Wednesday, April 25, 2012

Wednesday April 25, 2012: The awful truth about my experiment

Two years ago I placed an array of glass and marble tiles in the desert here to see if they would become colonized on their undersides by cyanobacteria.  My main purpose in returning to Namibia was to check on them.  In the photo below you can see how the array looked in 2010.  There were six rows of ten tiles each:

I was so pleased with the project that I put similar arrays on White Mountain Peak in California, in the arctic, in Arabia, and in the Mojave Desert.  Of these arrays, the only one I have been back to is the one on White Mountain Peak.  A marmot had dug his tunnel right through the array and had stolen some of the tiles.  I had to re-do it.

Yesterday evening I returned to the 2010 Namib array.  The tiles lie flat on the ground about a quarter mile off the road, miles from the nearest humans.  I was the only person on earth who knew their coordinates. 

The array wasn’t exactly as I left it.

I couldn’t believe it.  A burrowing rodent had tunneled right through the array, flipping tiles over, scattering them and burying them.  Some of the glass ones were even broken!  How could that be?  Of the sixty tiles I had left there, I couldn’t even see half of them.

Bad luck?  This was the only rodent burrow in sight.

Slowly the horrifying truth seeped into my shocked, jet-lagged brain.  This was no accident.  It could not be a coincidence that the first two arrays I put in place, on two separate continents, were both disturbed by rodents.  Rodents must be attracted to these arrays.

Maybe they think the glass tiles shine like water.  Maybe they like the human scent.  Maybe something about the geometric, checkerboard-like pattern offends their rodent sensibilities.   But the experiment depended on the idea that, once they are put in place, Mother Nature will treat these tiles just like she would any natural stones.  She doesn’t.  She selects them for special treatment.

It’s a good thing I still have my day job.

And I had just finished putting five more arrays of tiles in the desert here, of twelve tiles each.  Three rows of four.  Will those get vandalized too?  Should I go back and put the tiles farther apart from each other?

Looking more closely at the wreckage of my experiment, it appears that a little bit of data can be salvaged.  A few tiles on the left-hand side of the array are still in position.  Turning over the marble ones, I found sand and small pebbles cemented to the surface of the marble.  This, according to Don Cowan, is due to extra-cellular polysaccharides secreted by bacteria.  In other words, the bacteria produce a kind of glue that binds sand to the stone’s surface.  There was no sign of any green film of cells, though.  Don and Chris McKay think that maybe the production of these polysaccharides is the first step in hypolith colonization.  If so, then it obviously takes a lot longer than two years to make a hypolith.

The glass tiles, in contrast, appeared smooth and clean without anything sticking to them.  Probably too much light gets through them for the bacteria to be comfortable.

All this is very preliminary.  I will return to the site later today to re-analyze it stone by stone.  Don’s group will collect a sample of the polysaccharide- bound sand for genetic analysis.  I still haven’t decided what to do going forward, but I am inclined to leave the mess exactly as it is now.  The wind and rain should even out the dirt pile.  We might still learn something from this array, if we are patient. 

(Update on Friday April 27:  Mary Seely, Director of the Gobabeb Centre, says rodents here like to begin their burrows on a firm, not sandy, surface.  She believes they like the way the array feels hard underfoot.  Maybe in the future I should space the tiles out more.  However, all is not lost.  See my post from April 27 - we still got lots of good samples and data from this experiment, and expect to get more in the years ahead.)

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