[Rockhounds] Astronomers: A comet fragment, not an asteroid, killed off the dinosaurs

[pmodreski]

That's an interesting story, Kreigh, thanks for sharing!I must admit, first reading the short summary, it sounded awfully speculative (how do they know all that--just guessing?). But reading the arstechnica story about it by Jennifer Oullette, well, it explains pretty well the logical reasoning behind it.Kreigh, I do have one question about the background facts relating to Chicxulub and this hypothesis, which I just don't know, so perhaps you do. How/why do they believe that the Chicxulub impactor was a carbonaceous chondrite? I haven't been following all the literature on this, and I just don't know the answer to that--what data that is based on. Some quick browsing on Google/Wikipedia doesn't lead to any explanation of why that is believed to be so.Thanks!PeteSent from my Verizon, Samsung Galaxy smartphone
-------- Original message --------From: Kreigh Tomaszewski <kreigh at gmail.com> Date: 2/15/21  6:50 PM  (GMT-07:00) To: "Rockhounds at drizzle.com: A mailing list for rock and gem collectors" <rockhounds at rockhounds.drizzle.com> Subject: [Rockhounds] Astronomers: A comet fragment, not an asteroid,
  killed off the dinosaurs Jupiter's gravity pushed comet toward Sun; comet was ripped apart by tidalforces.Some 66 million years ago, a catastrophic event occurred that wiped outthree-quarters of all plant and animal species on Earth, most notablytaking down the dinosaurs. An errant asteroid from the asteroid belt<https://en.wikipedia.org/wiki/Asteroid_belt> has been deemed the mostlikely culprit. However, in a new paper<https://www.nature.com/articles/s41598-021-82320-2> published inScientific Reports, Harvard astronomers offer an alternative: a specialkind of comet—originating from a field of debris at the edge of our solarsystem known as the Oort cloud<http://their%20findings%20also%20offer%20evidence%20that%20the%20unusual%20composition%20of%20the%20chicxulub%20impactor%E2%80%94carbonaceous%20chondrite%E2%80%94indicates%20it%20originated%20from%20the%20oort%20cloud%2C%20and%20not%20from%20the%20main%20asteroid%20belt%2C%20as%20suggested%20by%20one%20of%20the%20more%20popular%20origin%20theories.%20it%27s%20a%20rare%20composition%20for%20main-belt%20asteroids%2C%20but%20common%20among%20long-period%20comets.%20the%20authors%20also%20point%20to%20other%20impact%20craters%20with%20similar%20composition%2C%20most%20notably%20the%20vredefort%20crater%20in%20south%20africa%E2%80%94the%20result%20of%20an%20impact%20some%202%20billion%20years%20ago%E2%80%94and%20the%20zhamanshin%20crater%20in%20kazakstan%2C%20from%20an%20impact%20within%20the%20last%20million%20years.%20those%20times%20frames%20are%20in%20line%20with%20siraj%20and%20loeb%27s%20calculations%2C%20which%20indicate%20such%20objects%20should%20strike%20earth%20once%20every%20250%2C000%20to%20730%2C000%20years./>—thatwas thrown off course by Jupiter's gravity toward the Sun. The Sun'spowerful tidal forces then ripped pieces off the comet, and one of thelarger fragments of this "cometary shrapnel" eventually collided with Earth.https://arstechnica.com/science/2021/02/astronomers-a-comet-fragment-not-an-asteroid-killed-off-the-dinosaurs/_______________________________________________Rockhounds mailing listSubscription Services:  http://rockhounds.drizzle.com/mailman/listinfo/rockhounds_rockhounds.drizzle.comList Usage Policy: http://Tomaszewski.net/Kreigh/Rockhounds/Rockhounds.shtml