[meteorite-list] The age of Mifflin. ?470 million years? Really?

From: Jeff Grossman <jngrossman_at_meteoritecentral.com>
Date: Fri, 15 Apr 2011 05:41:40 -0400
Message-ID: <003701cbfb51$53495a30$f9dc0e90$_at_com>

It's actually not as silly as everybody seems to think. There are a number
of "ages" that one can speak about for an L chondrite, all of which are
different and all of which are correct. These include a terrestrial age
(how long on Earth), a cosmic-ray exposure age (how long in a small body in
space), shock or metamorphic ages (how long since various heating events),
an accretion age (how long since chondrules, matrix, etc. came together in a
planetesimal), the age of the chondrules, the age of the CAIs, and probably
others. One can also refer to ages based on specific measured isotope
systems, such as an "argon age" (based on the decay of 40K to 40Ar), which
is what the 470 Ma age in this article is. The argon age of L chondrites
dates a major disruption event caused by an impact on the parent asteroid,
resulting in the resetting of the argon isotopic system.

As for the article, it isn't really wrong. If I were to quibble, I'd go the
opposite way. It says "the meteorite dates back about 470 million years."
In point of fact, the meteorite dates back only about 1 year, its
terrestrial age -- before that it was not a meteorite. The meteoroid it
came from probably dates back a few 10s of million years (or whatever the
CRE age might be). The asteroid the meteoroid came from might date back
about 470 Ma, or it might have just been shocked then, depending on the
circumstances. The original L chondrite parent body dates back over 4.5 Ga.


Bottom line: measured ages correspond to events (and sometimes it's not easy
to figure out what that event is, or whether the age has any meaning at
all!). If you just say "age" or "dates back" you are being ambiguous. Is
the age of Mifflin 470 Ma? Yes. And no.

Jeff

> -----Original Message-----
> From: meteorite-list-bounces at meteoritecentral.com [mailto:meteorite-
> list-bounces at meteoritecentral.com] On Behalf Of Sterling K. Webb
> Sent: Friday, April 15, 2011 1:25 AM
> To: Joe Kerchner; meteorite list
> Subject: Re: [meteorite-list] The age of Mifflin. ?470 million years?
> Really?
>
> It's the usual reporter scramble that results
> when a scientist tries to explain something
> more complicated than Brittany Spears or
> Charlie Sheen to a reporter.
>
> Mifflin's an L chondrite. John Valley and
> Noriko Kita have done a lot of work on the fossil
> L chondrites of the Ordovician period, which
> fell at rates 100 times greater than today's fall
> rates, apparently after the breakup of the L
> chondrite parent body sometime shortly before
> 470 million years ago.
>
> They must have tried to explain all this to the
> reporter instead being smart and saying "Yeah,
> it's a rock from outer space and it's really old,
> old as the solar system itself" and just letting
> it go at that.
>
> Sorta like what you would say to a five-year-old.
> Always a good idea to talk to reporters like they
> were five-year-olds. Don't try to make them
> handle too much.
>
> So, all of that got mushed together into this:
> "Scientists believe [it] was originally part of an
> asteroid fragment that separated 470 million
> years ago between Mars and Jupiter." (From
> the other local TV station.)
>
> Remember... Five-year-olds.
>
>
> Sterling K. Webb
> -------------------------------------------------------------------
> ----- Original Message -----
> From: "Joe Kerchner" <skyrockmeteorites at yahoo.com>
> To: "meteorite list" <meteorite-list at meteoritecentral.com>
> Sent: Thursday, April 14, 2011 11:16 PM
> Subject: [meteorite-list] The age of Mifflin. ?470 million years?
> Really?
>
>
> > Hello all,
> > It the 470 million year age for the Mifflin meteorite correct? if
> > so, isn't that very young for a meteorite? I have been under the
> > impression that the average age of a meteorite was 4.57 Billion years
> > old I know that's an average, but isn't 470 million way too young?
> > Theres no way that it is so young, is there?
> > I read that in a couple articles online today. below is a link to one
> > of them.
> > http://www.wisn.com/r/27539805/detail.html?source=htv
> >
> >
> > Best Wishes,
> > Joe Kerchner
> > http://illinoismeteorites.com
> >
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Received on Fri 15 Apr 2011 05:41:40 AM PDT