[meteorite-list] Questions [From Chondrule to Planet]

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Fri, 18 May 2007 02:25:03 -0500
Message-ID: <096601c7991d$a78ac7e0$f54de146_at_ATARIENGINE>

Hi, Greg, Mike,

    Chondrules are small, round (more or less)
glassy droplets of molten rock that were "flash
fried" at high temperatures by... something. What
the "something" was, is the cause of long and nasty
arguments among cosmologists. But it was
    a) very hot, and
    b) very quick, and
    c) cooled quickly.

    When this happened to the chondrules, they
were undoubtedly free-floating in low gravity
(because of their generally round shapes) and
not in the presence of any larger bodies. It had
to have happened BEFORE they became part
of anything (like meteorites). This makes them
older than meteorites (they were here first). We
think they are the oldest things in the solar system.

    And sure enough, when you pry them out
of the rock matrix they're embedded in and date
them separately, they ARE older. Just by a handful
of million of years, but older.

    Since they are embedded in meteorites in pretty
much the same way fruit and nuts are embedded
in a fruitcake, this means that the meteorites themselves
were assembled in a relatively quiet fashion, around the
pre-existing chondrules, not hotly enough nor violently
enough to damage the chondrules beyond recognition...
usually.

    Another clue that the meteorites were not violently
assembled is the fact that the rock has varying amounts
of metals just dissolved in the rock, or present as small
droplets. Nobody "forged" meteorites; they just formed
by "hanging out." We assume that almost all the rock
materials had chondrules in them, originally.

    I said "usually" because in some (but not all) meteorites,
chondrules have been damaged, some less, some more, some
to the point where they can hardly be recognized, and in
some meteorites, they have been completely re-melted
and disappeared.

    This general scale of "damage to chondrules" is called
the meteorite's "metamorphic" stage. "Metamorphosis"
means change. If the chondrules are fresh looking, easily
recognized little marbles, all different, and still look like
they did when they formed independently, the history of
that rock has been mild and peaceful (for a rock). The
chondrules haven't changed much, if any. The most
likely peaceful history for a rock is to have been a smallish
rock that never got very hot and was never involved in any
colossal collisions.

    But if a rock gets swept up into a larger body, it's in
for a rough ride, the larger the body, the rougher. Large
bodies have gravity that squishes rock to high pressures;
large bodies have radioactive elements that heat it up to
the point that the rock melts, obliterating the chondrules.

    If all the chondrules have vanished, the meteorite isn't
a chondrite anymore -- it's an achondrite ("a" is greek
for "not"). There is every metamorphic stage from
untouched chondrules to partly re-melted chondrules
to almost melted "ghost" chondrules to no chondrules
at all.

    If the body is even larger, it gets hot enough that the
iron that is mixed freely in the rock melts and drips out to
the center of the body. You end up, in short order, with
a "Tootsie Pop" object -- an iron center, a heavy rock
body, and a light rock candy coating.

    A body big enough for that to happen is called a planet!
(Please, don't anybody start "that" argument.) ALL the rock
and metals, everything that is part of a planet, has been melted,
at least once, and much of it has been melted over and over
again. There may have been countless billions of tons of chondrules
in some or all of the rocks that went into making a planet, but
they (and everything else) get melted. If you could pick the
Earth apart one BB-sized grain at a time, you wouldn't find
a single chondrule!

    The melting and separation of metal and rock is called
"differentiation." The "difference" is that iron sinks and
rock floats. Some meteorites come from differentiated
bodies -- Mars, the Moon, even little Vesta (HED), chips
off the old blocks. Some meteorites, the ones with lots
of crisp fresh chondrules, must be chips from a very
small block that's been hanging around minding its own
business for most of the life of the solar system, waiting
four and a half billion years to accidently run into the Earth,
fall to the ground, be found by some crazy human who will
slice it open and say, "Wow, Look at those chondrules!"


Sterling K. Webb
-------------------------------------------------------------------
----- Original Message -----
From: "mike morgan" <meteoritemike360 at yahoo.com>
To: "greg stanley" <stanleygregr at yahoo.com>;
<meteorite-list at meteoritecentral.com>
Sent: Thursday, May 17, 2007 9:24 PM
Subject: Re: [meteorite-list] Questions


I can answer ? #1. In the book Rocks from Space on
page 181 it says,Chondrules, little spherical
inclusions called chondrules give the chondrite
meteorite its name.The texture is cosmic because
chondrules are not found in terrestrial rocks.

As for ? #2 I am new to all this so I dont really
know. But I know that a lot of people on here will
know for sure.

Mike
--- greg stanley <stanleygregr at yahoo.com> wrote:

> Hello List:
>
> I have two questions:
>
> 1. Has any rock formed on Earth been found
> containing Chondrules in it? If so, what kind of
> rock and where was it found?
> 2. Are there any minerals found in
> Meteorites that are NOT found (or formed) on earth.
>
> Much Thanks,
>
> Greg S.
>
>
>
>
> ---------------------------------
> Need Mail bonding?
> Go to the Yahoo! Mail Q&A for great tips from Yahoo!
> Answers users.>
______________________________________________
> Meteorite-list mailing list
> Meteorite-list at meteoritecentral.com
>
http://six.pairlist.net/mailman/listinfo/meteorite-list
>




____________________________________________________________________________________
8:00? 8:25? 8:40? Find a flick in no time
with the Yahoo! Search movie showtime shortcut.
http://tools.search.yahoo.com/shortcuts/#news
______________________________________________
Meteorite-list mailing list
Meteorite-list at meteoritecentral.com
http://six.pairlist.net/mailman/listinfo/meteorite-list
Received on Fri 18 May 2007 03:25:03 AM PDT