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    Default Spiral Arms, Supernovae, & Mass Extinctions



    Prof. Richard A. Muller has shown that the Lunar cratering rate actually increased, beginning about 400 Mya*:
    By extension, the cratering rates on the Earth, and even across the Inner Solar System, likely increased too, from ~400 Mya.
    * PBS Exploring Space — The Quest for Life (DVD)
    A.J. Meadows (The Future of the Universe, pp. 118-125) says that, as our Sun orbits around the Galaxy, it travels into, thru, and out of, our Galaxy's Spiral Arms; and, that these can cause close encounters with Star Forming Regions, on ~200-500 Myr time scales:
    The Sun is currently positioned near the edge of a Spiral Arm... The local arm, and the Sun, are moving at different speeds, so that Sun is not a permanent member of the arm... So, the Sun is sometimes embedded in a Spiral Arm, and sometimes not. Encounters between the Sun, and a Spiral Arm, occur every few hundred million years... How near the Sun ventures to newly forming stars [in Interstellar Clouds, in Spiral Arms] will vary from from one passage through a Spiral Arm to the next. Big Interstellar Clouds, where new stars preferentially form, are often fairly isolated from each other. The spaces between them are usually several times the size of the individual clouds. Consequently, the Sun may only encounter a big cloud in every 5-10 spiral-arm passages, so it is difficult to guess what any individual passage will bring, in terms of Cosmic Rays (CRs) [from young stars, formed from Interstellar Clouds]. Still, looking to the future, we can predict, that the Earth will face increased exposure to CRs every few hundred million years or so — in reasonable agreement w/ the past frequency measured from meteorites. But, we can add that, once or twice in the next billion years, the Solar System can expect to receive a really massive dose of CRs.
    And, in addition, the Ordovician Mass Extinction Event (~450 Mya) could, conceivably, have been caused by a powerful Supernova explosion occurring near our Solar System*.
    * Wikipedia; History Channel Mega Disasters — Gamma Ray Burst (TV); Animal Planet Animal Armageddon — Death Rays (DVD)).
    Finally, the KT Mass Extinction Event (~65 Mya) was probably caused by an asteroid born from the Baptistina Family, the rubbled remains of a massive body which was broken apart about 160 Mya (and likely caused the crater Tycho on the Moon, about 110 Mya, as well)*. This shows that gravitational disturbances can take ~50 Myr to propagate down into the Inner Solar System, and that they can last for as long as ~100 Myr.
    * Wikipedia; History Channel Jurassic Fight Club — Armageddon (DVD); National Geographic Naked Science — Dino Meteor [??] (TV)
    All this seemingly suggests a scenario, wherein, during a transit across a Spiral Arm, our Sun closely encountered a Star Forming Region & Supernova ~450 Mya. Radiation from the Supernova immediately caused the Ordovician Mass Extinction, but was also associated with a gravitational disturbance of the Oort Cloud — which, after a further ~50 Myr, caused increased cratering rates across the Inner Solar System (called a "Comet Swarm"). Perhaps there is even some kind of connection to the vigorous resurfacing events on Venus over the last 300-500 Myr.
    Last edited by Widdekind; 12-17-2009 at 05:31 AM.

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    With my limited knowledge, I find it extremely plausible. I've never even considered any of this, thank you very much for introducing such interesting ideas.

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    You gotta think, even the biggest telescopes we have cannot see the little things far away from the sun.
    It's very possible that the solar system can go through clouds of debris, from old stars, failed systems, there is much more stuff out there than just stars and DSO's.
    I mean just looking into the centre of the milky way there is much dust.

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    Thanks for the thanks again !

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    If gravity waves exist, I wonder if the distance between arms is indicative of the wavelength of those hypothetical waves.

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    There is no proven conx betwn gravity waves (as gw theoretically postulated) and galactic structure - that is pure conjecture. Most prolific galaxy shape is the elliptical.

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    Interesting new info for me. I've not encountered that concept before. Thanks.

 

 

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