From Mars to Earth in 1 easy step.


This is a piece of Mars, the planet.  It came to me via a meteorite, Dar Al Gani 476, some 60,000 years after it plopped itself down in the Libyan Sahara, to later be discovered on May 1, 1998.  This particular piece is about the size of your thumbnail, assuming you’re not some kinda freak with abnormally sized thumbnails.  It weighs in at a hefty .240 grams.

Dar Al Gani 476 a meteorite known to be from Mars

Dar Al Gani 476 a meteorite known to be from Mars

It was evicted from Mars with significant force some 1.1 million years ago, as a completely different, and much larger meteorite slammed into Mars with enough force to blast chunks of the planet clear into space, out of Mars’ orbit, and into orbit around the Sun, where they chilled out for a while, until a few of them eventually ran smack into Earth. DAG 476 was the 13th meteorite from Mars to be found, giving it the nickname “Lucky 13”.  It was the first to be found after ALH84001 was made famous in all that brouhaha about whether or not it contained traces of life, which unfortunately, it probably doesn’t.

DAG 476 is an achondrite, belonging to a class of meteorites known as the SNC group, which stands for Shergottites, Nakhlites, Chassignites, of which all members originate from Mars.  DAG 476 is of the Shergottite variety, which got its name from the Shergotty fall in 1865 in India.  It’s the most common sub-group of martian meteorites, having characteristics which suggest they solidified at, or near the surface of Mars out of magma from deep beneath the surface.  They don’t all come from the same place on Mars though, which means this has happened many times.  The composition of DAG 476 matches up perfectly with 4 other martian meteorites, DAG 489, DAG 670, DAG 735 and DAG 836, suggesting that all five were probably from the same body that broke up upon entry into our atmosphere.  There are about 30 different distinct meteorites known to be from Mars in total, if you count the multiples as one.  As a consequence of lying there on Earth for 60,000 years, the original fusion crust generated on entry into the atmosphere has long since eroded away, with veins of carbonate running through the occasional crack due to weathering.  I think those are the light greyish parts at the top, running down the left side, but I’m pulling that straight out of my ass, without any confidence whatsoever.

It’s kind of astonishing how much Science can tell us about this rock.  It crystallized originally to form a rock about 474 million years ago, which is actually quite young, by meteoritic standards, just a meter or two below the surface of Mars.  They can tell how deep it was buried by the rate at which it cooled, which affects the crystallization process.  There are shock features within, that point to it experiencing enormous shock, as it was blasted free of its homeworld, into space.  Incidentally, the age of 474 million years would also imply that there was volcanic activity on Mars less than half a billion years ago.  Geologically speaking, that’s pretty recent.  The alignment of the olivine, and pyroxene crystals within it indicate that it formed in an extruded lava flow.  I guess that means they’re stretched in one direction.  If Mars was geologically active 474 million years ago, there’s probably at least *some* activity today.  Perhaps not full fledged eruptions with lava flows, but it’s fairly likely that there is something.   When it was floating around in space, it was being bombarded by high energy cosmic rays, which are capable of smashing the atoms they collide with into smithereens, or being absorbed by them, turning into new, radioactive elements, like Helium-3, and Argon-38.  By measuring the relative quantities of these gasses, it can be determined how long it was in space.  When this rock landed on Earth, Man was just getting the knack of making stone tools.

The other side of Dar Al Gani 476, known to be from Mars

The other side of Dar Al Gani 476, known to be from Mars

How do we know it’s from Mars?  Well, back in the 1970s, one of the things the Viking landers did was sample the atmosphere on Mars, characterizing the relative abundances of gasses in the air.  It also sampled the soil, to determine the chemistry.  Inside this meteorite are wee little microscopic bubbles of trapped gasses that have been locked up in there ever since this rock formed, trapped inside of crystal cages.  Wouldn’t you know it, when sampled, those bubbles turn out to have the exact same proportion of gasses as the Martian atmosphere did, when measured by the Viking landers.  The composition of the rock itself is very similar to the composition of rocks on Mars.  In a neat scientific coincidence, one of the Mars meteorites, known as EETA79001, discovered in Antarctica in 1979, was found to be highly similar in composition to a rock nicknamed “Bounce” that was studied on Mars, by the Opportunity Rover.  The data seems to indicate that Bounce itself is from elsewhere on Mars.  It was also ejected in an impact, but not with enough energy to get launched into orbit around the Sun.  It’s conceivable that Bounce is even from the same event as EETA79001, it’s at least likely to be from the same place on Mars.  What are the odds of finding pieces ejected from the *same* meteorite impact on two different planets?  It boggles the mind.

This is my single most treasured possession.   What could possibly beat a piece of another planet?    I can point to it in the sky, and say “Yup, I’ve got a piece of that.”  It’s tens of millions of miles away, and it’s on my bookshelf.  It’s the only place in this solar system where we can seriously see ourselves living one day, in our craziest dreams and hilariously bad movies, perhaps not even in bubbles, or space suits.  It’s the only place remotely similar to Earth.  And it was generous enough to send a souvenier all the way here, to inspire us to dream big, so that one day, if we’re good little human beings, and we don’t kill ourselves first, we can go to Mars, and steal all that precious, precious land.  The best part?  There aren’t even any natives to oppress/subjugate/relocate/eliminate!  No guilt, and we get all the casinos to ourselves!

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From marbles to meteorites


Ok, so, meteorites. I’m gonna do a post with multiple items this time, because I’m trying to make a kickass point. In general, there are several different general types of meteorite. They are either stony (chondrites), iron (iron), a mix of iron and rock(stony/iron, including pallasites), or a funky 4th category(carbonaceous chondrites) that are crazy carbon rich. I’ve got a few meteorites, but not all the ones I want. I’m gonna include some pictures from things I don’t have yet, just to demonstrate my overall point, and to show why I must own them.

Now as we all know, the Earth’s interior is differentiated into different layers, with different properties. We have the rocky outer crust, where we live, which is ridiculously thin, between 2 and 30 miles thick or so. Considering the Earth is about 8000 miles in diameter, that’s pretty damned thin. Next, we have the still rocky, but now fluid mantle. Here the pressure and temperature has melted the rock and turned it into a sort of super-sticky fluid. The mantle can be further subdivided into an upper/lower, but that’s not really relevant, so I’ll just say the mantle is about 1800 miles thick. Beneath that we have the outer and the inner core, both consisting primarily of iron and nickel. Almost everyone knows about the iron, but most people don’t know there’s quite a bit of nickel too. Why, you might ask?

Well, back in the olden days, before the Earth, or the Sun existed, a really big star blew up somewhere pretty near to the cloud of gas that was eventually to be our solar system. This star blew up because it had started fusing iron in it’s core, and for stars, this is the end of the road. Fusing iron doesn’t produce energy, it consumes it. It starts sucking energy out of everything around it, and the outward radiation pressure drops. Gravity starts to win. But the star does not go quietly. As it simultaneously implodes, and explodes, its core becomes a black hole, while the rest of its innards, get ejected at a significant fraction of the speed of light in the kind of explosion that’s visible across the Universe. In the process, pretty much every chemical element from iron on up in the periodic table is created, all within a few seconds. That’s where uranium is made. That’s where gold is made.

Eventually the shockwave, followed later by the ejected bits collide with a gas cloud, and cause a part of it to collapse, just like blowing into a cloud of smoke. Now, the important thing, is that these supernova explosions are very rich in a particular isotope of iron called Iron-60. Iron-60 is radioactive, and it decays into…Nickel-60! This is where all that nickel came from. So, when you’re looking at an iron meteorite, you’re looking at the pieces of a dead star. The ratio of iron to nickel tells you something about the neighbors during the period when it formed. It tells you something about the stars that gave birth to it. When that meteorite formed, it was probably mostly iron. Over time, the radioactive Iron-60 in it decayed and turned into very stable Nickel-60, where it has remained ever since.

So, then some shit happened, a star formed, and along with it, a bunch of planets. Some of those planets are still with us today. Others, well…they didn’t make it. Our solar system was one crazy place back then, with a whole lotta shit flying around in a whole lotta directions, colliding, accreting, etc. Point is, planets are being assembled. Violently. Sometimes they get disassembled by accident. And that’s how meteoroids are born!

Korra Korrabes meteorite from Namibia

This is a stony meteorite, technically known as a chondrite. There are many different varieties of these, just like there are many different varieties of rock on Earth. This particular one is an “H3 Chondrite” named Korra Korrabes (after where it was found). It’s a breccia, which basically means it’s composed of loose gravel filled with finer dirt, and then compacted. It’s a bit like a natural concrete, I guess. This one came to earth in Namibia, and was later discovered in 1996 in a dry river bed by a farmer. It is a piece of the crust/mantle of a planet that’s no longer with us.

A piece of the Sikhote-Alin fall

A piece of the Sikhote-Alin fall

This is an iron/nickel meteorite. It’s from Sikhote-Alin, which is a mountain range in Siberia. It’s technically classified as “coarsest octahedrite”, which refers to the crystalline structure of the metal it’s composed of. The dimples in the surface are called regmaglypts, and they’re basically the result of air pressure on the molten outer surface of the meteorite after it meets the atmosphere and heats up. It’s a lot like what would happen if you pursed your lips and blew really hard into a bowl of ice cream. If you cut it open(the meteorite, not the ice cream,) it would look something like this.

Toluca-IAB iron meteorite w/widmanstatten pattern

Toluca-IAB iron meteorite w/widmanstatten pattern

It’s called a “Widmanstatten Pattern” and it is unique to iron/nickel meteorites. It can only be created when a molten chunk of iron/nickel floating in zero gravity under a near perfect vacuum, is allowed to cool veeeerrrry slowly over millions of years, giving these amazing crystals time to form. The bands basically represent different nickel/iron alloys. Because the ratio of iron:nickel is different between the stripes, the crystal structures they form are slightly different. This manifests itself as a series of criss-crossing lines throughout the body of the meteorite. This particular one is from the Toluca, Mexico meteorite. When it was found, in 1776, the locals were turning chunks of it into farm equipment, cuz, hey, free iron! Its constituent atoms were born in an ancient star that went supernova. It got its shit together, and became the core of a planet that’s no longer with us. It died in its youth, victim of a driveby planet. RIP, little meteor. RIP.

Imilac Pallasite

Imilac Pallasite

This is a pallasite. These things are fucking beautiful, and I MUST own one. It’s strange, it’s got a whole crapload of iron, but it’s not pure iron/nickel like the other ones. Why? Well, I’ll tell you. That’s the boundary between the mantle, and the core of a planet that’s no longer with us. Why is it all gemstoney? Well, that’s how gemstones are made. Immense heat + immense pressure + a stocking full of coal = diamonds. In this case, it’s Olivine, also known as Peridot. Are you born in August? How’s that for a birthstone to make your friends jealous?

Each of these things is older than any rock, anywhere on Earth. They’re all about 4.5 billion years old, a bit older than the Earth itself. They’re the shattered remains of planets that just didn’t quite make it. They survived long enough to differentiate into an iron core, with a rocky outer crust, and that incredible boundary layer. They just couldn’t quite hang in there for the long haul though. Those early few hundred million years were pretty hazardous. Imagine how hazardous it has to be for an object the size of a planet to be routinely obliterated? It’s like that.

Flash back to Starwars, Vader is destroying himself some homeworlds just to make the princess cry, cuz he’s hard like that. Remember that planet exploding? This is like that. Only for real. And on a massive scale, like “OH FUCK, LOOK OUT! HERE COMES A PLANET!” If you find yourself in such a situation, it’s probably best that you grab your ankles, and think of England.

When you look up at the moon, and you see these giant scars, those were some pretty massive bodies smashing into it at pretty incredible velocities. It was such an impact that created our moon in the first place, when one of those mars-sized erstwhile planet wannabes picked a fight with the erstwhile planet wannabe Earth, and lost. The impact was sorta oblique, so it happened to fling big chunks of both bodies into orbit around the new Earth + 1. Those chunky bits coalesced into our Moon.

Oh, the 4th category, Carbonaceous Chondrites? Those are basically comets. They formed in the outer solar system, around Pluto’s neighborhood. They’re chock full of water and carbon, just the kind of thing a growing planet needs to establish a biosphere. The Tagish Lake meteorite is an excellent example of a carbonaceous chondrite.

Ok, so anyway, my point. Science rules, Natural Selection doesn’t just apply to monkeys and Creationists, and meteorites aren’t just rocks from space. They tell you something about where you came from, and where they came from, where the Earth, and the Sun themselves came from. Every time I think about what these represent, it puts me into a state of awe that words just can’t convey. And yet, it’s just a rock, or just a lump of metal. Hell, I bet you could make some damned fine farm equipment out of it.

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