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Thread: Obliquity of the ecliptic

  1. #1 Obliquity of the ecliptic 
    Forum Radioactive Isotope sculptor's Avatar
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    Anyone know the
    Obliquity of the ecliptic / Axial tilt
    circa 1 billion years ago?

    (at the ediacaran/cmbrian boundary-circa 550mybp, it seems to have been 45 degrees, falling toward 25 within 150,000 years)
    this while antarctica was becoming forested?

    Was the earth tilted even more before this 45 degrees, or was it moving within a higher cycle of tilt and precession?


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  3. #2  
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    There is a bit of work on the OP question. This paper suggesting the tilt may have exceeded 54 degrees for much of it's history including during the "snow ball earth" late pre-cambrian period which played a role to reduce it to current levels.

    Low-latitude glaciation and rapid changes in the Earth's obliquity explained by obliquity-oblateness feedback : Abstract : Nature


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  4. #3  
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    thanx for the links
    the first, published 1864 misses the 1975 postulation of a considerable increase in the obliquity of the ecliptic------nice read and really insightful as/re support by modern instrumentation.

    The second was by a different Williams with Kasting and Frakes whose obliquity/oblateness feedback loop as the mechanism for changing the higher obliquity
    I find problematic.
    Lynx: Here is a better link for that whole article: http://www3.geosc.psu.edu/~jfk4/Pers.../Nature_98.pdf

    Here's the original postulation by G.E. Williams (which seems accepted by the Planetary Hability Laboratory---which was The first place in which I read the concept.)

    Summary

    Late Precambrian ( 750±200 Ma) glaciogenic sequences exhibit substantial evidence for marked climatic inequability of seasonal and longer periodicity (10° to 106 yrs): (1) tillites are closely associated with dolomites, limestones and evaporites apparently of warm-water origin; (2) tillites occur with red beds and iron-formations whose iron probably was derived ultimately from lateritic weathering; (3) glacial dropstones occur locally within carbonates and iron-formations; (4) laminae, interpreted as varves by many workers, are common in argillites, carbonates and iron-formations; and (5) permafrost structures attributable to repeated seasonal changes of temperature are locally abundant. Such climatic, particularly seasonal inequability apparently conflicts however with the probable low (30°) palaeolatitudes of deposition of numerous late Precambrian glaciogenic sequences.

    The contradictions presented by such sequences may be resolved by postulating a considerably increased obliquity of the ecliptic (ε) in late Precambrian time. Substantial increase in e would: (1) greatly amplify global seasonality; (2) weaken climatic zonation, thus allowing warm-water sedimentation and lateritic weathering over wide latitudes; and (3) increase the ratio of radiation received annually at either pole to that received at the equator, so when 54° < ε < 126° low and middle latitudes (≤ 43°) would be glaciated in preference to the poles. Ice sheets and permafrost thus can be envisaged principally in low and middle latitudes with contiguous warm-water and iron-rich facies under a markedly seasonal climate. The concept of secular change of e is supported by other geological evidence
    from:
    Cambridge Journals Online - Geological Magazine - Abstract - Late Precambrian glacial climate and the Earth's obliquity

    Still?
    Only a postulation?
    And in contrast with the "snowball earth" hypothesis?

    .
    When first I read of the assumed obliquiyt of > 45 degrees, I wondered, "what would this do to the climate?"
    For instance, would 1/2 year in darkness, and 1/2 year in intense solar radiation in constant daylight balance out to a climate more conducive to the survival of terrestrial plants?
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  5. #4  
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    Quote Originally Posted by sculptor View Post
    Anyone know the
    Obliquity of the ecliptic / Axial tilt
    circa 1 billion years ago?

    (at the ediacaran/cmbrian boundary-circa 550mybp, it seems to have been 45 degrees, falling toward 25 within 150,000 years)
    this while antarctica was becoming forested?

    Was the earth tilted even more before this 45 degrees, or was it moving within a higher cycle of tilt and precession?
    Huh? you seem to be several hundred million years off if you talking about forests in the Antarctic region. Land plants of any type didn't appear until the Ordovician.
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  6. #5  
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    oops I seem to have forgotten a comma and 3 zeroes

    that was supposed to read "falling toward 25 within" 150,000,000 years----
    which would place the end date 90 million years after begin ordovician

    thanks for the heads up
    Last edited by sculptor; June 5th, 2013 at 05:01 PM.
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  7. #6  
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    Ahhhhhhhh, that make much more sense.
    If more of us valued food and cheer and song above hoarded gold, it would be a merrier world. -Thorin Oakenshield

    The needs of the many outweigh the need of the few - Spock of Vulcan & Sentinel Prime of Cybertron ---proof that "the needs" are in the eye of the beholder.
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  8. #7  
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    Not much of a discussion going on here.
    Perhaps we need a different starting point?

    Let us assume that the "normal" axial tilt to be between 21 and 26 degrees, and further that this norm was upset by a bolide contact.

    Could a collision have knocked the earth into a different obliquity of the ecliptic in excess of 54 degrees.

    If so, would it not also alter rotational speed, and orbital path?

    also:
    If so: Then, would interaction with the moon along with earth bound feedbacks be enough to moderate this radical tilt and bring us back to within the normal range of axial tilt?
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