(This interview originally published in the BTA January 2016 Members’ Newsletter.)
Science progresses because people ask questions; it’s not simply about accepting a popular orthodoxy. To ask questions, you must be curious. To answer questions you must be determined and willing to formulate a reasonable hypothesis and then run experiments to test it. Dr. Laurence Garvie, research professor and curator at ASU’s Center for Meteorite Studies, is a good example of what it means to be a scientist. As we walked through the desert adjacent to BTA, which was scorched by a fire five years ago (the Picket Fire, May 2011), Garvie pointed out the new growth on cacti that had been badly burned. One saguaro had put out at least 20” of new growth, and a barrel cactus had grown almost a foot in height. We wondered if this growth spurt was produced by the shock of having been burned, if it was accelerated by the nutrient-rich ash that had washed into the soil, creating fertilizer, or if this was just the normal growth rate of the plants. Particularly intriguing was the unusual fire adaptation shown by the hedgehog cactus, something Dr. Garvie had been following since the start of the fire. Dr. Garvie had a question about nearly everything we saw. For him, every rock, every plant had a story to tell about the complex relationships between minerals and living organisms.
Q: Did your interest in science start when you were young?
A: Yes. My parents used to take me out fossil hunting almost every weekend. My father worked for NASA in Texas, and during the weekends we would look for tertiary Mollusca – shells. I was also captivated by the diversity of microorganisms in pond water. I still have my notebooks from when I was 12. In one set of experiments I tested whether the freshwater hydra would grow back the same number of arms after the body was cut in half. These are fascinating organisms as do not age or die of old age. When was accepted at the University of London, I wasn’t sure what I was going to study. So the University gave me three choices: earth sciences, nuclear engineering, or virology. I picked earth sciences and eventually got a PhD in clay mineralogy. I never wavered from science.
Q: Since mineralogy is your expertise, what would you tell someone who has little interest in chemistry and minerals?
A: I would have people understand that much of the world around them, whether the natural or the man-made, derives from minerals in one form or another. We even contain minerals in our bones and teeth. I was speaking to a classroom of children about minerals. They loved seeing the sulfur because it’s bright yellow and smells peculiar and they also loved pretty quartz crystals. But then I talked about why minerals are important and used an incandescent light bulb as an example. I explained that the glass is quartz sand from a beach or a quarry, the tungsten in the wire from minerals in China, and the metal around the base is aluminum from bauxite mined in Australia. So here in this one product you have more than half a dozen minerals mined from around the world. And each of those minerals has its own story about how it was formed. That was how I tried to encourage the kids to look around, ask questions, and not take things for granted.
Q: You also study meteorites. What is the average size of a “shooting star”?
A: The vast majority of the 45 thousand tons of material that rains down on the Earth from space every year is sand-sized or smaller. When you see a typical fast shooting star, it’s tiny and burning up about 60 miles above the surface of the earth.
Q: How does such a small grain produce such a bright trail?
A: Through incandescence. The meteor hits the Earth’s atmosphere at high velocity – at up to 160,000 mph, producing “ram” pressure – the pressure increase heats the air which in turn heats the meteor almost instantaneously to around 8000° F. If the shooting star were as big as, say, a grapefruit, it would create an impressively huge fireball. Even though my main job is with meteorites and mineralogy, I am also fortunate to have the desert wilderness at my doorstep. To me this wilderness is a research lab waiting to be explored. In the desert it’s often the little things that catch my attention, like a lichen growing in (not on) a rock, or questions surrounding the formation and mineralogy of desert varnish, or I ask myself what controls a particular vegetation pattern.
Q: And that brings us to your interest in the crystals produced by desert plants.
A: I had been in Arizona for about a year and was hiking in mountains south of Phoenix when I found a dead saguaro with pumice-like material between the exposed ribs. I had no idea what that stuff was. Naturally, as a mineralogist, I took some of it back to the lab and x-rayed it and was astonished to discover that it was primarily monohydrocalcite – this was not a mineral I was familiar with or expecting to find. A little bit of research showed the rarity of this mineral. So what followed was several years of research about what happens when cacti die and decay. Turns out that the calcium in the plants can be mineralized through the action of microorganisms and the decay process. A large saguaro contains over 200 pounds of the biomineral calcium oxalate together with many pounds of calcium bonded with the organic material. So when the saguaro dies, something, of course, happens to all of that calcium. Turns out it transforms to monohydrocalcite. A rotting saguaro is a fantastic seething mass of life, and all of that life transforms the elements originally trapped in the living plant into minerals. A whole suite of minerals form in the rotting interior, with different ones forming as the rot progresses. Nesquehonite, which is a hydrated magnesium carbonate, was one of the minerals I identified, together with a magnesium oxalate called “glushinskite” – a wonderful name. These minerals can’t typically survive in a desert environment (it’s too hot – they will dehydrate), but instead form in cavities in the rotting saguaro. If you think of a geode, and how crystals can grow inside its hollow shell usually at high temperatures, well the cavities in rotting saguaros are like wet, smelly, warm geodes!
Q: Have you worked on any other desert projects?
A: Yes. Over the years I had seen images on TV of large areas burnt by wildfires – these scorched lands were covered in white ash. Searching through the scientific literature I found few papers describing the mineralogy of plant ash, especially as a function of plant species. Therefore, the Picket fire provided me with an ideal opportunity to collect ash and determine its mineralogy as a function of plant species. While collecting ash in the still-smoldering mesquite forest along Alamo Canyon west of BTA, I was distracted by an overpowering and pungent chemical odor lingering in the air – but I couldn’t identify its source. As I was walked towards a smoldering mesquite, I noticed at the base of the trunk an orange-sized mass of lustrous needle-like crystals – this was definitely not something I expected to find amongst the ash. It was when I bent over to photograph and collect the crystals that I realized they were the source of the chemical odor. I had never seen anything like this in the desert and was worried that they might be air sensitive and disintegrate in a few hours. I collected the mass of crystals and rushed back to the lab to x-ray it. Despite high-quality x-ray data, I was unable to identify the crystals. However, I determined that it was soluble in organic liquids, which suggested to me that it was an organic compound. I was keen to know if there were more deposits of this crystal and immediately returned to the burnt forest – fortunately many of the large burnt mesquites contained surfaces covered in the crystals. This finding led to one of the most interesting studies that I have been involved in and posed a number of questions that I needed to find answers to: What were these crystals? Where did they come from? How did they form? Was the fire responsible for their creation? Were they stable? How poisonous were they? First I needed to locate the source of the organic compound. To this end I sectioned a fallen 10” diameter mesquite log, hollowed out at one end by fire and containing the pungent crystals at the burnt end, until unburnt wood was encountered. This wood showed a core of pale yellow and porous decayed heartwood surrounded by dense brownish red, fresh heartwood. The decayed heartwood also possessed the pungent odor of the lustrous crystals – so now I knew where the crystals were coming from. But, I wanted to know if the organic material in the heart rot could be liberated by heat. So I took a big lump of the heart rot back home and smoldered it in a barbecue grill, with a foil hat over the chimney to hopefully capture any crystallizing material. After an hour I carefully opened the foil chimney and saw the interior covered with the lustrous smelly crystals! So now I realized that all the fire was doing was vaporizing the organic compound in the heart rot and redistributing it as a solid onto a cooler surface. However, I still didn’t know what the organic material was or how it formed, but the presence of heart rot suggested a fungus was involved. I researched mesquite heart rot, and found that it is commonly caused by a bracket fungus. So, back to Alamo Canyon, this time to search for bracket fungi. After several hours of peering around the bases of mesquite trees (which is not easy in the thick undergrowth along Alamo Canyon) I found my first hoof-shaped bracket fungus – once I saw the first one, I started finding more. Was this the fungus responsible for the chemical smell? Cutting into the fungus I was immediately hit by the same chemical smell – I had found the culprit. In the lab, I put several pieces of the fungus into an organic liquid, and waited to see what crystals would form once the liquid evaporated. Sure enough, lustrous, smelly needles crystallized. The mystery was beginning to come together, however, several important questions still remained: what was this fungus, what were the crystals, and why mesquite? Fortunately, I was able to partner with mycologist Dr. Jessie Glaeser (US Forest Service) – to identify the fungus – Phellinus badius: this turns out to be a widespread species. There was still the question of the identity of the crystals. Dr. Thomas Groy solved the structure – I remember our first meeting when he revealed the structure as a chlorine-rich organic compound (its name is wonderful – tetrachloro 1,4-dimethoxy benzene). Where did all the chlorine come from? I must admit my initial surprise and skepticism. Again, I went back to the literature to see if there was something special about mesquite wood – is it unusually chlorine rich? Surprisingly, I could not find any published literature on chlorine content of mesquites. So, now I had to measure the elemental composition of the wood. Fortunately, ASU houses a linear particle accelerator, which allowed me, with the help of Dr. Barry Wilkens, to probe the chemistry of mesquite wood, using a technique called PIXE (particle-induced x-ray emission). And yes, this wood contains high concentrations of chlorine, roughly 10 times that of other wood. The pieces of the puzzle were coming together – we know what the smelly crystal is, what forms it, and why mesquite trees. However, the significance of this discovery really needs to be explored in a more systematic way. Why is this study important? Most of us have heard of chlorine-rich organic pollutants produced as by-products of industrial processes, and many of these compounds are toxic (anyone remember DDT or dioxins?). But, here we have a potentially toxic natural chloro-organic compound that can be produced in large quantities through fungal decay of wood. Nature is producing a chlorine-rich organic pollutant! Without a doubt, this was the most interesting science project I have been involved in because it led me into fields that I knew absolutely nothing about. Despite the revealing discoveries, many more questions were posed than answered. This project, as well as the one on cactus decay, revolves around the same issue – element cycling in the environment. The plants are taking elements out of the ground (such as calcium, magnesium, and chlorine), and storing them temporarily above ground in the plant. After the plants’ death, these elements are released back into the environment, but often in different chemical forms than they were taken up as.
Q: What have these desert studies got to do with your work on meteorites?
A: At first glance, there may not appear to be a link, but in fact they both tell us about element cycling, but at vastly different time and spatial scales. Meteorites are stardust, and provide insights into element cycling in stars on billion-year time scales, whereas plant growth and decay cycles elements on the Earth’s surface but on time scales of only a few years. In the end, our Earth will be engulfed by our expanding Sun when it becomes a red giant, at which time a new phase of element cycling will take place.
(Check out an hour-long lecture given by Dr. Garvie called The Camp Verde Meteorite. It’s on YouTube and well worth your time.)