[meteorite-list] Venus, Earth and Widmanstatten lines

From: Rob McCafferty <rob_mccafferty_at_meteoritecentral.com>
Date: Mon, 7 Sep 2009 18:18:29 -0700 (PDT)
Message-ID: <578001.3783.qm_at_web55208.mail.re4.yahoo.com>

It seems likely that Venus may well still be volcanic though this is by no means certain and it is unlikely that we will witness volcanic eruptions in the near future due to the clouds.

Current theory suggests that the hot crust due to the overly hot and thick atmosphere is much more plastic than Earth's and without plate tectonics (which really seem to need liquid water on the surface for some reason) the heat builds up until the whole crust seems to catastophically overturn.
Whether this process will continue in the future is the main question. Venus is approx 80% mass of the earth. We simply do no know.

Earth will certainly cool over time.
The core is solid, not liquid, as I have seen posted. We know this from seismographs. The outer core is liquid and is believed (though we do not know how) to be responsible for the magnetic field. The hotter core is kept solid by the pressure of the overlying material.
Plate Tectonism is predicted to die away over the many aeons ahead. I think there is some prediction to the stop date. It's before the sun expires but not before humanity, methinks. I forget. 1-2Ga or so, I think, but please don't quote me on that.


Widmanstatten lines are uniquely cooling features. Pressure features are not the same. I assume people are thinking about the patterns shown in samuri swords. They are indeed very pretty but not formed the same way. The patterns are due to variations in nickel concentration. The boundaries have more nickel (Taenite in the boundaries vs Kamacite in the thicker parts)

How thick the pattern is depends on the cooling rate. This is because even in a solid, atoms can diffuse. The do so quicker at higher temperature than lower and the boundaries form as the nicke moves out of the structure of the iron. The quicker this happens, the less opportunity it has to do this and so the widmanstatten pattern is thin.
Long slow diffusiuon rates produce thick widmanstatten patterns.

Remember, we are talking about atoms moving in a solid. This is a really slow process.

But widmanstatten is definitely a temperature and time driven effect rather than a pressure one. The physics and geochemistry is well understood.

Rob McC



--- On Sun, 9/6/09, Sterling K. Webb <sterling_k_webb at sbcglobal.net> wrote:

> From: Sterling K. Webb <sterling_k_webb at sbcglobal.net>
> Subject: Re: [meteorite-list] Slow cooling rate of irons in space
> To: "Rob McCafferty" <rob_mccafferty at yahoo.com>, meteorite-list at meteoritecentral.com
> Date: Sunday, September 6, 2009, 5:21 AM
> Hi,
>
> > Venus they're not sure about.
>
> One thing I think we can be sure about is that
> no one will ever use the phrase "so darn cold"
> about Venus, as we stand next to a small creek
> running with liquid lead and other low melting
> point metals...
>
> There are signs that may be recent activity on
> Venus in some areas, but interpreting them
> is in dispute. Generally, the surface of Venus
> appears to have formed all at one time, crater
> dated at 480 +/- 80 million years ago. The lack
> of long-term change is attributed to the fact
> that Venus's crust is, compared to the Earth's,
> extremely thick and rigid, with no detectible
> tectonic movement, recent mountain building,
> or any of the other features of a "terrestrial"
> planet. But, given the similarity in size, density
> (and hence composition) to the Earth, few doubt
> that Venus' core is as hot and active as our own.
> It's just that nothing? (much) can punch its way
> through that heavy crust.
>
>
> Sterling K. Webb
> ----------------------------------------------------------------
> ----- Original Message ----- From: "Rob McCafferty" <rob_mccafferty at yahoo.com>
> To: <meteorite-list at meteoritecentral.com>
> Sent: Saturday, September 05, 2009 7:00 PM
> Subject: Re: [meteorite-list] Slow cooling rate of irons in
> space
>
>
> The "so darn cold" thing refers to objects not being
> lit/heated by their star. Day sides will heat up until they
> radiate more heat than they absorb. Night sides will cool as
> quickly as physics (and any atmosphere) allows.
> If one face of Mars stayed pointing at the sun all the
> time, it would be quite warm on a permanently daylit side.
> It attains 20degC at the equator during the day as it is.
>
> Given that the only method of heat transfer is conduction,
> requiring direct contact of atoms, until you get to the
> surface where they can radiate heat away, it seems more
> reasonable that a moderately sized body may keep a hot core
> warm for a very long period of time. Particularly if you
> have the core covered with a crust made of poorly adjoined
> fragements of rock, acting as a blanket possibly hundreds of
> km deep.
>
> The physics of the planetary cooling has long been worked
> out. For me, the amazing thing is just how the mass of the
> planet changes the cooling time.
> Mars is believed to have stayed hot enough to keep it's
> volcanoes going until 1Ga ago. Now it's interior is too
> cold.
> Smaller bodies generally stopped being active much earlier.
> Venus they're not sure about.
>
> Rob Mc
> Rob McC
>
>
> --- On Sun, 9/6/09, Pete Shugar <pshugar at clearwire.net>
> wrote:
>
> > From: Pete Shugar <pshugar at clearwire.net>
> > Subject: Re: [meteorite-list] Slow cooling rate of
> irons in space
> > To: "Carl 's" <carloselguapo1 at hotmail.com>,
> meteorite-list at meteoritecentral.com
> > Date: Sunday, September 6, 2009, 12:34 AM
> > May I please inject just the one
> > comment?
> > In space, the side facing the star (in our case, the
> sun)
> > can get quite hot, ie close to the sun --hotter, and
> further
> > away---less hot.
> > Conversly--the side away from the star can approach
> very
> > high negative degrees, ie 250 to 400 below zero.
> > This is the "so darn cold" you were thinking about.
> > Pete
> >
> > ----- Original Message ----- From: "Carl 's" <carloselguapo1 at hotmail.com>
> > To: <meteorite-list at meteoritecentral.com>
> > Sent: Friday, September 04, 2009 8:18 PM
> > Subject: [meteorite-list] Slow cooling rate of irons
> in
> > space
> >
> >
> >
> >
> > Hi Elton and All,
> >
> > I've read about the very slow cooling rate of the
> molten
> > iron in various books but I don't understand why this
> is so.
> > Why would it take millions of years for just a few
> drops of
> > degrees? It's hard for me to envision this even
> accounting
> > for bombardments and radioactive decay. Radioactivity
> from
> > the original super nova event, right? Maybe it's
> > because I think of space as being so darned cold it
> wouldn't
> > take anything long to lose heat and freeze up. I
> realize
> > radioactivity takes a long time to decay but would it
> take a
> > lot or so little to keep a large planetary body hot
> for so
> > long? Thanks.
> >
> > Carl
> >
> >
> >
> > Eman wrote:
> > > I think this theory has a potential fatal flaw if
> what
> > we think we know about
> > taenite/kamacite growth is valid. Without an
> insulating
> > blanket the molten
> > pool will not exist in a molten state long enough to
> permit
> > crystallization aka
> > Widmanstatten patterns.
> >
> > Be it remembered that Widmanstatten pattern/crystal
> growth
> > is very very slow on
> > the order of 10's of degrees cooling per million
> years. It
> > is difficult to
> > develop a scenario that integrates a large crater on
> an
> > Goldilocks Asteroid
> > which works.. ..
> >
> >
> >
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Received on Mon 07 Sep 2009 09:18:29 PM PDT