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    Default Explanation of Lunar Mare (??)



    In the Lunar geologic [Lono-logic??] timescale, the "Early Imbrian Epoch" (3850 - 3800 million years ago*) is associated with the Late Heavy Bombardment, and the resulting huge impact basins, which would later fill w/ lava to form the Lunar Mare, during the ensuing Late Imbrian Epoch (3800 - 3200 million years ago). This happened when "the mantle below the lunar basins partially melted and filled them with basalt"**.
    Now, it is well-known that the Moon first formed roughly 15 times closer to Earth than its present orbit today*. And, that early Moon was not, yet, Tide-Locked to the Earth. But, by the present period, not only is the Moon Tide-locked to the Earth, but it's whole inner iron Core has shifted Earthwards inside the Moon, thinning the Crust & Mantle on the Near Side, while thickening the same on the Far Side**.
    * National Geographic Channel Naked Science — Moon Mysteries (TV)
    ** Carroll & Ostlie. Introduction to Modern Astrophysics [1st ed.], pp. 800-801.


    "Only one Mare was seen on the side of the Moon furthest from the Earth. This is not b/c collisions were preferentially occurring on just one side; rather, the Crust is actually thinner on the Near Side. Consequently, impacts on the thin-crust side were more likely to penetrate the Crust, allowing interior molten rock to flow over the surface. B/c the Crust is less dense than material in the Moon's interior, tidal forces have caused the heavier Near Side to permanently 'hang down' toward Earth" (Carroll & Ostlie, ibid.).

    CONCLUSION: We must explain why, during the Late Imbrian Epoch (3800 - 3200 million years ago), impact basins on the Moon's Near Side flooded with lava, when the Mantle beneath them suddenly heated & melted. But, we have seen, that once the Moon became Tide-locked to the Earth, its whole inner iron Core migrated towards the Earth — and the Near Side surface. And, moving all that hot material towards the Near Side surface could easily explain the melting of the overlying Mantle, and subsequent flooding of the Mare.

    This strongly suggests, that by about 3800 million years ago, the Moon had become Tide-locked to the Earth — even as deep basins had been punched into the Lunar surface from the Late Heavy Bombardment. And, over the next 600 million years, the Moon's inner iron Core migrated ever Earth-wards, continually melting the ever-thinning over-lying Mantle on the Near Side, which then flooded the Near Side surface basins with basalts, making the Mare.

    Indeed, in essence, once the Moon became Tide-locked to the Earth, the Moon's molten inner Core almost melted its way through the Moon, towards the Earth (!!). Had the Moon been bigger, and hence hotter for longer, perhaps the Moon's molten Core could have melted out of the Moon, and fallen back down towards the Earth (!!).
    Last edited by Widdekind; 12-16-2009 at 12:30 PM.

  2. #2
    Widdekind's Avatar
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    Default

    http://jbartin.com/SPS/unit%203/the%...(post-lab).ppt.

    Mare (pl: maria)
    Latin for seas
    Large, solidified pools of ancient basaltic lava
    Much more common on near side of moon
    + 31% of near side surface
    + 2% of far side surface

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    At the present epoch, the Moon's orbit is:
    • ~400,000 km from the Earth
    • receding from the Earth at the rate of ~4 cm / year

    Thus, at its present speed of spinning out & away, it would have taken the moon ~10 Gyr to reach its current orbit. But, we know that Moon has made it out to its present position in less than half that time (~4.5 Gyr).

    This strongly suggests, that, in the distant past, the early Moon was spinning out & away from the Earth much more rapidly than presently. Indeed, Tidal Forces scale in inverse proportion to the cube of the orbital distance. So, when the Moon was 10x closer, it experienced (and induced) Tidal Forces 1000x as great. Indeed, when the Moon first formed, roughly 15x closer than today, it's Tidal Forces were over 3300x as great, and created ~10 km ocean tidal waves (which ripped across any early continents), and Rock Tides perhaps 1 km tall (!!).

    Furthermore, from the Moon's geological [Luno-logical ??] record, we see that there was some sort of time of transition, about 3800 million years ago, when the Moon became completely Tide-Locked to the Earth. (So, it's been nearly 4 Gyr since Earth last saw the far face of its satellite.)

    CONCLUSION:

    Linearly retro-dicting the Moon's current recession rate back about 3800 million years (~4 Gyr) can account for nearly half of its total recessional travel (ie., nearly half of its current orbital radius).

    Thus, "in round numbers", from ~4.5 to 3.8 Gya, the Moon's orbit was dramatically impacted by Tidal-Forces. During those ~700 Myr, the Moon:
    • Orbited out to about half of its present orbital radius (~200,000 km)
    • "Spun down" and became completely Tide-Locked to the Earth

    And, since that time, over the past ~3.8 Gyr, the Moon has been much more quiescent, essentially "coasting" ever further outwards, to its present position, by the present period
    .

    However, the Imbrian Epoch (3.8 - 3.2 Gya) was the time of transition, between these two periods, first of dramatic Tidal interactions (before 3.8 Gya), and later of quiescent "coasting" ever further outwards (after 3.2 Gya). During this transitional time, the Moon's still-molten inner iron Core gravitated towards the Earth, melting its way through the Moon's interior, and melting the Mantle on the Near Side, to push "bleeding" basaltic lava flows out into the Near Side's deep impact basins, making the Maria.

 

 

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