2016 Permalink | Reply
    Tags: , , Earth's Magnetic field   

    From Carnegie: “What did Earth’s ancient magnetic field look like?” 

    Carnegie Institution for Science
    Carnegie Institution for Science

    June 24, 2016
    Peter Driscoll

    New work from Carnegie’s Peter Driscoll suggests Earth’s ancient magnetic field was significantly different than the present day field, originating from several poles rather than the familiar two. It is published in Geophysical Research Letters.

    An illustration of ancient Earth’s magnetic field compared to the modern magnetic field, courtesy of Peter Driscoll.

    Earth generates a strong magnetic field extending from the core out into space that shields the atmosphere and deflects harmful high-energy particles from the Sun and the cosmos. Without it, our planet would be bombarded by cosmic radiation, and life on Earth’s surface might not exist. The motion of liquid iron in Earth’s outer core drives a phenomenon called the geodynamo, which creates Earth’s magnetic field. This motion is driven by the loss of heat from the core and the solidification of the inner core.

    Magnetosphere of Earth, original bitmap from NASA. SVG rendering by Aaron Kaase
    Magnetosphere of Earth, original bitmap from NASA

    But the planet’s inner core was not always solid. What effect did the initial solidification of the inner core have on the magnetic field? Figuring out when it happened and how the field responded has created a particularly vexing and elusive problem for those trying to understand our planet’s geologic evolution, a problem that Driscoll set out to resolve.

    Here’s the issue: Scientists are able to reconstruct the planet’s magnetic record through analysis of ancient rocks that still bear a signature of the magnetic polarity of the era in which they were formed. This record suggests that the field has been active and dipolar—having two poles—through much of our planet’s history. The geological record also doesn’t show much evidence for major changes in the intensity of the ancient magnetic field over the past 4 billion years. A critical exception is in the Neoproterozoic Era, 0.5 to 1 billion years ago, where gaps in the intensity record and anomalous directions exist. Could this exception be explained by a major event like the solidification of the planet’s inner core?

    In order to address this question, Driscoll modeled the planet’s thermal history going back 4.5 billion years. His models indicate that the inner core should have begun to solidify around 650 million years ago. Using further 3-D dynamo simulations, which model the generation of magnetic field by turbulent fluid motions, Driscoll looked more carefully at the expected changes in the magnetic field over this period.

    “What I found was a surprising amount of variability,” Driscoll said. “These new models do not support the assumption of a stable dipole field at all times, contrary to what we’d previously believed.”

    His results showed that around 1 billion years ago, Earth could have transitioned from a modern-looking field, having a “strong” magnetic field with two opposite poles in the north and south of the planet, to having a “weak” magnetic field that fluctuated wildly in terms of intensity and direction and originated from several poles. Then, shortly after the predicted timing of the core solidification event, Driscoll’s dynamo simulations predict that Earth’s magnetic field transitioned back to a “strong,” two-pole one.

    “These findings could offer an explanation for the bizarre fluctuations in magnetic field direction seen in the geologic record around 600 to 700 million years ago,” Driscoll added. “And there are widespread implications for such dramatic field changes.”

    Overall, the findings have major implications for Earth’s thermal and magnetic history, particularly when it comes to how magnetic measurements are used to reconstruct continental motions and ancient climates. Driscoll’s modeling and simulations will have to be compared with future data gleaned from high quality magnetized rocks to assess the viability of the new hypothesis.

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  • richardmitnick 4:21 pm on December 18, 2015 Permalink | Reply
    Tags: , Earth's Magnetic field, ,   

    From SA: “Magnetic Mystery of Earth’s Early Core Explained” 

    Scientific American

    Scientific American

    December 18, 2015
    Alexandra Witze

    Yuri_Arcurs ©iStock.com

    Geophysicists call it the new core paradox: They can’t quite explain how the ancient Earth could have sustained a magnetic field billions of years ago, as it was cooling from its fiery birth.

    Now, two scientists have proposed two different ways to solve the paradox. Each relies on minerals crystallizing out of the molten Earth, a process that would have generated a magnetic field by churning the young planet’s core. The difference between the two explanations comes in which particular mineral does the crystallizing.

    Silicon dioxide is the choice of Kei Hirose, a geophysicist at the Tokyo Institute of Technology who runs high-pressure experiments to simulate conditions deep within the Earth. “I’m very confident in this,” he reported on December 17 at a meeting of the American Geophysical Union in San Francisco, California.

    But David Stevenson, a geophysicist at the California Institute of Technology in Pasadena, says that magnesium oxide — not silicon dioxide—is the key to solving the problem. In unpublished work, Stevenson proposes that magnesium oxide, settling out of the molten early Earth, could have set up the buoyancy differences that would drive an ancient geodynamo.

    The core paradox arose in 2012, when several research teams reported that Earth’s core loses heat at a faster rate than once thought. More heat conducting away from the core means less heat available to churn the core’s liquid. That’s important because some studies suggest Earth could have had a magnetic field more than 4 billion years ago—just half a billion years after it coalesced from fiery debris swirling around the newborn Sun. “We need a dynamo more or less continuously,” Peter Driscoll, a geophysicist at the Carnegie Institution for Science in Washington DC, said at the meeting.

    In his Tokyo laboratory, Hirose put different combinations of iron, silicon and oxygen into a diamond anvil cell and squeezed them to produce extraordinarily high pressures and temperatures—sometimes above 4,000 ºC—to simulate the hellish conditions of Earth’s interior. He found that silicon and oxygen crystallized out together, as silicon dioxide, whenever both were present.

    When silicon dioxide precipitated in the early Earth, it would have made the remaining melt buoyant enough to continue rising, thus setting up the churning motion needed to sustain the dynamo, Hirose reported. “As far as I know, this is the most feasible mechanism to drive the geodynamo,” he said.

    Stevenson, in contrast, plumps for magnesium, saying it “makes much more sense” than silicon dioxide because magnesium oxide would precipitate out of a molten Earth first. Hirose, he says, “is telling you something that can happen, not what did happen.”

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  • richardmitnick 7:20 am on August 10, 2015 Permalink | Reply
    Tags: , , Earth's Magnetic field,   

    From Cosmos: “Earth’s early magnetic field locked in 4.2 billion-year-old crystals” 

    Cosmos Magazine bloc


    10 Aug 2015
    Belinda Smith

    An artist’s depiction of Earth’s magnetic field deflecting high-energy protons from the Sun four billion years ago (not to scale).Credit: Michael Osadciw / University of Rochester.

    Like tiny compasses frozen in time, ancient zircon gems from Western Australia have shown Earth’s magnetic field is at least four billion years old – more than 700 million years older than previous evidence suggested. Because the magnetic field protects the Earth’s atmosphere from destructive solar rays, it raises the possibility that life could have made its debut much earlier than previously thought.

    A North American team, led by John Tarduno at New York’s University of Rochester, found the young Earth had a chaotic magnetic field that was, at times, as strong as our field today. They reported their work in Science in July.

    It’s “astonishing to be able to probe the magnetic field that far back”, says Louis Moresi, a geoscientist at the University of Melbourne.

    Earth formed some 4.5 billion years ago, accreting from dust and proto-planetary fragments swirling around the Sun. Even in the near absolute zero temperatures of space, enough heat was trapped in the colliding mass to melt material in its core. Over time, the radioactive decay of uranium and other ‘hot’ elements has kept the core molten.

    Today, if you were to drill through the crust, you’d travel through 2,900 kilometres of rocky mantle before reaching the outer core. You’d then slither through 2,200 kilometres of liquid iron, before hitting a metallic inner core about 1,200 kilometres in diameter – a little smaller than the Moon. The inner core is kept solid by the enormous pressures at the centre of the Earth.

    It’s the liquid outer core, constantly stirred by convection currents, that generates our magnetic field. Just as hot air rises, hot iron rises towards Earth’s cooler surface, carrying heat that escapes through the mantle and crust. As the iron cools, it sinks, providing a constant stirring motion that generates our magnetic field.

    The mantle layer is vital to maintaining this motion. If it is too thin, the heat in the core dissipates quickly, along with the magnetic field. If it is too insulating, the vital convection currents shut down.

    Thanks to the Earth’s daily rotation and the stabilising solid inner core, the convection currents in the molten outer core have settled into spiralling columns that lie parallel to the Earth’s axis, giving us the elegant north-south dipole our compasses use today. What was it like in the Earth’s youth?

    It’s hard to say. Our dynamic planet’s surface is continually crushed, stretched and recycled – thanks to plate tectonics – and rock remnants from the Earth’s earliest days are scarce.

    The tectonic plates of the world were mapped in the second half of the 20th century.

    But thanks to a zircon crystal dug out of 4.4-billion-year-old sandstone on a Western Australian sheep ranch, we may have a clue. The University of Wisconsin-Madison-led study last year claimed the gemstone was born 100 million years after the Earth itself.

    For Tarduno and his team, that report raised an exciting possibility. They realised that like mosquitoes in amber, tiny iron oxide grains also known as magnetite would be trapped inside the zircon as it solidified and could have recorded the ancient magnetic field. His team returned to the same area and collected 25 zircon crystals dated from 3.3 to 4.2 billion years old, and examined them for microscopic magnetite flakes. But a super-sensitive instrument was needed to pick out the magnetic alignment in the grains.

    Enter the superconducting quantum interference device (the SQUID).

    SQUID superconducting quantum interference device

    This ultra-high-definition magnetometer can detect faint magnetic fields – as much as 100 billion times weaker than the energy needed to move a compass needle. The SQUID found the magnetite grains harboured magnetic fields of varying strengths – from the equivalent of today’s magnetic field, to 12% of its strength.

    A 4.4 billion-year-old zircon crystal from the Jack Hills region of Western Australia, which is the oldest bit of the Earth’s crust.Credit: John Valley

    Before this study, the oldest evidence for a magnetic field on Earth came from South African rocks dated at 3.2 and 3.45 billion years old. Two of the oldest zircons in Tarduno’s study were 750 million years older. “It’s amazing what they could get out of these little guys,” Moresi says, adding they really are “miracle crystals”.

    So why does the age of the magnetic field affect life’s appearance on Earth?

    Basically, the field shields us from our life-giver – the Sun. Streams of charged particles flow from the Sun, bombarding the inner planets and stripping away their water and atmosphere – unless a magnetic field is strong enough to deflect the onslaught.

    Tarduno points to our neighbour, Mars. The barren world once had a magnetic field, but no longer – nor any surface liquid water or atmosphere to speak of. Scientists think that around four billion years ago the Earth and Mars were battered by asteroids. On Mars, the onslaught over-heated its mantle. As the heat gradient between the core and mantle was lost, its core’s convection currents slowed and eventually stopped, switching off its magnetic shield and allowing the solar wind to whisk its atmosphere away. “It may also be a major reason why Mars was unable to sustain life,” he says.

    But the Earth was a little larger, and able to weather the storm. Ensconced in its protective magnetic bubble, life could begin to flourish.

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