On Mar 20, 9:28 am, don findlay <d...@tower.net.au> wrote:
Darwin123 wrote:
It would be so nice if scientific documentaries included
references to scientific papers, even if most of the audience don't
care. I am sure that few of the audience care about the actors,
writers and directors. Yet we have credits.

Surely you don't think the credits are for the benefit of the viewer,
do you?

No, they are for the cast. Actors get additional exposure so
people know their names. Furthermore, it provides a chain of reference
on their resumes. A future employer, looking at their resume, can look
at their work and get additional verification on their participation
in the product. The same applies for directors, writers, special
effects people, etc.
Citing the scientific article would benefit the scientist that
wrote them. It is the nonscientist who is going to hire them, after
all.
I don't see any published code of ethics that forbids publicity
once the peer review has gone through. One of the bad things about
popularized science on TV is that there is no way a better informed
viewer can look at the details.
I would love to know the assumptions that went into that
simulation. I don't know what I am discussing unless there is some
exposition on the physics involved. The result of a computer
simulation is merely a cartoon without the physical and mathematical
assumptions that went into the simulation. Without physics, historical
conjecture is stupid. Especially in natural history.

Yeah, I made the same mistake. For future reference, Florian. It would help
if you posted a link to the entire article so we can know the context of the
graphs you are referrring to.

But you are right in the sense that the graph
doesn't show a decrease in volcanic activity. But it doesn't show an
increase either. It only shows that the volcanic activity has been widely
distributed and sporatic in time as indicated by continued loss of craters
due to lava flows.

The article makes the point that all the internal heat
within Mars may not have yet dissipated, but it doesn't say that it is
currently active. Only suggests that there could be further activity on the
planet.

I think it is possible that some very minor activity could occur in
the furture. But there certainly is no evidence that large scale vulcanism
has occurred in recent times.

It certainly appears to make the case that
although Mars may still be tectonically active, it is subtle, probably order
of magnitude less active than Earth,

which would indicate that Mars interior
certainly isn't the dynamo that Earth's interior is.

Timberwoof wrote:

.... where did
the iron in Earth come from?

Handy lumps.  Ask bradhttp://tinyurl.com/yv3tb4

"Skywise" <i...@oblivion.nothing.com> wrote in message

news:13u10vvtoo55d71@corp.supernews.com...

rAgAv <ragav.pa...@googlemail.com> wrote in news:1ffef2dc-a033-410e-96f4-
4f0136740...@e6g2000prf.googlegroups.com:

Hello,

According to my current knowledge, the earth's magnetic field formed
due to the molten iron core that is spinning to create a magnetic
field. This magnetic field is also what is protecting us from harmful
bursts (solar plasma?) from the sun.

I don't understand one thing - why doesn't Mars have one?

Mars is cold. Being smaller, it cooled quicker. It's liquid
core froze eons ago thus shutting down its dynamo.

But then why does Venus not have one?  Being roughly the same size as Earth
and all................
cheers
Bill

On Mar 19, 4:22 pm, "Landy" <no...@nowhere.net> wrote:> "Timberwoof" <timberwoof.s...@inferNOnoSPAMsoft.com> wrote in message

news:timberwoof.spam-30CDC8.09083319032008@nnrp-virt.nntp.sonic.net...

In article <gfWdnSyiUOCYYn3anZ2dnUVZ_u6rn...@comcast.com>,
John Popelish <jpopel...@rica.net> wrote:

Why would that event suddenly leave the iron core in the

Earth and not leave one in the moon?

Because it had greater momentum and was less likely to vapourise.
cheers
Bill

    The sentence doesn't quite make sense. Do you mean momentum in the
center of mass coordinate system of the two bodies? Furthermore, why
would greater momentum make it less likely to vaporize?
       I saw a special describing the results of the simulation but
they didn't try to explain the results in simpler terms.
     My first guess was that the two bodies merged for a short time
into one giant liquid body, and partially equilibrated. Then, there
would be forces that resembled buoyancy. Basically, the iron sunk to
the bottom of the merged body.
    Wait, this doesn't work (?). The system would be far too
turbulent. The Froude number would be too big to allow stratification.
     My second guess involves phase transitions. The joint body was
gas. The iron, having a higher vaporization temperature, condensed
into one massive liquid-body that sent all the momentum into the gas,
which then recondensed into the moon. The elements with the small
atomic number had larger vaporization point temperatures.
     Calculations have long shown, since the 1700s, that an inelastic
collision between earth-like bodies would vaporize most of the
material of both bodies. Therefore, I would hope the simulation
included phase transitions in the dynamics. Did they?
      The verbal description only said they simulated the bodies as
made of many small particles, and calculated separate trajectories.
There are google squared ways to do this.

     What bothers me is that the computer simulation never means
anything by itself. It is the physical assumptions being made that
make the computer simulation meaningful. You can't go, "Run a computer
simulation," and believe everything that comes out. If you don't
confined the physics before the run, you can make the physics do
ANYTHING.
    It would be so nice if scientific documentaries included
references to scientific papers, even if most of the audience don't
care. I am sure that few of the audience care about the actors,
writers and directors. Yet we have credits.

"Skywise" <i...@oblivion.nothing.com> wrote in message

news:13u10vvtoo55d71@corp.supernews.com...

rAgAv <ragav.pa...@googlemail.com> wrote in news:1ffef2dc-a033-410e-96f4-
4f0136740...@e6g2000prf.googlegroups.com:

Hello,

According to my current knowledge, the earth's magnetic field formed
due to the molten iron core that is spinning to create a magnetic
field. This magnetic field is also what is protecting us from harmful
bursts (solar plasma?) from the sun.

I don't understand one thing - why doesn't Mars have one?

Mars is cold. Being smaller, it cooled quicker. It's liquid
core froze eons ago thus shutting down its dynamo.

But then why does Venus not have one?  Being roughly the same size as Earth
and all................
cheers
Bill

Stuart <bigdakine@aol.com> wrote:

On Mar 22, 11:18 pm, auxotectonics_deletethis@nachon_andthis.net
(Florian) wrote:
Stuart <bigdak...@aol.com> wrote:
I wonder if you worth more than Georgie... I remember you were the
one
stating that buoyancy is not related to pressure gradient. What a
pity.

I said hydrostatic gradient was irrelevant.

Do you agree that the lithostatic pressure gradient is relevant, yes or
no?

Lithostatic refers to the same thing.

Technically not.

Hydrostatic pressure in geology, usually refer to the pressure of the
fluid in the cracks, fractures, porosity in the upper crust.

Lithostatic pressure refer to the pressure caused by the column of rock.

Now Stuart, could you please answer to this simple question, a question
that is trivial for a geophysicist who developped a computer model of
convection.

Do you agree that the lithostatic pressure gradient is relevant to
buoyancy, yes or no?


[...]

Anyway, I remember clearly that the discussion was about the
inititation
of subduction. What makes a slab sink if its density is initially
higher
than that of the upper mantle?

Is that really the question you mean to ask?

It was the object of the original discussion, Stuart. May be that time
plays tricks on your mind...

--
Florian
"Toute vérité passe par trois phases. D'abord, elle est ridiculisée;
ensuite, elle rencontre une vive opposition avant d'être acceptée comme
une totale évidence" - Arthur Schopenhauer

George <George@george.net> wrote:

Yeah, I made the same mistake. For future reference, Florian. It would
help
if you posted a link to the entire article so we can know the context of
the
graphs you are referrring to.

more eyes rolling

The link to the article was posted in the thread in :

news:1ie1tyx.kov73012akbdoN%auxotectonics_deletethis@nachon_andthis.net

But you are right in the sense that the graph
doesn't show a decrease in volcanic activity. But it doesn't show an
increase either. It only shows that the volcanic activity has been widely
distributed and sporatic in time as indicated by continued loss of
craters
due to lava flows.

Hmmm, I see nowhere in the article, a mention that craters are loss by
lava flow...

The article makes the point that all the internal heat
within Mars may not have yet dissipated, but it doesn't say that it is
currently active. Only suggests that there could be further activity on
the
planet.

Indeed. My point was that Mars might not be dead in contrast to the
statement made by SBC Yahoo, in this thread.

I think it is possible that some very minor activity could occur in
the furture. But there certainly is no evidence that large scale
vulcanism
has occurred in recent times.

It depends on what you mean by "recent time". On a 4.5 billions years
time scale, 100 millions is quite recent.
Besides there is a clear trend: The frequency of major volcanic events
has increased, the rest period being basically divided by two after each
events.

It certainly appears to make the case that
although Mars may still be tectonically active, it is subtle, probably
order
of magnitude less active than Earth,

You're guessing. We won't know before some guys put a sismometer there.

which would indicate that Mars interior
certainly isn't the dynamo that Earth's interior is.

We know that Mars magnetic field is weaker than that of the Earth, for
sure.

Hmmm, I see nowhere in the article, a mention that craters are loss by
lava flow...

Then perhaps you need to understand what the article is all about.

For instance:

"A new analysis of impact cratering data from Mars reveals that the planet
has undergone a series of global volcanic upheavals. These violent episodes
spewed lava and water onto the surface, sculpting the landscape that ESA's
Mars Express looks down on today.

Using images from the High Resolution Stereo Camera (HRSC) on Mars Express,
Gerhard Neukum, Freie Universität Berlin, Germany, and colleagues are
discovering the history of the Red Planet's geological activity. "We can now
determine the ages of large regions and resurfacing events on the planet,"
says Neukum. Resurfacing occurs when volcanic eruptions spread lava across
the planet's surface."

In other words, volcanic activity has resurfaced the planet, and in doing
so, has erased many prior impacts.

That is largely why over time, the graph
shows a DECREASE in impacts - because the surface has been resculpted by
volcanic activity.

It depends on what you mean by "recent time". On a 4.5 billions years
time scale, 100 millions is quite recent.
Besides there is a clear trend: The frequency of major volcanic events
has increased, the rest period being basically divided by two after each
events.

There is NO evidence in that article that indicates whether volcanic
activity has increased or decreased. From what I can tell from what was
presented in the article, that issue wasn't even addressed.

If I am guessing, then so are the authors of the article, since my statement
is essentially the same statement they made.

George <George@george.net> wrote:

Hmmm, I see nowhere in the article, a mention that craters are loss by
lava flow...

Then perhaps you need to understand what the article is all about.

From a guy who can't read a simple chart. Give me a break.

For instance:

"A new analysis of impact cratering data from Mars reveals that the
planet
has undergone a series of global volcanic upheavals. These violent
episodes
spewed lava and water onto the surface, sculpting the landscape that
ESA's
Mars Express looks down on today.

Using images from the High Resolution Stereo Camera (HRSC) on Mars
Express,
Gerhard Neukum, Freie Universität Berlin, Germany, and colleagues are
discovering the history of the Red Planet's geological activity. "We can
now
determine the ages of large regions and resurfacing events on the
planet,"
says Neukum. Resurfacing occurs when volcanic eruptions spread lava
across
the planet's surface."

In other words, volcanic activity has resurfaced the planet, and in doing
so, has erased many prior impacts.

Here again, you assume that the volcanic events resurfaced a large
portion of Mars. But you simply can't guess it from the paper.

Anyway, you completely fail to understand the principle of craters
counting.

Craters counting allow to estimate the age of an area, even one of a few
hundred square km, by counting the number of craters per square km. Note
that it is a DENSITY of craters, not an absolute number. The larger the
number of craters per square km, the older is the area, whatever the
size of the resurfaced area.

That is largely why over time, the graph
shows a DECREASE in impacts - because the surface has been resculpted by
volcanic activity.

Seriously, do you really suggest that the decrease of impact craters
density is not related to the decrease in meteorites density in the
solar system?? Do you know that impact craters density follow the same
trend on the moon? May be you also suggest that the moon was resurfaced
by volcanic event as well?

It depends on what you mean by "recent time". On a 4.5 billions years
time scale, 100 millions is quite recent.
Besides there is a clear trend: The frequency of major volcanic events
has increased, the rest period being basically divided by two after
each
events.

There is NO evidence in that article that indicates whether volcanic
activity has increased or decreased. From what I can tell from what was
presented in the article, that issue wasn't even addressed.

Let's look at the graph. Major episodes occured at 3500, then 1500 then
400-800, then 200 then 100 million years, but you still can't figure out
that the frequency of episodes increased with time? You're hopeless...


[...]

If I am guessing, then so are the authors of the article, since my
statement
is essentially the same statement they made.

No George. The authors of the article present data showing that the
activity on Mars is episodic and at a frequency that increased.
No guess just facts.

Anyway, you completely fail to understand the principle of craters
counting.

Craters counting allow to estimate the age of an area, even one of a few
hundred square km, by counting the number of craters per square km. Note
that it is a DENSITY of craters, not an absolute number. The larger the
number of craters per square km, the older is the area, whatever the
size of the resurfaced area.

And your point is what, exactly?

Seriously, do you really suggest that the decrease of impact craters
density is not related to the decrease in meteorites density in the
solar system?? Do you know that impact craters density follow the same
trend on the moon? May be you also suggest that the moon was resurfaced
by volcanic event as well?

Comparing the moon with Mars is like comparing apples and oranges. The moon
has not substantially changed since the major bombardments early in it's
history. The surface of Mars HAS changed substantially since then.

George <Geo...@george.net> wrote:
Anyway, you completely fail to understand the principle of craters
counting.

Craters counting allow to estimate the age of an area, even one of a few
hundred square km, by counting the number of craters per square km. Note
that it is a DENSITY of craters, not an absolute number. The larger the
number of craters per square km, the older is the area, whatever the
size of the resurfaced area.

And your point is what, exactly?

That you're a moron not capable to understand that the age is derived
form the DENSITY of craters, not from the number of craters that would
have been erased by spewed lava.

Seriously, do you really suggest that the decrease of impact craters
density is not related to the decrease in meteorites density in the
solar system?? Do you know that impact craters density follow the same
trend on the moon? May be you also suggest that the moon was resurfaced
by volcanic event as well?

Comparing the moon with Mars is like comparing apples and oranges. The moon
has not substantially changed since the major bombardments early in it's
history. The surface of Mars HAS changed substantially since then.

More moronic comments. The cratening rate of the Moon like Mars or any
object in the inner solar system is assumed to be similar.

Here is a little exercise that you will certainly fail to resolve:

http://www.astro.washington.edu/larson/Astro150b/CoursePak/cp14_crater_
counting.pdf

If you have a massive lava flow it will reduce the crater density by
burying the craters.

On an object like the moon, we knew that the Mare were younger than the
highlands before any rocks were brought back. Why because they had a lower
crater density than any place else. Why? because the flood basalts that
comprise the Mare buried the craters in effect resetting the crater
density based chronometer.

George's point flew right over your head.

You can assume the bombardment of the moon and other bodies was similar.
Probably not a great assumption, but better than an order of magnitude.

On Mar 23, 4:58 am, auxotectonics_deletethis@nachon_andthis.net
(Florian) wrote:
Stuart <bigdak...@aol.com> wrote:
On Mar 22, 11:18 pm, auxotectonics_deletethis@nachon_andthis.net
(Florian) wrote:
Stuart <bigdak...@aol.com> wrote:
I wonder if you worth more than Georgie... I remember you were
the one

fluid in the cracks, fractures, porosity in the upper crust.

Lithostatic pressure refer to the pressure caused by the column of rock.

"Same difference in the sense that neither cause fluid motion", both are
cases
of a spherical stress tensor.
SNIP
Stuart

Stuart <bigdak...@aol.com> wrote:
If you have a massive lava flow it will reduce the crater density by
burying the craters.

On an object like the moon, we knew that the Mare were younger than the
highlands before any rocks were brought back. Why because they had a lower
crater density than any place else. Why? because the flood basalts that
comprise the Mare buried the craters in effect resetting the crater
density based chronometer.

Explain that to Georgie who is apparently convinced "that the volcanic
activity has been widely distributed and sporatic in time as indicated
by continued loss of craters due to lava flows." (sic!)

or again:

"In other words, volcanic activity has resurfaced the planet, and in
doing so, has erased many prior impacts. That is largely why over time,
the graph shows a DECREASE in impacts - because the surface has been
resculpted by volcanic activity."

See, you're buddy truly think that the graph shows a decrease in impacts
because of the lava flow resetting the surface, whereas the graph show a
decrease in the DENSITY of craters because there is simply less
asteroids that impacts as time goes by.

Even highschooler know that the frequency of asteroid impacts decrease
with time in the inner solar system.

For sure, If the frequency had been constant with time, that would have
been much easier to date surfaces, but that is not he case (see the work
of Hartmann, Neukum and Ivanov cited below.)

George's point flew right over your head.

Give me a break. See above. I don't even understand why you try to save
the scalp of a moron that can't understand an article nor read a graph
legend.

You can assume the bombardment of the moon and other bodies was similar.
Probably not a great assumption, but better than an order of magnitude.

"I" don't assume. This assumption was made and jsutified by Neukum
Ivanov and Hartmann to date the surface of Mars from Moon's data. See
in:

Hartmann, W. K. and Neukum, G. (2001) Space Sci. Rev. 96, 165-194

http://www.springerlink.com/content/nq62226301355207/?p=9e21e16db846498
0a499db540cf257fd&pi=8

for a recent work ans some graph illustrating the coorelation:

http://www.lpi.usra.edu/meetings/lpsc2008/pdf/2509.pdf

May be you would like to deny their work?

I wonder if you worth more than Georgie... I remember you were the one
stating that buoyancy is not related to pressure gradient. What a pity.