How The Earth Got Its Magnetic Field (And Why It Might Not Protect Us Much Longer)

[Music] the middle of the 19th century saw much of america woven together in an immense interconnected web all in the name of electrical telegraph this cutting-edge technology harnessed electricity for wide-scale communication for the first time in history telegraph offices all over america were connected by fine threads 23 000 miles of electrical cable suspended above the ground on lofty pylons electricity pulsed between offices tapping sounders in an intricate code to be translated into messages by skilled telegraph officers [Music] and on one morning in early september 1859 one such operator noticed something strange as he walked to work along the streets of boston the telegraph cables that looped above began to crackle and buzz in a way he'd never noticed before as he neared his destination the pylons that held them aloft began to sputter and spark even as he leapt up the stairs and burst into the telegraph office a flame of fire jumped from the wires in the room towards his equipment setting a pile of papers nearby ablaze the operator wasting no time tossed the burning pile through the window and rushed to disconnect his equipment from the batteries that powered them the sparking ceased and he collapsed into his chair he still wasn't sure what had caused the strange surge in electricity but with the power disconnected from the equipment the office was safe for now and yet a short while later the telegraph began to gently tap all on its own instinctively the operator grabbed his writing equipment and began to decode the message it was from the telegraph office in portland maine more than 100 miles away their equipment was disconnected too with no power to the stations the two operators communicated back and forth not through the telegraph lines but through the very air itself so charged was the air with electricity that the messages were even clearer than when they traveled through the wires no one had witnessed anything like it before eventually though the electrification of the skies subsided a normal service could resume on the american telegraph but the messages that arrived after told of similar strange happenings all across the country bright auroras as vivid curtains of light were spotted as far south as the caribbean and hawaii making the night skies so bright that birds awoke to begin their dawn chorus at 1am elsewhere aurora's glowed crimson reflecting in the ocean turning it biblical blood red worldwide people saw these signs and wondered if they foretold the end of days our continued existence on this planet suggests that it wasn't in fact the end of days but something very strange did happen that day in 1859 something that has not happened on that magnitude since and to reveal the source of this potentially apocalyptic phenomena and more importantly why it didn't lead to total worldwide annihilation will take a journey from the surface of the sun to the center of the earth and a trip in time from earth's earliest moments to our planets not too distant future [Music] a few hours before the strange happenings in the boston telegraph office on the other side of the atlantic an english amateur astronomer trained his telescope on the noonday sun richard carrington protected his eyes by projecting the image from the telescope onto a white screen he then used that image to track the movement of dark sunspots across the sun's surface this study had been going on for many months but on this day he saw something different two spots of bright light broke out and rapidly grew in intensity they were so bright that carrington thought there was a hole in his screen but as these light patches moved across the surface with their darker companions he soon realized they were coming from the sun itself and yet as rapidly as they had appeared the flashes began to fade they lasted no more than a few minutes and richard carrington just happened to be in the right place at the right time to see them it wasn't too long before the scientific community began to piece together carrington's observations with the global events that followed giving birth to the study of space weather in the process carrington had by chance witnessed a massive solar flare an eruption from the sun's surface with the energy of 10 billion atom bombs the flare sent electrified gas and supercharged electrons streaming towards the earth at some large fraction of the speed of light these super energetic particles have the power to burn and blister skin and damage our very dna causing long-term tissue degradation and pervasive cancer the flare had the potential to life on earth not only that but the magnetic effects of the flare could set up electric currents in any conducting material heating them up and starting catastrophic fires electricity cables could sag and snap any electronic equipment would ionize and short out destroying circuitry through direct or indirect action huge solar flares had the very real potential to bring human civilization as we know it and much of life on earth to its knees eventually repeated flares could even erode the planet's protective ozone layer and atmosphere leaving the earth dry and barren exposed to the deep dark cold of space but they didn't instead in 1859 we were treated to eerie but beautiful light shows and a few minor incidents on the telegraph and that's all thanks to the earth's protective magnetosphere this invisible planetary shield is created by a self-sustaining magnetic field so large that it encompasses the entire planet this magnetic field acts like a vast bubble the strong magnetic forces repel the flare's own magnetic pulses and deflects the damaging solar wind around the planet and out into space but the field withstands the full force of the sun's bombardment and is battered into new shapes in the process sometimes rifts in the planetary shield open for a short time channeling the flare's energy into the earth's atmosphere where it creates dramatic auroras as it ionizes the oxygen and nitrogen in the air but the magnetosphere is self-healing and soon reforms to close these rifts and protect the planet once again in fact it has probably protected the earth from super flares like the one in 1859 for billions of years and yet why it's there and how it works is still something of a mystery [Music] civilizations have been aware of the earth's magnetization for at least 2 000 years lodestones naturally magnetic pieces of rock were known to the chinese in the first century and it was discovered that they would naturally tend to align north to south by the 12th century the chinese song dynasty were using magnetic compasses for navigation knowing that wherever they went the needle would always point north but it wasn't until the 17th century that philosophers and scientists began to contemplate the causes behind this universal rule william gilbert the personal physician to queen elizabeth the first spent his spare time studying magnetism and came to the conclusion that the entire earth behaved like a single gigantic magnet he shaped a lodestone into a sphere called the tetorella and used it to reproduce the angles and tilts of compass needles at different points on the surface studies of the earth's magnetic field have since advanced and we now have precise measurements of the size strength and variations of this gigantic field over time and space and incredibly humans are not alone in their recognition of earth's magnetic field various creatures have even evolved to sense it and respond to it just as we might sense and respond to light or sound or temperature although scientists are still not sure of the precise mechanism birds fish and a range of other animals have been shown to navigate with the help of the earth's magnetic field they can even be thrown off course by small scale fluctuations caused by electrical equipment our knowledge of the interaction between the planetary magnetosphere and living things continues to evolve but a bigger more fundamental mystery still remains what exactly causes this planet-saving planet-sized magnetic field our planet behaves as if it has something like a bar magnet inside of it the magnetic field concentrates at north and south poles near the south and north poles of the planet respectively but there is no immense bar magnet lurking inside the earth geophysicists use the spread of earthquake waves to image the inside of the planet the waves pass faster through dense materials and bounce off boundaries to be reflected back to the surface so we know the earth's interior is a series of nested concentric shells beneath the crust is the semi-solid rock mantle beneath that about 3 000 kilometers deep begins a shell of liquid iron the outer core and deeper still the liquid iron is so compressed that it becomes solid again forming an inner iron core that's bigger than the dwarf planet pluto so no bar magnet but all of that iron filling up nearly half of the earth's insides has magnetic potential and yet not everything that's iron is magnetic to make a planet-wide magnetic shield there must be something else at work and in the early 19th century the self-taught english physicist michael faraday was beginning to formulate a theory on what that something was faraday was an experimentalist and was intrigued by the then recent discovery that electricity movement and magnetism were intimately related he designed the first electric motor which worked by passing an electric current through a wire in a magnetic field making it spin and he reasoned that the same physics could work in a slightly different way that by moving an electrical conductor through a magnetic field an electric current would be created this concept led to the development of the dynamo that uses spinning magnets and coils of wire in elegant armatures to turn mere rotation into electrical power this simple concept is at the root of the electrical generators that produce almost all our power today [Music] but it's not just solid wires and magnets that can power a dynamo faraday theorized that the same principle would work in liquids too and in 1832 he devised an ambitious experiment to test his theory [Music] from london's waterloo bridge he dipped two galvanometers instruments for detecting electricity into the flowing waters of the thames he believed that the motion of the great river through the earth's magnetic field would be enough to generate an electric current within the water sadly his instruments recorded no electricity the chemistry of the languid waters interfered with any voltages that were generated but his theory was sound conductive fluids do behave electromagnetically this is good news for the earth's interior and the generation of its magnetic field a hundred years after faraday's pioneering work german-born physicist walter el sassa suggested that the magnetic field is generated by the dynamo motion of the planet's liquid outer core the inner core is a scorching 6000 degrees celsius while the outer edge of the outer core is cooler around 3000 degrees so heat escapes from the inner core through the liquid metal by means of convection rising and falling plumes of liquid metal that are sheared sideways by the earth's own rotation by extension of the dynamo theory these deep convective currents elsassa supposed were responsible for the planet's magnetosphere a self-exciting geodynamo that sustains and reinforces a magnetic shield that swaddles the entire globe in the last 80 years geophysicists have been able to study the earth's magnetic field in ever-increasing detail and study the fluid motions of this vast body of liquid metal but there is still a surprising amount that we just don't understand we don't know how the heat which drives the convection and the currents in the outer core is generated of course we have no hope of probing the unfathomable depths of the core to find out and without knowing what creates the heat we can't know how it will change in the future or how it will affect the magnetic generation as well as this we don't know the precise motions of the liquid metals in the core that are responsible for generating the magnetic field and we don't know how or when our magnetic field was born it's thought that the solid inner core plays a crucial role in regulating the flow and driving the dynamo but that inner core probably only formed relatively recently in the last billion years or so as the center of the planet cooled enough for the iron to solidify and yet life has persisted for several billion years and there's evidence of a magnetic field preserved in rocks 3.5 billion years old there has been a magnetic shield protecting our planet from solar super flares for far longer than the inner core has been around so how did that early early dynamo work scientists still aren't sure but they do have a good record of how the field has changed over time and what our magnetic future might hold and it doesn't look good the magnetic pole in the northern hemisphere was first pinpointed in 1831 but perhaps surprisingly it wasn't located at the rotational north pole but rather in northern canada some 2000 kilometers south since then the magnetic pole has wandered across the surface of the planet heading north and west today it lies over the arctic ocean just 500 kilometers off true north this wandering is the result of the fluid dynamo deep within the planet as the currents shift and shear so the field it produces wanders incredibly scientists can even trace these changes of the magnetic field back through many million years of geological time too lava that erupts at the surface contains iron-rich minerals while the rocks are liquid those minerals feel the tug of the earth's magnetic field and align themselves towards the pole like tiny compasses then when the rocks cool and solidify those alignments are frozen in place by measuring their orientations today we can reconstruct the movements of the rock and the poles over vast spans of our earth's history and magnetostratigraphy has helped us map the movement of continents across the planet's surface but also reveals something remarkable about our magnetic field by measuring the alignments of magnetic materials at the bottom of the atlantic ocean a strange pattern emerges stripes parallel with the mid-atlantic ridge in which the rock compasses alternate pointing north and south and north and south with the stripes mirrored on either side of the central ridge there can be only one explanation for this curious pattern the entire magnetic field switches flip-flopping from north to south and back again over periods of millions of years these so-called magnetic reversals are seen in rocks all over the globe and it's now clear that this magnetic flip-flopping is a consistent feature of our planetary shield they happen at random times sometimes staying the same for 40 million years sometimes switching every 200 000 years but these reversals don't happen instantaneously records show that it takes several thousand years for north and south to switch during which time the magnetic bubble around the planet would become messy and distorted with no clear pole to point to compasses would become useless auroras which are the result of the solar wind being channeled along the field lines would be seen all over the globe not just at the poles but more worryingly with the magnetosphere so twisted and diminished it would leave the earth exposed to that solar wind putting life on the planet at risk in the event of a powerful superflare although it has never yet happened in the history of human civilization there are signs that things are beginning to change [Music] the wanderings of the poll have accelerated in the last 40 years and it is now moving across the arctic ocean at a breakneck speed of about 55 kilometers a year at the same time it seems that the overall geomagnetic intensity has dropped by 35 percent over the last two millennia as the protective magnetosphere bubble shrinks towards the planet's surface seeing these changes over our lifetime reveals just how critical the magnetic field is to our continuing existence if a superflare like the one that raced towards the earth in 1859 happened again today or in the future we would find ourselves a lot more vulnerable to its damaging radiation with a weaker magnetic field we couldn't say for certain how well it would withstand the assault at the same time we have been putting ever more reliance on our electrical infrastructure even placing much of it in orbit around the planet for the sake of global connectivity electronic equipment placed at the edge of an already shrinking magnetic shield is especially vulnerable a superflare could penetrate the planet's defenses fry the electronics beyond repair and bring global communications to its knees intense magnetic pulses could wipe clean digital records destroying our history as well as our present this time it actually could be the end of days and so it is a sobering thought that this invisible shield created by processes we don't fully understand in layers of the earth beyond our reach might just be the key to our survival up here on the delicate surface of earth next time we will explore what earth was like three billion years ago and the incredible story of the planet's first mass extinction you've been watching the entire history of the earth like and subscribe and leave a comment to tell us what you'd like to see covered next thanks for watching and we'll see you next time

Channel: History of the Earth

Views: 228,614

Rating: 4.9006023 out of 5

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Id: 9CSGOtEnEnI

Length: 23min 20sec (1400 seconds)

Published: Sun Oct 11 2020

Reddit Comments

[u/engakuis]

I'm just curious why you posted this?