Monday, August 24, 2009

The pet scientist writes another letter to her school

The following paragraphs were written in reply to the teacher at the primary school in Tasmania, Australia with whom I am long-distance partnered as a “Scientist in the School”. He suggested that I “email the students a paragraph on what you are doing in Europe”, because such a letter “can be used to generate questions from the class”. I made my reply as brief as I could manage, but it still turned out to be a full letter, rather than the requested “paragraph”.

My career as a scientist is in the process of undergoing a major transformation. I just spent the past four years working out the pressure and temperature at which Tasmanian Metamorphic rocks formed based upon the compositions of the minerals in the rocks. I did this by comparing them with the compositions of minerals formed during experiments other scientists have done. Now, instead of comparing real rocks with someone else's experiments, I shall perform my own experiments, so that others may compare their rocks with my results. To do this I have moved to Europe, where I have joined a team of scientists who do experiments.

The experiments we do require very special equipment and lots of time. First we take a powder of known composition, and then we seal it in tiny (about 3 mm wide) gold or platinum capsules. We then encase the capsules in a series of slightly larger containers, each layer chosen for specific reasons. Once we've got them all bundled up inside all of the special layers we put them into a special press, which then puts a large amount of pressure and heat on the package. We choose a temperature and pressure which is within the range at which real rocks are metamorphosed underground, and we leave it at that pressure and temperature for a few weeks. (My experiments will run at ~600-700 degrees C and 20,000 to 30,000 bars of pressure.)

During this time tiny minerals start to grow inside the capsules, just as they do in real rocks which are subjected to such extreme conditions of temperature and pressure. After they've been "cooked" long enough, we open up the package, remove and cut open the capsule, and polish the rock surface inside (it is now a rock instead of a powder because the minerals have grown from the powder, and they interlock together just as a real metamorphic rock does). Once it is polished we use a special machine called an Electron Microprobe, which allows us to analyze the composition of the minerals. It takes several hours of hard work to determine which minerals are now present inside the capsule, and what their compositions are.

Over the course of the next year I will repeat the experiment several times, each time using the same starting composition, but different pressures and temperatures. After each "run" I will make notes of which minerals, and what compositions of minerals are present in each capsule, and at what temperature and pressure they grew.

Once I have enough data from a variety of different "runs", I will draw graphs that show the patterns: the relationship between which minerals are present at different temperatures and pressures, and how the compositions of those minerals change as well. Then, other scientists, at other universities, can use those graphs to compare with their real rocks, and try to work out at which temperature and pressure their rocks must have grown.

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