Summer Rocks
Hello all! I’m writing to you from Cambridge, Mass – my fabulous home for the summer. The KINSC awarded me a travel research grant to work for Dr. David Johnston of Harvard University’s Earth and Planetary Sciences Department. I’m about half way through my ten weeks here and already wishing for more time.
On a general scale, the Johnston Group is trying to characterize the marine and atmospheric environments of 4 to 6 hundred million years ago. This time period corresponds to the end of the second snowball earth episode, when the entire Earth might have been covered in ice, and the beginning of complex animal life on Earth. We want to know what conditions might have made the latter possible. Our clues lie in the carbon, sulfur and iron contents of rock samples that, while underwater at the time, now lie in the mountains of Mongolia and Canada.
We work with shale and carbonates, but right now I am focusing on the carbonate samples.
When the rocks come to the lab from the field, they first have to be CRUSHED in a shatterbox. I load the rocks into the metal disk, clamp the unit down carefully, and press go! The machine does its thing and turns solid rock into powder.
In the wet lab, the samples are mixed with hydrochloric acid to dissolves the inorganic carbon they contain. They fizz quite a bit as they release carbon dioxide and more acid is added until they no longer bubble and the pH remains low overnight.
I then use a vacuum to filter out the clay-like residue. The yield is so small on this set that I am having trouble scraping the leftover residue from the filter paper without introducing more organic material, so I am going to try a centrifuge-based procedure next week.
The next stop for these samples is the mass-spectrometer. I load about 4 mg of rock powder into a tiny tin cup – think a 3mm wide cupcake holder – and roll it into a tiny ball with tweezers. These can be loaded into the instrument and analyzed for organic carbon content after a bit of excel magic.
There’s a lot of work, but I’m not doing it all alone! Along with Dave, I spend the day with Andy, our incredibly helpful lab manager, and Esther, another undergrad working for the summer.
In no particular order: Tie dying my lab coat, listening to NPR, seeing Helen and Sarah Choyke, sitting in on reading/discussion groups, biking to work, building and painting a table for the lab, using the label maker... and much more!