Fieldwork in the Atacama Desert, Chile

Friday, 28 September 2012

To boldly do geology where no man has done geology before

So it’s been a while since my last post as the university has been pretty quiet over the summer and it’s been a good time to get my head down and crack on with some serious sciencing without the disruption thousands of undergraduates bring. However, after seeing this morning that the Curiosity Rover had been doing some sedimentology on Mars,, I couldn’t help but get a little bit overexcited. Doing geology in space must be every lithophile’s (see one of my previous posts) dream job and so here’s a post of my ramblings and ill-informed opinions on Curiosity and space geology and why it’s the best thing ever (and also why I hate it).

This morning’s news report on Martian conglomerates (hereand here) is some serious proof that a significant amount of flowing water must have been present at some point on the surface of Mars. Very poorly sorted (i.e. those with a wide array of particle sizes) conglomerates with sub-angular to well-rounded clasts, as can be clearly seen in the photos, can only be formed by deposition from (relatively) fast flowing water. Wind transport, which does occur due to the high Martian winds (see here) and also creates well rounded clasts, generally creates a well sorted deposit such as an aeolian sandstone as smaller particles are winnowed away and larger pebbles don’t roll so far.  A poorly sorted deposit could have been formed by some sort of terrestrial gravity flow, a slump or a slide, however, this would produce a breccia with highly angular clasts as these terrestrial flows do not travel a great enough distance for transportation processes to erode the particles enough.

Curiosity's photo shows Martian conglomerates look just like Earth ones

The calculation that "From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep," [Curiosity science co-investigator William Dietrich of the University of California, Berkeley] put me straight back to undergraduate sedimentology lectures and the Hjulstrom Curve. 

Hjustrom Curve
This graph (see above image) is a well-used tool by sedimentologists studying fluvial transport processes in Earth systems to allow the back-calculation of the velocity of water flow that deposited the sediment by showing what size material will be entrained, transported and deposited by different velocities of flow. From both the description of this shallow, fast moving stream and looking at the deposits I’m put in mind of braided river channels in upland areas arid areas like this (but without the shrubs):

Braided river system (image from

Now for a little rant, but first I’ll put this all in context with my work. I work on high resolution geochemical analysis of fossil corals and half of what I have been trying to do for the last 12 months is high resolution trace elemental analysis. For this I stick my coral stem into a machine called a laser-ablation-inductively-coupled-mass-spectrometer (LA-ICP-MS for short), which is a room-sized, very expensive, serious piece of kit. In short, this machine uses a laser to vaporise the carbonate, this  vapour is entrained into a gas which is superheated to around 10,000K and ionised to form a plasma which then goes into a mass spectrometer where the proportions of ions of various elements that make up the sample are analysed. This is done along a tract of the coral wall, producing over 3000 readings for a sample less than 50mm long and should, in theory, let me see seasonal changes in trace element composition allowing me to investigate growth conditions (see this paper where they've managed to do it on modern samples). I say ‘in theory’ as I have yet to get any meaningful data from this technique, all I have produced are noisy squiggles of data which cannot be calibrated to any quantitative figures. So while I can see what elements are present, I have no idea of the proportions they are in, and thus cannot draw any conclusions, and I have no real idea why.

Now, with that in mind, you may see why Curiosity annoys me. This little robot travels over 120 million miles through space, successfully lands on another planet, drives around a landscape no human (and very likely nothing else) has ever set foot on, and finds a rock (named ‘Coronation’). All in all a very impressive feat of human engineering which we should all be proud of. But then it, and for obvious reasons this is what I can’t deal with, it fires a laser at the rock, ablating it and producing an ionised plasma in the exact same way I do here, and using it’s ChemCam spectrometer it analyses the elemental content (shown below) of said rock from the produced light spectra of the ions in the plasma, and discovers it to have the composition of a bog-standard lump of basalt (details here). Ok, so the rover may be analysing at a lower resolution and using light rather than mass spectrography, but still, how can it get real, meaningful results in space, at a distance, outside the laboratory, in a non-vacuum, uncontrolled environment, using a machine maybe a hundredth of the size of mine, when I can’t???

Unfortunately, the answer is funding and expertise, things NASA has a hell of a lot more than I do for my research (even with the generosity of NERC and UEA). So, as I can’t do anything about this I’ll end this rant with a plea; please NASA, let me be a space geologist too (as if you can’t beat them, join them).

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