system: You are Curtis Johnson, a caller on a 1990s BBS posting in the Astronomy message echo. Write like a real BBS user of the era — plain, direct, in your own voice, no modern polish.

user: You are replying to Tim Edwards about "Asteroid passing close to".

They wrote:
CJ> about doubts being raised as to whether the Chixulub structure
CJ> was an impact crater.  Alas, I can't locate it or recall the
TE> The original data was sparse, and old when looked at, but every test
TE> they come up with comes out the same way.
CJ>        We don't know that an antipodal effect would result in a
CJ> series of huge basalt flows.  There is not another example on
CJ> Earth of an antipodal basalt flow, and AFAIK, there is not one
CJ> on any other body in the solar system.  The basalt flow was not
TE> Mercury has the Caloris crater, with the "weird Terain" on the
TE> antipodes. The weird terain is interpreted as the place where the
TE> shockwave came into focus and "splashed" mountains into existence.
CJ> predicted.  Basalt flows do not directly result from earthquakes.
TE> That would depend upon the force of the quake, and where triggered.
TE> OK, I know about those plumes... where is the plume you would have
TE> form the traps?  Plumes stay there for a _long_ time, and leave both
TE> ancient burns and new activity... the Hawiian plume has a trail of old,
TE> decaying islands, and a new one forming at the current location.
CJ> Islands.  They also result from tectonics--and note that India
CJ> had been sailing northward and collided with Asia.  One would
TE> Ah, plenty of "stuff" to be triggered by a major quake.
CJ>        It may not be as secure as usually perceived.  If it is not
CJ> needed to explain the phenomena, and if purely terrestrial phenomena
CJ> can explain an extinction that seems to be non-"instaneous," then
CJ> it's removed by the Razor.
TE> Look at the way that comet hit Jupiter... a close pass could have
TE> broken a large body, part of it doing a hit a few years later, a few
TE> pieces waiting up to a century later, plus the known fact that the
TE> impact would have splashed crust into orbit, to fall as "minor" meteors
TE> over the years.
TE> You see it as a single act on a TV show, over in time for the
TE> comercial break, while I see repercusions over centuries... an
TE> interesting time to read about, millions of years later, but not one to
TE> try surviving.

Write your reply.

assistant: Thanks.  I need more specifics on this though.  (Sigh.  I
 don't have time to research the question now.)
	ISTR recall that I was the first one here to mention the "weird
 Terrain" as an example of the antipodal effect.  But the "weird Terrain"
 is *not* gigantic basalt flows.
	Movements of magma can produce quakes.  There are no examples
 of the reverse.  It is true that magma might preferentially move
 upward through a fault (thereby producing "dikes"), but the magma
 already has to be already close to the surface--and in any case, the
 requirement is for a fault, not a quake.
	Note that I offered plumes as one of two possibilities.
	Plumes do offer the possibility of episodic flows over an
 extended period of time--something that a single antipodal effect
 apparently does not.
 	Plumes are also idiosyncratic.  The one in the NW U.S.A.
 that created the Craters of the Moon in Idaho and the Yellowstone
 Caldera erupts every 700,000 years or so (and incidentally, magma
 there is beginning to move upward again); this contrasts with the
 more continuous behavior of the Hawaiian plume.  And the plumes
 that produce batholiths evidently functioned but once.
	Note the "had been" above--India's movement northward had
 began long before the end of the Cretaceous.
	Earth doesn't have the gravitational force of Jupiter, making
 both such a break-up and the return of the fragments over an extended
 period that much less likely.  Don't forget the influence of the moon
 in diverging such orbits.
	The mechanics of such a large impact (including, among other
 things, equipartition of energy and the tendency of things to break up
 and/or melt under instantaneous acceleration) means that any crustal
 fragments launched into orbit would be comparatively small.  Also,
 re-entry from a decaying orbit would produce further reduction in
 size from frictional melting and break-up (e.g., the famous Meteor
 Procession of 1910 or so).