Obliquity Not Stable – Massive Historic Climate Change

We all know Obliquity (tilt) wanders in a nice little range from about 22 degrees to 24.5 right?

Well, seems it’s not all that stable if you look further back in time.

https://en.wikipedia.org/wiki/Axial_tilt

In astronomy, axial tilt, also known as obliquity, is the angle between an object’s rotational axis and its orbital axis, or, equivalently, the angle between its equatorial plane and orbital plane. It differs from orbital inclination.

At an obliquity of zero, the two axes point in the same direction; i.e., the rotational axis is perpendicular to the orbital plane. Earth’s obliquity oscillates between 22.1 and 24.5 degrees on a 41,000-year cycle; the earth’s mean obliquity is currently 23°26′12.9″ (or 23.43693°) and decreasing.

Over the course of an orbit, the obliquity usually does not change considerably, and the orientation of the axis remains the same relative to the background stars. This causes one pole to be directed more toward the Sun on one side of the orbit, and the other pole on the other side—the cause of the seasons on the Earth.

But it wasn’t always like that…

https://www.sciencedirect.com/science/article/pii/001282529390004Q

History of the earth’s obliquity
George E.Williams

Abstract

The evolution of the obliquity of the ecliptic (ε), the Earth’s axial tilt of 23.5°, may have greatly influenced the Earth’s dynamical, climatic and biotic development. For ε > 54°, climatic zonation and zonal surface winds would be reversed, low to equatorial latitudes would be glaciated in preference to high latitudes, and the global seasonal cycle would be greatly amplified. Phanerozoic palaeoclimates were essentially uniformitarian in regard to obliquity, with normal climatic zonation and zonal surface winds, circum-polar glaciation and little seasonal change in low latitudes. Milankovitch-band periodicity in early Palaeozoic evaporites implies ≈ 26.4 ± 2.1°at ∼ 430 Ma, suggesting that the obliquity during most of Phanerozoic time was comparable to the present value. By contrast, the paradoxical Late Proterozoic (∼ 800−600Ma) glacial environment— frigid, strongly seasonal climates, with permafrost and grounded ice-sheets near sea level preferentially in low to equatorial palaeolatitudes—implies glaciation with ε > 54° (assuming a geocentric axial dipolar magnetic field). Palaeotidal data accord with a large obliquity in Late Proterozoic time. Indeed, Proterozoic palaeoclimates in general appear non-uniformitarian with respect to climatic zonation, consistent with ε > 54°.

So it was a couple of degrees more than present max at 26.4 degrees around 439 million years ago, and prior to about 700 million years ago it was in flopped over nearly chaotic range. Golly.

It is postulated here that the primordial Earth acquired an obliquity of ∼ 70° (54° < ε < 90°) from the Moon-producing single giant impact at ∼ 4500Ma (approach velocity ≈ 5–20km/s, impactor/Earth mass-ratio ≈ 0.08−0.14). Secular decrease in ε¯subsequently occurred under the dominant influence of dissipative core-mantle torques. From 4500-650 Ma, ε¯slowly decreased to ≈ 60° (〈ε⋅〉=−0.0009"/cy), ε¯then decreased relatively rapidly from ∼ 60° to ∼ 26° between 650 and 430 Ma ((〈ε⋅〉=−0.0556"/cy)); climatic zonation changed from reverse to normal when ε¯∼ 610 Ma, and 〈ε˙〉and the rate of amelioration of global seasonality were maxima for ε¯= 45°at∼ 550Ma (the precessional rate Ω is maximum when ε= 45°, and ε⋅pvaries as Ω^2 ). Since 430 Ma, 〈ε˙〉has been ≲ −0.0025″/cy and ε¯has remained near its Quaternary range.

The postulated relatively rapid decrease in ε¯between 650 and 430 Ma may partly reflect special conditions at the CMB which caused significant increase in dissipative core-mantle torques at that time. This inflection in the curve of ε¯versus time centred at = ε¯45°also may be partly explained by the function ε⋅p∞ (Ω^2 /ω)(sin2ε), where ω is the Earth's rate of rotation, and other dynamical effects on ε⋅p.

[…]
The Proterozoic-Phanerozoic transition may record profound change in global state caused by reduction in ε¯through the critical values of 54° and 45°. The postulated flip-over of climatic zonation at ∼ 610 Ma (ε¯= 54°) coincides with the widespread appearance of the Ediacaran metazoans at ∼ 620−590Ma, and the interval of most rapid reduction of obliquity and seasonality at ∼ 550Ma (ε¯= 45°) with the “Cambrian explosion” of biota at 550 ± 20Ma.
These two most spectacular radiations in the history of life thus may mark the passage from an inhospitable global state of reverse climatic zonation and extreme seasonality (the Earth’s Precambrian “Uranian” obliquity state) to a relatively benign state of normal climatic zonation and moderate seasonality.

Further geological, palaeomagnetic and geochronological studies of Precambrian glaciogenic and aeolian deposits can test the predictions of a large obliquity (ε > 54°) and reverse climatic zonation and zonal surface winds during the pre-Ediacaran Precambrian.

Well, doesn’t that make CO2 look like a piker…

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About E.M.Smith

A technical managerial sort interested in things from Stonehenge to computer science. My present "hot buttons' are the mythology of Climate Change and ancient metrology; but things change...
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13 Responses to Obliquity Not Stable – Massive Historic Climate Change

  1. Coal was mined on Spitzbergen Island inside the Arctic circle until a few years ago. There is still plenty of coal there. Drilling has also located coal on the Antarctic mainland. The climate at the poles must have been different in the past. This is evidence for a change in the tilt. There is also evidence of the magnetic poles reversing

  2. Larry Ledwick says:

    Those items may also be totally or partially explained by continental drift.
    Also I am not sure they have adequately discussed their assumption about the magnetic field structure and the rotational axis of the earth.

    (assuming a geocentric axial dipolar magnetic field)

    There is considerable reason to suspect that there is more than one configuration of a magnetic pole arrangement around a rotating planet. It might have other structures than a pure simple dipole. We also do not know how closely constrained the magnetic poles are to the axis of rotation. We know that the current magnetic poles wander (and have been on a rather dramatic shift in recent years.) When was in boy scouts as a teen the magnetic declination in Colorado was about 14.5 degrees east of true north, some 55 years later it is just about 8-10 degrees and decreasing.

    https://www.nasa.gov/vision/earth/lookingatearth/29dec_magneticfield.html

    https://www.ngdc.noaa.gov/geomag/GeomagneticPoles.shtml

    The most recent survey determined that the Pole is moving approximately north-northwest at 55 km per year. That is slightly more than a kilometer a week.

    https://maps.ngdc.noaa.gov/viewers/historical_declination/

  3. Graeme No.3 says:

    Too late in the night but I thought there was evidence of a change in ancient Egypt from the alignments of temples, over 2200 BC. Will follow up.

  4. u.k.(us) says:

    Not sure this even fits, but when you watch a top spin down, it goes through some gyrations where it almost “spins out” and then stands right up again.

  5. E.M.Smith says:

    @Graeme No3:

    As I recall it, the Egyptian temples were aligned to the sky in keeping with known current precession. They are too young to show deep time changes (million year stuff); however, some only made sense if 10,000 yrs old and that is used to postulate an earlier history timeline.

    @u.k.(us):

    I think that is related to the point catching on irregularities in the surface. The Earth analogy is lunar tugging on the equatorial bulge and the potential fora “electric universe” homopolar motor effect from cosmic currents.

    FWIW, as the moon gets further from us obliquity is supposed to become less stable due to the tug on the tidal bulge diminishing.

    The other missing bit is just what happens to obliquity when big meteors hit? Like the dinosaur killer. I know we’ll all be smoked by the impact anyway, but: Does the Earth take a big wobble then stabilize again? At the same center of rotation? Think whacking a resilient volleyball in flight. I’d guess “it’s gonna leave a mark” and some rotation artifact. Maybe. When big.

  6. u.k.(us) says:

    Now imagine a “top” spinning in the near vacuum of space, apparently in free fall around the sun, and start shooting things (asteroids) at it.
    There is “no” gravity in free fall, what would it take to upset the “top”?, and just what part of its gyrations are we even witnessing during our limited study of it.
    Magnetic lines left in the rocks in the spreading centers of the Atlantic Ocean indicate an 180 degree shift in polarity every ~ 100,000 years.
    Does the “top” go upside down ??

  7. ossqss says:

    What about the unseen molten center of the planet impacting things? We have a wandering/wobbling magnetic North pole already. I remembered this old article. Not sure if things have changed since then.

    https://news.nationalgeographic.com/news/2009/12/091224-north-pole-magnetic-russia-earth-core.html

  8. J Martin says:

    I like the binary star theory that says that precession delivered via the earth’s axis doesn’t exist and that it’s due to our solar system orbiting another star.

    http://binaryresearchinstitute.com/bri/introduction/precession-of-the-equinox/

    This makes obliquity key in insolation, it always annoys me when people include precession as part of insolation curves as they are leading themselves down the garden path introducing a factor in their calculation of insolation that in fact should not be included.

  9. u.k.(us) says:

    Almost forgot, lets throw some magnetism into the mix :)

  10. E.M.Smith says:

    @u.k.(us):

    Oh yeah… it was magnets what done it! (only 1/2 ;-) as there are major mag fields involved with the electrical flows…

    @J. Martin:

    There’s a significant problem with precession that is cured by the partner dark star theory. IIRC it is that there ought to be a change relative to the other planets and there is none… We’re all precessing as a group, ergo not the Earth doing it…

    @ossqss:

    AND the polar alignment of the core doesn’t always match that of the mantel / crust…

  11. E.M.Smith says:

    Ah, here’s the bit I was remembering:

    http://binaryresearchinstitute.com/bri/evidence/the-lunar-cycle/

    Ironically, astronomers unknowingly recognize the two different frames at work when it comes to routine calculations within the solar system. For example, when they plot the position of planets or moons within the solar system they use a tropical frame, which by definition excludes precession (Footnote 2) thus no precession adjustment is required or even considered. However, when the position of a star needs to be found you first find the object at a point in time (say J2000) then add precession for each year that has passed since that point. Thus current ephemeris methods account for the two frames; precession is excluded when plotting objects within the solar system and included when plotting objects outside the solar system.

  12. P1gsn0rtnnm says:

    It would be an interesting test to take a top that looks like a globe of the earth get is spinning and then shoot it with an air soft gun and see who it reacts to an impact by a body of much smaller mass.

    Maybe do a video of it

    To get the right mass scaling you would probably need to use a 15# bowling ball for the globe though.

  13. E.M.Smith says:

    @P1gsn0…

    Well, that would depend on the impactor you were modeling…

    I think the harder bit might be getting it moving at 50,000 miles per hour…

    And remember energy goes as mV^2 so that V has to be right…

    At one time the Moon (well, really, the precursor to it) was an impactor. Sent at least 1/6 of the planet combined masses into space again to become the moon, and who knows how much off to other orbits or rained back down onto the proto Earth.

    Now the physics of things tends to eventually flatten all the orbits into one plane and one surviving angular momentum vector. BUT it can take a few million (or billion) years…

    Thinking about the model question… It would likely work better with much lower masses (so more like a basket ball) as the V^2 is going to be way low. Not seeing an easy way past that. Best would just be to do it in a physically accurate computer simulation. You can avoid the whole problem of momentum going as MV and energy as MV^2 getting screwed up by model sizes.

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