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back to article ROCK FROM MARS FOUND in Africa, reveals Red Planet's SECRETS

Boffins have dated a piece of Martian meteorite they reckon is the oldest bit of the planet ever collected. Martian meteorite NWA7533 Radioactive analysis of the zircons in NWA7533, a meteorite found in Northwest Africa, have revealed that the rock is around 4.4 billion years old - so it was formed just 100 million years …

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Anonymous Coward

Ok, excuse me for asking but HTF do they know it is from Mars?

As no Human has (to our knowledge and with Dr Who's assistants excluded) set foot on the Red Planet how can they really 100000000% know that it came from Mars?

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Re: Ok, excuse me for asking but HTF do they know it is from Mars?

Because it doesn't look like ones from Uranus!

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Silver badge

Re: Ok, excuse me for asking but HTF do they know it is from Mars?

On the back of the rock there is a small inscription

"Made in Mars ( by the PRC)"

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Bronze badge

Re: Ok, excuse me for asking but HTF do they know it is from Mars?

But its a good question: The only thing we can compare those rocks to, is current data from our mars rovers, or recent meteorites with trajectories confirmed to be originating from mars. Also of course atmospheric measurements by either orbiters, rovers or spectral analysis from earth or earth orbit, but they can't confirm what mars' composition was 4.x billion years ago, afaik.

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Happy

Re: Ok, excuse me for asking but HTF do they know it is from Mars?

How can you be 100000000% certain the rocks in your backyard came from Earth? How can you be 1000000000% certain the rocks in your backyard are really there? :)

They determined the rock was from Mars by comparing its composition to the data we have about Martian rocks. The rock obviously isn't from Earth and its composition matches that of Mars so well that any other possibility becomes enormously more unlikely with every hypothesis.

You start getting into weird theoretical situations like comets colliding and the resultant debris from both are amalgamated under the enormous force of the impact and part of it lands on Earth and just happens to be the same composition as Martian rocks. Like I said, weird and extraordinarily unlikely.

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Silver badge

Re: Ok, excuse me for asking but HTF do they know it is from Mars?

It's down to overall ratios of trace elements compared to known (current) ratios on the various planets.

It's never 100% conclusive because some other solar body could just happen to have a make up, or region, that is similar enough to Mars that a bit of it knocked off that happens to land on Earth could match.

The formation and type of rock can help determine if it came from a planet or not (formation under gravity is very different to under low or none) and trapped atmospheric gasses are also indicative of where a rock initially formed. Where there are trapped atmospheric gasses the list of sources is quite short (few planets / planetoids have ever had or have an atmosphere) and they are quite different from each other.

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Bronze badge

Re: Ok, excuse me for asking but HTF do they know it is from Mars?

Humans have set plenty of little scurrying robot feet on Mars, and plenty of orbiters. Between the two, we're getting a pretty good map of Martian minerals, isotope ratios, and general geology. "Black Beauty" has a chemical and isotopic composition quite similar to the southern highlands of Mars and nothing quite like Earth.

The end result is some room for doubt, not 100000000% certain, but it is certain that rock ain't from around here.

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Anonymous Coward

Re: Ok, excuse me for asking but HTF do they know it is from Mars?

The model number on it matches the catalogue entry in the sales brochure from Magrathea.

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Re: Ok, excuse me for asking but HTF do they know it is from Mars?

Often it's done by comparing the composition of gas bubbles within the rock to measurements of the Martian atmosphere obtained from Soviet and American Mars landers. If that can't be done then it's a process of elimination. Isotope ratios will not match those of the Earth and Moon. The mineralogy is often quite evolved and can incorporate hydrous minerals, and will not match that of the Moon or regular stony meteorites. They have a *relatively* young crystallisation age determined by radio dating will not match that of stony meteorites, and the effect of cosmic ray bombardment usually shows they have been in space for only a few million years.

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Anonymous Coward

Re: Ok, excuse me for asking but HTF do they know it is from Mars?

They are experts. Why wouldn't they?

(By the way., whomever assigned my screen name, I must say touché. I also love the V for Vendetta mask; great film!)

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Joke

Re: Ok, excuse me for asking but HTF do they know it is from Mars?

Maybe they asked Stephen Hawking....

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Re: Ok, excuse me for asking but HTF do they know it is from Mars?

Good point. We do not know where it came from. They do not know. In any case the Martian surface they now explore is a highly altered "new surface" a few million to 1 or 2 billion years old, not a 4.5 billion year old pristine surface of an asteroid. We cannot compare the NOW surface chemistry of Mars with the chemistry of a meteorite fro who knows where.

Chris Landau (geologist) November 22, 2013

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Trashy Planets

Wouldn't that mean there are bits of Earth laying around the cosmos, possibly even to be found on Mars? At least, before our atmosphere was formed?

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Re: Trashy Planets

Yep, bits of Earth could be on other planets and moons (especially Luna). It's a bit more challenging to get bits of Earth elsewhere, owing to Earth's higher escape velocity, but I'm sure it's happened.

I mean, in the extreme, current theories of Luna's formation say it's a big gobbet of Earth-Theia crust and mantle. So the moon is kind of a big bit of Earth.

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Boffin

Re: Trashy Planets

Bits of planets on other planets would tend to be found further in towards the Sun than the planet they came from. Although not impossible, the amount of Earth material on Mars would be minuscule compared to the reciprocal case. One could assume Mars material on Venus and Mercury, a lot less* Earth material on Venus and Mercury (see comments above about escape velocity), etc.

*notwithstanding the theorised cataclysm that created the Moon

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Boffin

Re: Trashy Planets

This came up just the other day, in fact (specifically about the Chixulub impact, though):

https://medium.com/the-physics-arxiv-blog/56e227224a25

Earlier studies also showed significant probabilities of dispersal to other Solar System bodies:

http://arxiv.org/abs/1108.3375

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NWA

NWA7034 ?

Surely it came 'Straight Outta Compton' ?

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Childcatcher

Re: NWA

Dam Martian kids...first, they short out the rover's electrics, now they're chucking rocks at us?

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Alert

Young?

"the rock is around 4.4 billion years old - so it was formed just 100 million years after Mars itself. In planetary terms, this is very young indeed." Surely, while young in terms of the Universe, it is very old in planetary terms if it is only 100 million years younger than Mars itself?

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Coat

Dating is easy, i did it in school.

And So :

the reason we know how old it is, is that as you can see by estimating the circumference and the distance between the rings, that mars at the time was about 20 meters across, and approximately 100m years old.

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Bronze badge

It's being able to estimate the thickness of the Martian crust that I find amazing

"In addition, incompatible element abundances in clast-laden impact melt rocks and interclast matrix provide a geochemical estimate of the average thickness of the Martian crust (50 kilometres) comparable to that estimated geophysically" is what the abstract says. Fascinating though that sounds, I am not about to spend 22 on the whole article.

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There are a couple of things that worry me about all the meteorites coming out of North West Africa. I know it is a desert, but there are other deserts for preservation purposes. I worry about scams going on. Secondly, It is extremely rare to find a rock on Earth older than about 4.0 billion years old. Just as Earth's surface has been reworked, so has the surface of Mars. What we look at today is younger rocks. It is laughable to think that you can tell the exact chemistry, mineralogy or age from a vast suite of rocks by scanning from satellite. The scan of Vesta in 2012 is a case in point. (HED meteorites from Vesta very vague). I had enough trouble telling one mineral from another under a petrographic microscope and to sweep large sections of the planet Mars as the same smacks of huge arrogance or stupidity or both. Mineralogy varies from one meter to another and age dates from one millimeter to another depending on the crystals and degree of melting.

We do not know where this rock came from. They do not know. In any case the Martian surface they now explore is a highly altered "new surface" a few million to 1 or 2 billion years old, not a 4.5 billion year old pristine surface of an asteroid. We cannot compare the NOW surface chemistry of Mars with the chemistry of a meteorite fro who knows where.

It could have come from our Earth, our moon, our other planets or their moons, our asteroid belt or any one of the unseen Kuiper belt bodies.

We also do no have bubbles of gas in vesicles in rock to date from Mars as we have no definitive samples from Mars or any where else.

Chris Landau (geologist) November 22, 2013

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