Earth tipped on its side (and back again) 84 million years ago

Earth has not always been upright. Turns out, the planet’s crust tipped on its side and back again around 84 million years ago, in a phenomenon that researchers have dubbed a “cosmic yo-yo.”

The actual name for the tipping is true polar wander (TPW), which occurs when the outer layers of a planet or moon move around its core, tilting the crust relative to the object’s axis. Some researchers had previously predicted that TPW occurred on Earth late in the Cretaceous period, between 145 million and 66 million years ago, but that was hotly debated, according to a statement by the researchers.

However, the new study strongly suggests TPW did occur on Earth. Researchers mapped the ancient movement of Earth’s crust by looking at magnetic-field data trapped inside ancient fossilized bacteria. They found that the planet tilted 12 degrees relative to its axis around 84 million years ago, before fully returning to its original position over the next 5 million years.

This observation represents the most recent large-scale TPW documented and challenges the notion that the [Earth’s] spin axis has been largely stable over the past 100 million years,” the researchers wrote in their paper, published online June 15 in the journal Nature Communications.

Cosmic yo-yo

Earth is made out of four main layers: the solid inner core, the liquid outer core, the mantle and the crust. During TPW, the entire planet would appear turned over on its side, but in reality only the outermost layers have moved.

Imagine looking at Earth from space, TPW would look like the Earth tipping on its side,” co-author Joe Kirschvink, a geobiologist at the Tokyo Institute of Technology in Japan and a professor at the California Institute of Technology, said in the statement. “What’s actually happening is that the whole rocky shell of the planet [the mantle and crust] is rotating around the liquid outer core.

Image: Victor C. Tsai / Wikimedia Commons

Individual pieces of Earth’s outermost layers are constantly moving and changing as tectonic plates collide together and subduct underneath one another; but during TPW, the outer layers move together as a single unit.

As a result, the tilt in Earth’s crust would not have resulted in any major tectonic activity or drastic changes to major ecosystems. Instead, it would have been a gradual process that would not have impacted the dinosaurs and other living things walking around on the surface.

Earth’s electromagnetic field would have been static during the TPW because it is created by the liquid inner core, which would have stayed in place. So rather than the magnetic poles moving, it is the geographic poles that start to wander.

Fossilized magnets

To test if Earth did undergo TPW during the Cretaceous, the researchers turned to magnetic minerals within limestone deposits in Italy.

These Italian sedimentary rocks turn out to be special and very reliable because the magnetic minerals are actually fossils of bacteria that formed chains of the mineral magnetite,” co-author Sarah Slotznick, a geobiologist at Dartmouth College in New Hampshire, said in the statement.

Image: Ross Mitchell / Tokyo Institute of Technology

Magnetite is a highly magnetic form of iron-oxide. Some types of bacteria can create chains of tiny magnetite crystals, which naturally orient with Earth’s magnetic field at the time of their creation. When these particular bacteria died and were fossilized during the period of TPW, these magnetite chains got locked in place.

Because Earth’s crust moved during TPW, and not its magnetic field, these magnetic fossils (which remained in surface layers of the planet) revealed how much the crust moved relative to Earth’s magnetic field over time. The team found that Earth’s crust moved a total of almost 25 degrees over a period of 5 million years.

The researchers believe that their findings now settle the question of whether Earth had a TPW during the Cretaceous.

It is so refreshing to see this study with its abundant and beautiful paleomagnetic data,” Richard Gordon, a geophysicist at Rice University in Houston who was not involved in the study, said in the statement.

See more here: livescience.com

Header image: Getty Images

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Comments (5)

  • Avatar

    Just Me

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    Now the world is upside down.

    Reply

  • Avatar

    Jerry Krause

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    Hi PSI Readers,

    We read: ““This observation represents the most recent large-scale TPW documented and challenges the notion that the [Earth’s] spin axis has been largely stable over the past 100 million years,” the researchers wrote in their paper, published online June 15 in the journal Nature Communications.””

    But before this we read: “However, the new study strongly suggests TPW did occur on Earth.”

    “This OBSERVATION” versus “STRONGLY SUGGESTS”. We understand that 100 millions years there were no humans with the ability to observe magnetic fields.

    What we should KNOW is that we are reading ABOUT WILD CONJECTURE (GUESSES, THEORIES). We are expected to BELIEVE that bacteria existed a 100 million years ago. Assumptions upon assumptions!!! How stupid am I??? Which is a title of one of my essays published here at PSI. Try using the PSI search tool to find this essay. It might work.

    Have a good day, Jerry

    Reply

  • Avatar

    Koen Vogel

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    There are a few concerns I have with the information presented here:
    1) The researchers determine that the geographic pole (True Pole) has moved relative to the magnetic pole, but how can they determine which is moving? It is known that the magnetic pole wanders: the North magnetic pole has been measurably wandering 50+ km/a towards Siberia for the past few years. The geologic record provides numerous examples of magnetic reversals (North and South Pole switching). While only very slight variations in variations in eccentricity, axial tilt, and precession are known for the true pole. Could the data also be explained by magnetic pole wandering?

    2) “Earth’s electromagnetic field would have been static during the TPW because it is created by the liquid inner core, which would have stayed in place. ” This goes against the currently accepted scientific theory. Measurements of P, S and J waves originating from large earthquakes (Tkalčić & Phạm, 2018) indicate the inner core is solid. The current consensus is that the field originates in the thermal convection of the Outer Core, which might work as suggested. But it all seems improbable.
    3) It is clear that the authors suffer from observational bias: they want something to happen at the end of the Cretaceous (usually taken to be 66 million years ago) because that’s when the meteorite that killed the dinosaurs hit. Wouldn’t that be a spectacular tale: Earth gets knocked on its ass by a meteor.Unfortunately, if the age of these sediment is 84 million years old the wobble came 18 million years too early
    4) What caused the wobble? What caused the Earth to tip back? The energies required are – literally – astronomical. Compare that to the 3-10 TW powering (or reversing) the magnetic field. The latter seems more likely.

    Sagan’s razor: extraordinary claims require extraordinary proof. If this article is a true reflection of what was published in Nature Communications, then their editors are witlings.

    Reply

  • Avatar

    Andy

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    May I ask what a ‘witling’ is?

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    • Avatar

      Koen Vogel

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      Merriam-Webster claims:
      One who has little wit, to wit a pretender to wit; a would-be wit. A witling lacks the ability to think or reason.
      While I’m back I might as well say I read the Nature Com article. Their editors are not witlings, the article above has some misquotes: the Nature Article claims the (fluid) Outer core generates the field. The article still has some significant problems; I added some comments in Nature Communication:
      Central to story is the claim that “As Earth’s magnetic pole is tied primarily to rotationally induced excitations of the outer core, the magnetic poles remain aligned with the rotation axis through a TPW event.” Which is dubious. Uranus has a magnetic dipole tilt (Nasa data) of 58.6; Neptune has a dipole tilt of 46.9. So [their] assumption that “Earth’s magnetic pole is tied primarily to rotationally induced excitations ” requires that the process generating Earth’s magnetic field is unique among the planets. Extraordinary claims require extraordinary proof. A far more likely interpretation of your data is that you have documented a magnetic reversal. Could [their] peak declination in the Santonian indicate an earlier start to C33r or a new reversal ([1]Dinarès-Turell, J., Wolfgring, E., and Wagreich, M., “A new reverse subchron (C33n.1r) in the Campanian: astronomical duration estimate and geomagnetic/chronostratigraphic implications”, 2020.) or age measurement errors?

      If the TPW truly happened then it would have been globally misidentified by all workers as a magnetic reversal (including Dinarès-Turell et al.) so in effect the two are competing models.

      Reply

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