Scientists Find That Earth and Mars are Different to the Core
baa...@earthlink.net
Scientists find that Earth and Mars are different to the core
Science and Technology Facilities Council
June 28, 2007
Research comparing silicon samples from Earth, meteorites and
planetary
materials, published in Nature (28th June 2007), provides new evidence
that the Earth's core formed under very different conditions from
those
that existed on Mars. It also shows that the Earth and the Moon have
the
same silicon isotopic composition supporting the theory that atoms
from
the two mixed in the early stages of their development.
This latest research which was carried out by scientists from Oxford
University along with colleagues from University of California, Los
Angeles (UCLA) and the Swiss Federal Institute of Technology in Zurich
(ETH) compared silicon isotopes from rocks on Earth with samples from
meteorites and other solar system materials. This is the first time
that
isotopes have been used in this way and it has opened up a new line of
scientific investigation into how the Earth's core formed.
On Earth rocks that make up volcanoes and mountain ranges and underlie
the ocean floor are made of silicate - compounds made of silicon and
oxygen linked with other kinds of atoms. Silicate dominates down to a
depth of 2,900 km - roughly half way to the centre of the Earth. At
this
point there is an abrupt boundary with the dense metallic iron core.
Studies by Birch in the 1950's demonstrated that the outer core had a
density too low to be made of pure iron and that it must also be made
up
of some lighter elements (see notes to editors for further details).
Research team member, Bastian Georg, a post doctoral researcher from
Oxford University's Earth Sciences Department said, "We dissolved
meteorites, provided by the Natural History Museum in London, in order
to compare their isotopic composition with those of rocks from the
Earth. The silicon was separated from other elements and the atomic
proportions of isotopes measured using a particularly sophisticated
mass
spectrometer at the ETH in Zurich".
Professor Alex Halliday, also from Oxford University explains, "We
were
quite startled at our results which showed that the heavier isotopes
from silicate Earth samples contained increased proportions of the
heavier isotopes of silicon. This is quite different from meteorites
from the silicate portions of Mars and the large Asteroid Vesta -
which
do not display such an effect even though these bodies also have an
iron
core."
Silicate samples from Mars and Vesta are identical to a primitive
class
of meteorites called chondrites that represent average solar system
material from small "planetesimals" that never underwent core
formation.
Professor Halliday continues, "The most likely explanation is that,
unlike Mars and Vesta, the Earth's silicon has been divided into two
sorts - a portion that became a light element in the Earth's core
dissolved in metal and the greater proportion which formed the
silicon-oxygen bonded silicate of the Earth's mantle and crust."
At depths the silicates change structure to denser forms so the
isotopic
make-up would depend on the pressure at which metal and silicate
separate. Quantifying this effect is the subject of ongoing studies.
Co-author on the paper Edwin Schauble from UCLA, has produced
preliminary calculations that show that the isotopic effects found are
of the right direction and magnitude.
This research provides new evidence that the Earth's core formed under
different conditions from those that existed on Mars. This could be
explained in part by the difference in mass between the two planets.
With Earth being eight times larger than Mars the pressure of core
formation could be higher and different silicate phases may have been
involved. The mass of a planet also affects the energy that is
released
as it accretes (or grows).
The Earth accreted most of its mass by violent collisions with other
planets and planetary embryos. The bigger the planet, the greater the
gravitational attraction and the higher the temperatures that are
generated as the kinetic energy of impacting objects is converted to
heat. Some have proposed that the outer Earth would have periodically
become a "magma ocean" of molten rock as a result of such extreme high
temperature events.
There is evidence that Mars stopped growing in the first few million
years of the solar system and did not experience the protracted
history
of violent collisions that affected the Earth. There already exists
compelling evidence for relatively strong magnetic fields early in
martian history but a thorough understanding of the martian core must
await geophysical measurements by future landers. It is however
thought
that the core of Mars is proportionally smaller than that of the Earth
and it probably formed under lower pressures and temperatures.
The research also shows that the Moon has the same silicon isotopic
composition as the Earth. This cannot be caused by high pressure core
formation on the Moon which is only about one percent of the mass of
the
Earth. However, it is consistent with the recent proposal that the
material that made the Moon during the giant impact between the
proto-Earth and another planet, usually called "Theia", was
sufficiently
energetic that the atoms of the disk from which the Moon formed mixed
with those from the silicate Earth. This means the silicon in the
silicate Earth must have already had a heavy isotopic composition
before
the Moon formed about 40 million years after the start of the solar
system.
The research was supported from grants provided by the UK's Science
and
Technology Facilities Council, and the USA's and Switzerland's
National
Science Foundation.
Contacts
Gill Ormrod - Science and Technology Facilities Council Press Office
Tel: 01793 442012. Email: gill....@stfc.ac.uk
Pete Wilton - Oxford University Press Office
Tel: 01865 283877
Email : pete....@admin.ox.ac.uk
UK Science contact
Professor Alex Halliday - Department of Earth Science, Oxford
University
Tel: 07769728153
Email: al...@earth.ox.ac.uk
Notes to Editors
The information in this release in based on the following Nature
paper,
which appears in 28th June issue.
Silicon in the Earth's core
R Bastian Georg 1,2, Alex N. Halliday 1, Edwin A Schauble 3 and Ben C
Reynolds 2.
1. Department of Earth Sciences, University of Oxford 2. Department of
Earth Sciences, ETH Zentrum, Zurich 3. Department of Earth and Space
Science, University of California, Los Angeles.
In 1952 the distinguished Harvard geophysicist Francis Birch showed
that
the Earth's liquid outer core, where the magnetic field is generated,
is
chemically different from the solid metallic iron inner core that
occupies the very centre of the Earth. Birch argued that the outer
core
had a density that was too low to be made of pure iron; it had to
contain several percent of a lighter element or elements of lower
atomic
weight. Since then scientists have sought to determine what these
light
elements are and what their concentrations tell us about the
conditions
of core formation.
The Science and Technology Facilities Council ensures the UK retains
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SBC Yahoo
<baa...@earthlink.net> wrote in message
news:1183048116.3...@i38g2000prf.googlegroups.com...
Very interesting. Perhaps mars never had a plate system like earth, but if
it did, and the above is kosher, it was a bit different from our
core-mantle-crustal plate movement system, I would guess. But one thing is
for certain, today, mars is geologically dead. No volcanoes, no plate
movement.
I had always been told that Si (silicon) did not form in nature, but if
isotopes of silicon were found, perhaps it does, at extreme depths and
temps?
Sounds like a good show for the Science Channel.
George
Thanks for posting this, Ron. It answers a lot of my questions.
George
Jan Panteltje
baa...@earthlink.net wrote in
<1183048116.3...@i38g2000prf.googlegroups.com>:
>Silicate samples from Mars and Vesta are identical to a primitive
>class of meteorites called chondrites that represent average solar system
>material from small "planetesimals" that never underwent core
>formation.
>
>Professor Halliday continues, "The most likely explanation is that,
>unlike Mars and Vesta,
The _most_ likely explanation is that he meteorites were not from mars
in the fist place.
We need real samples
George
"Jan Panteltje" <pNaonSt...@yahoo.com> wrote in message
news:f60tvr$4jd$1...@aioe.org...
We'll wait here while you go get some.
George
Odysseus
"SBC Yahoo" <atilla....@liberals.suck.net> wrote:
<snip>
>
> I had always been told that Si (silicon) did not form in nature, but if
> isotopes of silicon were found, perhaps it does, at extreme depths and
> temps?
From my reading of the article I got the impression that it isn't a case
of different isotopes being formed, but that the primordial
(supernova-produced?) mixture of isotopes gets modified in different
ways in various physical/chemical environments. I suppose one might
think of a phase boundary in a planet's interior as a gigantic
chromatographic apparatus, tending to separate those isotopes that
prefer to exist in one phase or the other.
--
Odysseus
Aidan Karley
> The _most_ likely explanation is that he meteorites were not from mars
> in the fist place.
> We need real samples
>
the identification of certain meteorites as being form Mars is quite
secure. The process of impact spalling fragments off the surface also
melts small amounts of the rock on slip planes, fracture surfaces etc
(unsurprisingly), and the high pressures in the impact drives bubbles of
gas into this glass. Onec the rock fragment has wandered through space
for a few millennia it hits the Earth's atmosphere, the surface is
heated for a couple of seconds, then it crumps down into Antarctic snow
or an Egyptian dog (allegedly, for the Nakhla meteorite) and is
eventually found by a meteorite hunter. When the gas bubbles are
identified in microscope thin sections (well, "thick sections" ; about
0.1mm, polished but no cover slip) and zapped with an ion microprobe
beam, the gas composition can be measured ... and is found to have a
stable isotope composition matching that measured by the Viking landers,
not what we find on Earth.
If you're interested, I've got the papers detailing the process
somewhere.
Identification of Vesta-derived meteorites is a bit less secure,
based on the IR reflection spectrum of the fresh meteorite surfaces
matching that of Vesta. Once the plausibility of the process had been
established by the identification of the Martian meteorites, the
identification of other meteorites with Vesta had much less resistance.
Plus, there are a number of asteroids in related orbits to Vesta which
are interpreted as debris from a recent (last few million years) large
impact on Vesta.
The lunar-derived meteorites are uncommon, but securely
identified by correlation against Apollo samples.
--
Aidan Karley, FGS,
Aberdeen, Scotland
A light wave is more like a crime wave than a water wave.
Aidan Karley
> Perhaps mars never had a plate system like earth, but if
> it did, and the above is kosher, it was a bit different from our
> core-mantle-crustal plate movement system, I would guess.
early in Mars history. A little south of the equator and covering a bit less
than a quadrant of the equator, there is an area of parallel lines of differing
magnetic intensity which is cross-cut and little affected by the cratering, so
pre-dates the cratering. That puts it sometime between 4565 million years
(construction of the planets) and approximately 3800 million years (end of the
Late Heavy Bombardment, from Lunar impact metamorphism ages). And it
*looks* very like the classic Reykjanes Ridge magnetic anomaly pattern.
However ... with Mars being so much smaller than the Earth, the internal
temperatures are much lower, the initial heating by accretion much lower. Which
changes pretty much all the details from a plate tectonic point of view.
> But one thing is
> for certain, today, mars is geologically dead. No volcanoes, no plate
> movement.
>
Almost certain. The recently announced (suspected) "skylight" openings
into Martian lava tubes suggests that there's still some geological life in
there ; there have been reports of transient clouds on the summits of the
Tharsis volcanos which may be out-gassing ; the annual (Mars years!) movement
of mass from one pole to the other is bound to have some effect ; and of
course, there's the continuing aeolian deposition and re-working. This parrot
hasn't quite fallen off it's perch. Yet.
Timberwoof
Aidan Karley <name1...@email.provider.invalid> wrote:
> In article <c6Sgi.4622$vi5....@newssvr17.news.prodigy.net>, SBC
> Yahoo wrote:
> > Perhaps mars never had a plate system like earth, but if it did,
> > and the above is kosher, it was a bit different from our
> > core-mantle-crustal plate movement system, I would guess.
> There is (disputed) evidence for something plate-tectonic-like
> happening
> early in Mars history. A little south of the equator and covering a
> bit less than a quadrant of the equator, there is an area of parallel
> lines of differing magnetic intensity which is cross-cut and little
> affected by the cratering, so pre-dates the cratering.
You mean there are craters in the region, but no magnetic anomalies
correlate with them?
> That puts it
> sometime between 4565 million years (construction of the planets) and
> approximately 3800 million years (end of the Late Heavy Bombardment,
> from Lunar impact metamorphism ages).
Just how did they date the periods of bombardment?
> And it *looks* very like
> the classic Reykjanes Ridge magnetic anomaly pattern.
>
> However ... with Mars being so much smaller than the Earth,
> the internal
> temperatures are much lower, the initial heating by accretion much
> lower. Which changes pretty much all the details from a plate
> tectonic point of view.
Hm. I can understand a smaller body cooling off aster, but why would it
come to a lower temperature? Except for gravitational effects, aren't
its impacts as energetic as those into a larger body? Are those effects
what would account for that difference?
> > But one thing is for certain, today, mars is geologically dead. No
> > volcanoes, no plate movement.
> >
> Almost certain. The recently announced (suspected) "skylight"
> openings
> into Martian lava tubes suggests that there's still some geological
> life in there ; there have been reports of transient clouds on the
> summits of the Tharsis volcanos which may be out-gassing ; the annual
> (Mars years!) movement of mass from one pole to the other is bound to
> have some effect ; and of course, there's the continuing aeolian
> deposition and re-working. This parrot hasn't quite fallen off it's
> perch. Yet.
--
Timberwoof <me at timberwoof dot com> http://www.timberwoof.com
"When you post sewage, don't blame others for
emptying chamber pots in your direction." ‹Chris L.
an important web site: http://www.muslim-refusenik.com/
Henry Spencer
Aidan Karley <name1...@email.provider.invalid> wrote:
>...When the gas bubbles are identified
>in microscope thin sections ... and zapped with an ion microprobe
>stable isotope composition matching that measured by the Viking landers,
>not what we find on Earth.
Indeed, the match to Martian air is startlingly good. The meteorites with
the gas bubbles just have to have come from Mars; it would be much harder
to explain them originating anywhere else.
Only some of the Martian meteorites have such gas bubbles, but they are
all tied together into a family by things like odd mineralogies and
unusual oxygen-isotope ratios, so establishing that a few of them are from
Mars settles it fairly well for all of them. There is no longer any
reasonable doubt about this.
> If you're interested, I've got the papers detailing the process
>somewhere.
Try:
+ Bogard et al, "Noble gas contents of shergottites and implications
for the Martian origin of SNC meteorites", Geochim.Cosmochim.Acta
48:1723-1739, 1984.
+ Becker&Pepin, "The case for a Martian origin of the shergottites:
Nitrogen and noble gases in EETA 79001", Earth Planet Sci. Lett.
69:225-242, 1984.
+ Swindle et al, "Noble gases in SNC meteorites", Meteoritics 19:318-319,
1984.
+ Carr et al, "Martian atmospheric weathering products in SNC meteorites",
Nature 314:248-250, 1985.
> Identification of Vesta-derived meteorites is a bit less secure...
> The lunar-derived meteorites are uncommon, but securely
>identified by correlation against Apollo samples.
And there are one or two peculiar meteorites which perhaps might be from
Mercury, but we're unlikely to have confirmation of *that* for quite a
while, since we'd need (at the very least) surface analysis by a lander,
and none are planned.
--
spsystems.net is temporarily off the air; | Henry Spencer
mail to henry at zoo.utoronto.ca instead. | he...@spsystems.net
Jan Panteltje
<name1...@email.provider.invalid> wrote in
<VA.0000140...@email.provider.invalid>:
Thank you, sounds reasonable.
I made that remark inspired by yet an other posting in the trend of:
'and now we have to rethink completely about how planets and comets...'
as seen often posted by NASA in sci.astro.
Although I agree then methods you describe are very accurate with
a low margin of error I would personally like to see some
astronauts digging on mars :-)
It seems our view of how planets are formed is still changing, and that
would have some consequences for making statements where things come from.
No mars is not geologically dead, there is a picture somewhere of a geyser
like feature.. although some claim it is a dust devil...
We really need to go there an look.
Aidan Karley
<timberwoof.spam-C6...@nnrp-virt.nntp.sonic.net>,
> Just how did they date the periods of bombardment?
>
in-filled by crater counting. Some meteorites have poly-phase metamorphic
and/ or igneous textures that fit broadly within the "accumulation and
late heavy bombardment" model. It's not an exact science, but good enough
for give-or-take of a hundred million years.
> Hm. I can understand a smaller body cooling off aster, but why would it
> come to a lower temperature? Except for gravitational effects, aren't
> its impacts as energetic as those into a larger body? Are those effects
> what would account for that difference?
>
of the primary increases. Think of it the other way around : to raise a
1kilo meteorite off the Earth to "infinity" (or Pluto, which is an
approximation to infinity) will take a certain amount of energy ; double
the mass of the Earth and the same mass will need twice as much energy to
be raised to infinity. Turn the rocks around now and they'll return their
respective loads of kinetic energy to the planet they left.
The energy delivered per kilo of the primary (Earth, Mars,
whatever) doesn't change (within reason, assuming no gross changes in
density, but remember that Earth is also denser than Mars due to it's own
gravitational compression). But the region of space that is "hoovered
clean" by the planetesimals is bigger for bigger planetesimals, so the
lumps of kinetic energy arrive more frequently, the aggregating
planetesimal has less time to radiate from proportionately less surface
area before the next lump of kinetic energy impacts.
Aidan Karley
> And there are one or two peculiar meteorites which perhaps might be from
> Mercury, but we're unlikely to have confirmation of *that* for quite a
> while, since we'd need (at the very least) surface analysis by a lander,
> and none are planned.
>
something like 600 K towards noon? And a diurnal range of 400 K.
Severe.
Aidan Karley
> I made that remark inspired by yet an other posting in the trend of:
> 'and now we have to rethink completely about how planets and comets...'
> as seen often posted by NASA in sci.astro.
>
the operative words are "press release" ; there's a fine line to tread
between boring the pants off the intended audience (news editors) and
over-simplifying the science beyond what the egg-heads can stomach without
interrupting.
I regularly have to summarise what we're seeing in a well, whether the
geological objectives are being achieved, what the likely impact of today's
events would be on requirements for 3 days from now ... all without
confusing the audience of drillers, and often without actually telling them
anything that they don't *need* to know (because the well is "tight"). I can
appreciate the job that the man does - it's not easy.
> It seems our view of how planets are formed is still changing, and that
> would have some consequences for making statements where things come from.
>
Details are being elaborated, certainly, but the broad picture hasn't
significantly changed really in 20-something years. "Giant Impact" was the
last really significant lump to be added to the pot ; late addition of
volatiles by comets ... well, that's really been there all along (though
Giant Impact has brought whole-planet fusion back to the forefront).
Now, the level of detail that, for example, GRAPE computers can bring
to modelling the evolution of planetary systems and the process of turning
dust-clouds into planets ... that's impressive. But it's also just doing an
awful lot of Newton with a couple of Cook's Constants for adhesion,
inelasticity, etc.
Stuart
<timberwoof.s...@inferNOnoSPAMsoft.com> wrote:
> In article <VA.00001410.29af9...@email.provider.invalid>,
> Aidan Karley <name1_na...@email.provider.invalid> wrote:
>
> > In article <c6Sgi.4622$vi5.2...@newssvr17.news.prodigy.net>, SBC
> > Yahoo wrote:
> > > Perhaps mars never had a plate system like earth, but if it did,
> > > and the above is kosher, it was a bit different from our
> > > core-mantle-crustal plate movement system, I would guess.
> > There is (disputed) evidence for something plate-tectonic-like
> > happening
> > early in Mars history. A little south of the equator and covering a
> > bit less than a quadrant of the equator, there is an area of parallel
> > lines of differing magnetic intensity which is cross-cut and little
> > affected by the cratering, so pre-dates the cratering.
>
> You mean there are craters in the region, but no magnetic anomalies
> correlate with them?
>
> > That puts it
> > sometime between 4565 million years (construction of the planets) and
> > approximately 3800 million years (end of the Late Heavy Bombardment,
> > from Lunar impact metamorphism ages).
>
> Just how did they date the periods of bombardment?
Not with particularly great precision.
Basically I believe it is referenced to the moon and the few age
determinations of lunar rocks.
This then allows some dates to be assigned to the relative time scaled
infered from crater
studies.
Stuart
Henry Spencer
Aidan Karley <name1...@email.provider.invalid> wrote:
>> And there are one or two peculiar meteorites which perhaps might be from
>> Mercury, but we're unlikely to have confirmation of *that* for quite a
>>
> Be a bit harsher for them than for the Mars rovers. What is it -
>something like 600 K towards noon? And a diurnal range of 400 K.
> Severe.
Indeed, Mercury is a harsh environment even for *orbiters*, never mind
landers.
(If your orbit passes low over the sunlit side, *half the sky* is full of
oven-hot planet -- a far worse thermal problem than just having rather
brighter sunlight. This is why Mercury-orbiter designs tend to use quite
elliptical orbits: most science instruments would benefit from more time
down low, but the thermal environment is just horrible, and reasonable
spacecraft designs have to spend most of their time higher up so they can
cool off. An orbit over the terminator -- the day-night boundary -- would
be much better, although even there you'd probably want it to be somewhat
elliptical, but there's no way to *keep* an orbit over the terminator for
long without advanced propulsion. A solar sail actually would work very
nicely for this...)
On the surface, you can probably reduce both the peak temperature and the
temperature swing by landing near one of the poles... but things still get
pretty chilly at night.
ESA's BepiColombo mission originally included a small lander, but alas,
that got deleted to keep the budget under control.
BradGuth
wrote:
> The lunar-derived meteorites are uncommon, but securely
> identified by correlation against Apollo samples.
There's no such thing as an uncommon lunar-derived sample. They'd
have to be everywhere you'd care to look. Where the hell else would
that sort of displaced mega, giga if not teratonnage have gone?
- Brad Guth