Now lets not get crazy here.<br /><br />Point 1: comets have never been peripheral objects.<br />In the past they were highly weighted omens. History was altered by their appearence. I hardly consider that peripheral. They shaped history!!<br /><br />Point 2: AFAIK, no definitive classification has been made of the Chixalub impactor, but so far an asteroid is more likely.<br /><br />Yes comets have some potential to wipe out life on earth. Beacuse the energy is squared for the impact velocity, and most asteroid impacts are near 25 km/s, while comets can reach 73 km/sec, a smaller comet can wreak the same damage as a much less massive asteroid.<br />That's all a crapshoot. And because an Oort cloud comet comes sceaming in,<br />we may only have months to react, rather than the decades fo a known asteroid.<br /><br />Earth's water may have had multiple souces, i.e. volcanism, comets, and even an unknown source. All the evidence is not in yet.<br /><br />What the heck does Pluto have to do with this????????<br />You must explain that! <div class="Discussion_UserSignature"> <p><font color="#000080"><em><font color="#000000">But the Krell forgot one thing John. Monsters. Monsters from the Id.</font></em> </font></p><p><font color="#000080">I really, really, really, really miss the "first unread post" function</font><font color="#000080"> </font></p> </div>