June 10, 2020 | David F. Coppedge

Origin of Geomagnetism: Bumbling in the Dark Past

When did the Earth get its magnetic field? It’s important because life depends on it. Watch MIT fumble and stumble over the question.

Consumers of science news often get triumphant-sounding assertions about things, leading the reader to assume that the experts know what they are talking about. A typical statement might say, ‘The Earth’s magnetic field originated 3.5 billion years ago from a dynamo caused by stirring of molten iron in the Earth’s core, and reverses its polarity in 100,000 year cycles.’ Here’s a sample from Live Science last September, where reporter Stephanie Pappas adds some sugar and spice to fresh expert cud:

This magnetic-field engine, known as a dynamo, has been chugging along for billions of years. Scientists think that the current core arrangement may have settled into place about 1.5 billion years ago, according to 2015 research that found a leap in the magnetic field’s strength around then. But Tarduno and his team have found evidence for a magnetic field on Earth in the planet’s oldest minerals, zircons, dating back 4.2 billion years, suggesting that activity in the core has been creating magnetism for a very long time. 

Content with sound bites from smart scientists, consumers are content to store that knowledge somewhere in their hippocampus and go on with their lives. The astute readers of CEH ask, “How do they know that?” How does anyone look at a zircon and decide when and how geomagnetism started? Asking questions makes science much more interesting and fun! What we shall see is a case of divination and disputation, not one of certitude.

Origins of Earth’s magnetic field remain a mystery (MIT News). One would think that experts at the prestigious Massachusetts Institute of Technology know their geophysics as good as anybody. In this press release, Jennifer Chu used the occasion of disputed readings of zircons from a famous site in Australia to look into the mutterings of geophysics wizards.

Microscopic minerals excavated from an ancient outcrop of Jack Hills, in Western Australia, have been the subject of intense geological study, as they seem to bear traces of the Earth’s magnetic field reaching as far back as 4.2 billion years ago. That’s almost 1 billion years earlier than when the magnetic field was previously thought to originate, and nearly back to the time when the planet itself was formed.

But as intriguing as this origin story may be, an MIT-led team has now found evidence to the contrary. In a paper published today in Science Advances, the team examined the same type of crystals, called zircons, excavated from the same outcrop, and have concluded that zircons they collected are unreliable as recorders of ancient magnetic fields.

Ah, crystals! The perfect tools for divination. Only scientists have the know-how to listen to what they say. Searching the world, geowizards found the best crystals at a site in Australia. Going through accepted rites, they could get them to say, ‘We crystals are 3.5 billion years old.’ But later, another team heard them say, ‘We are 4.2 billion years old.’ Now, the first team of wizards has decided, ‘The zircons aren’t saying anything. They’re dumb, and we’re deaf!’

“There is no robust evidence of a magnetic field prior to 3.5 billion years ago, and even if there was a field, it will be very difficult to find evidence for it in Jack Hills zircons,” says Caue Borlina, a graduate student in MIT’s Department of Earth, Atmospheric, and Planetary Sciences (EAPS). “It’s an important result in the sense that we know what not to look for anymore.

The tale unravels from there. Now that the magic crystals aren’t talking, the press release admits that the wizards had never learned anything about the Earth’s magnetic field from those magic rocks.

  • They don’t know how or why the magnetic field supposedly began 3.5 billion years ago.
  • Their books of magic spells tell them that the core solidified a billion years ago, “meaning that the magnetic field must have been driven by some other mechanism prior to 1 billion years ago.” Really? What was that?
  • “The Jack Hills zircons are some of the most weakly magnetic objects studied in the history of paleomagnetism,” Weiss says. Looks like room for big error bars.
  • “Furthermore, these zircons include the oldest known Earth materials, meaning that there are many geological events that could have reset their magnetic records.
  • The magnetite crystals geophysicists use to measure the field are only the width of a human hair.
  • Only 350 zircons out of 3,754 gathered at Jack Hills ‘dated’ at older than 3.5 billion years.
  • Of those, only three were deemed suitable as “relatively free of impurities” – at least the detectable impurities.
  • Of the three left, only two had magnetite in them.
  • The two had cracks in them where water could have carried in magnetite long after the zircons formed.
  • “We’ve shown that, before 3.5 billion years ago, we still have no idea when Earth’s magnetic field started.

The experts know nothing. They don’t know when the field started. They don’t know how it started.

“For me, these results cast a great deal of doubt on the potential of Jack Hills zircons to faithfully record the palaeomagnetic field intensity prior to 3.5 billion years,” says Andy Biggin, professor of paleomagnetism at the University of Liverpool, who was not involved in the research. “That said, this debate has been raging, like the palaeomagnetic equivalent to Brexit, since 2015 and I would be very surprised if this were the last word on the matter. It is nigh on impossible to prove a negative and neither methods nor interpretations are ever beyond question.

Refreshing, isn’t it, to get away from confident pronouncements from wizards and have them admit they don’t know what they are talking about. Maybe it is time for the public to go Brexit from geo-wizards.

The How Question

Scientists believe that complex currents above the Earth’s iron core as it cools generate a dynamo to create the magnetic field. Notice that they said, “the magnetic field must have been driven by some other mechanism prior to 1 billion years ago.” In other words, they don’t know how magnetic fields are generated, if “some other mechanism” had done it for over twice as long as whatever makes it run now. Starting at 4.2 billion years ago, maybe a field existed. For 2.5 more billion years, “some other mechanism” did it. For the most recent billion years, they ‘think’ a geodynamo did it. Time for a little posturing:

Scientists know that today the Earth’s magnetic field is powered by the solidification of the planet’s liquid iron core. The cooling and crystallization of the core stirs up the surrounding liquid iron, creating powerful electric currents that generate a magnetic field stretching far out into space. This magnetic field is known as the geodynamo.

Do they really know these things? Back in the Live Science article, Pappas hears her expert bring in the Swiss Army Knife of solar system explanations: impacts.

It isn’t clear why the dynamo got started, Tarduno told Live Science, though it’s possible that the enormous planetary impact that created the moon might have been the key driver. This impact, which occurred perhaps 100 million years after Earth came together, could have shaken up any stratification, or layering, of materials in Earth’s core: Imagine shaking up a bottle of oil and water on a planetary scale. This disruption could have promoted the convection that still drives Earth’s dynamo today.

The How Long Question

It’s rare to hear how long the magnetic field can last. Wikipedia‘s article on the geodynamo admits, “The Earth’s magnetic field strength was measured by Carl Friedrich Gauss in 1832 and has been repeatedly measured since then, showing a relative decay of about 10% over the last 150 years.” That’s astonishing. That’s a huge decay in a short time. Later, the entry also admits, “At this rate of decrease, the field would be negligible in about 1600 years.” Not millions of years. Not billions of years. That is a shocking six orders of magnitude less time than geophysicists usually speak of in their moyboy assumptions, but neither the MIT article nor the Live Science article mention this serious issue.

An earlier article by Stephanie Pappas at Live Science (30 April 2018) mentioned the decaying field strength, but simply assumed that decay is followed by increase during magnetic polarity reversals. That is not correct; the polarity changes, but not the intensity. The intensity, or strength, of the field is subject to the Second Law of Thermodynamics, which means that some of the energy is lost as heat to space. There’s no way to get it back without input of more energy from another source. Pappas mentions ‘anomalies’ in the field strength from place to place and time to time, but those are temporary shifts of energy. The overall energy of the field cannot climb higher than it was before.

Dr Richter’s book examines many amazing finely-tuned “coincidences” that make our planet habitable

Dr. Henry Richter devoted a chapter to this problem in his book Spacecraft Earth: A Guide for Passengers (2017). He shows that the Earth’s magnetic field is not a perpetual motion machine: it is doomed to decay, and will continue to decay at the rate measured for 188 years – the longest-running continuous measurement in geophysics.

This is important to us humans for two reasons: (1) Life needs the field to survive, because the field protects life from radiation, and protects the atmosphere from being stripped away. Consequently, life could not last more than a few thousand years into the future, certainly not millions or billions of years. And that implies that we live in a very exceptional time, because over billions of years, why didn’t it already happen? (2) Life could not have existed more than a few tens of thousands of years back in time, because extrapolating the decay rate back in time implies a field strength so powerful, it would have rendered the Earth uninhabitable.

This means that the glib age estimates tossed out by the wizards are wrong. They don’t have their precious Darwin Years to draw on. They cannot make reckless drafts on the bank of time, because the assets are not there. The Earth is young; Darwinism is dead; and now you have heard the world’s greatest wizards on geophysics at MIT admit they don’t know what they are talking about.

 

 

 

 

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