Skip to 2:00 minutes in. Featured Links: Galactic Plane Mass Extinctions: https://arxiv.org/pdf/1610.04239v1.pdf "In the oscillation model, we convolved the predicted tidal force with the comet shower profile of Hut et al. (1987). In the constant rate model, we assumed a constant rate of ND comets per 250 My. We defined the likelihood to be given by the L2 inner product of the predicted rate and the comet history, expressed as a probability density P(t) in time: Likelihood ∝ Z 250 Mya 0 Rate(t) × P(t) dt. (1) The likelihood ratio would therefore be given by the ratio of this quantity computed for the oscillatory model to the quantity computed assuming a constant average rate for the comets. Other effects we account for here are spiral arm crossing and radial oscillations. We assume spiral arms with an amplitude A = 0.1 − 0.3 (Hessman 2015). This corresponds to an arminterarm density ratio of 1.2-1.9 (Binney & Tremaine 2008, Ch.6). As we are currently entering the Orion spur, we assume the current locally measured density to represent the azimuthally averaged density of the disk at the Solar radius. For radial oscillations, we assume a 17% variation in density (Shaviv et al. 2014) with a period of 1.35 Ω0 (Binney & Tremaine 2008, Ch. 3), where Ω0 = Vc/R⊙ is the angular velocity of the circular orbit at the position of the Sun. According to Reid et al. (2014), Vc + V⊙ = 255 ± 5 km s−1 . With a measured tangential velocity of V⊙ = 26 ± 3 km s−1 (Bovy et al. 2012), we therefore estimate Vc = 229 ± 6 km s−1 , with the Gillessen et al. (2009) value of R⊙ = 8.3 kpc. Based on the above value of V⊙, as well as on the Sun’s radial velocity U⊙ = 11 ± 1 km s−1 , we estimate the present phase of the Sun in these oscillations to be 35o . Since there is a lot of uncertainty in the position of the Sun relative to the galactic plane, this will certainly affect whether the model can account for the dinosaur extinction. We therefore compute the likelihood for the value Z⊙ = 26 pc (Majaess et al. 2009) as well as for other values of Z⊙. We also varied the sech2 (z/2hD) scale height hD of the dark disk, as well as the vertical velocity of the Sun W0 (Sch¨onrich et al. 2010) and the dark halo density ρhalo (Bovy & Tremaine 2012). " Clearly....keep on eye on them meteor showers eh? |\/|6
Younger Dryas Comet hit the Ice Age 2 mile thick ice sheet in the Great Lakes Region 12,800 years ago, including some big impacts in Northern Europe, and lots of the smaller debris left the Carolina Craters on the US east Coast. Killed just about everything on North America in just a couple of minutes, maybe even faster, Mammoths, Giant Sloths, extinct type Bison, and the Clovis people. Those frozen mammoths they find with the food still in their mouths were victims of this comet. We know some humans must have survived because the story of the event is in many Native American cultures. The current known boundaries of the debris field reach down into the Andes and over into the Middle East. The Ice Sheet vaporization would have supplied the water for a worldwide flood. We are at that dirty spot in space again, lots of big rocks floating around out there that could devastate our civilization and throw mankind back into the stone age. The paper just emitted by the Harvard scientists essentially says it's a done deal, we're toast at some point. Just goes to show that you can prep all you want to, but if Lady Luck isn't in your corner, you're just another statistic.
