If you like outdoor adventures, you might love to be a geochemist.
Geochemists are both geologists and chemists. As geologists, they study the world around them by observing rocks. As chemists, they examine the compounds and elements that things are made of. Geochemists use the compositions of rocks (or fluids, or gases) to understand how Earth systems (such as volcanism or the climate) work now or how they worked in the past.
As a geochemist, I study the history of Antarctic glaciers by analyzing rock samples from the Dry Valleys of Antarctica.
The Dry Valleys region is a cold desert, so dry that it doesn’t get enough snow to be covered with ice. Have the Dry Valleys always been ice-free, or were they ever covered by ice sheets? Scientists need to understand how the Antarctic ice sheets behaved in the past in order to accurately predict how they will react to global warming. Geochemists are detectives who can decode the clues hidden within the region’s rocks, by measuring isotopes.
Isotopes, such as neon-20 and neon-21, are variations of the same chemical element with different masses. When a rock is exposed, high energy particles from outer space (cosmic radiation) produce special isotopes (cosmogenic nuclides) in the rock. Some (such as neon-21) are stable and always stay in the rock grain in which they are produced. Others (such as beryllium-10) are unstable and radioactively decay over time. A rock covered by thick ice is shielded from cosmic radiation and no new cosmogenic nuclides are produced. Beneath the ice, the number of stable nuclides stays the same, but the number of unstable nuclides goes down as they decay. The proportions of cosmogenic nuclides in a rock reveal whether it was ever covered by a glacier. With enough rock samples, we can find out what an ice sheet looked like millions of years ago.
First, our team needed to go to Antarctica to collect samples (the best part of studying the Earth is that you get to see the world). Because Antarctica is in the southern hemisphere, we did our field work between November and January during the Antarctic summer (otherwise it would be too cold). Just getting to our field site (where we wanted to collect samples) required a long flight in a military plane from New Zealand to McMurdo Station (the major U.S. research station in Antarctica), a short helicopter ride to our campsite in the Dry Valleys, and a short hike to the field site.
Every morning, we woke up in a beautiful landscape all to ourselves. We carried backpacks containing sample collecting gear, extra warm clothes, a thermos of hot water (even in a cold desert we needed to stay hydrated) and plenty of snacks. No flashlights though—the sun never sets during the Antarctic summer!
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At the field site, we sampled the bedrock, not loose rocks such as boulders, which might have been moved from elsewhere. We made sure that the rock could “see” the sky so it had enough cosmogenic nuclides to tell us something about the past. We avoided rocks that were shielded by other rocks. We also wanted rocks made of large grains, because when we analyze them in the lab, we pick the grains one by one with tweezers, so the bigger the better. Finally, we looked for a vulnerable spot (near an edge or a crack) so that it wouldn’t be too hard to break off a chunk.
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This chunk had to be about the size of a grapefruit. Collecting it usually took a few good whacks with a hammer and a well-placed chisel, but sometimes it took me several minutes of rock abuse before the sample was free. Next, I took the GPS coordinates of the sample location and wrote them, along with the sample name (not Bob, but for example, SR-08-007 for the seventh sample taken in Sessrumnir Valley during the 2008 field season), in my field notebook and on a canvas sample bag. I also wrote down the type of rock, the name of the day’s field site, and the amount of shielding from nearby mountains, cliffs or ridges. I needed to keep track of all of this information to interpret the data we would get from analyzing the sample.
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I took photos of the sample and surroundings to remember all of the details months or years later. Finally, I stuffed the sample into the bag and moved on to collect another sample. At the end of the day, I put all of my samples in my pack to carry all 20-30 pounds back to camp. There, we packed our bagged samples together in wooden boxes to be flown back to McMurdo Station, then shipped to the U.S.
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I took photos of the sample and surroundings to remember all of the details months or years later. Finally, I stuffed the sample into the bag and moved on to collect another sample. At the end of the day, I put all of my samples in my pack to carry all 20-30 pounds back to camp. There, we packed our bagged samples together in wooden boxes to be flown back to McMurdo Station, then shipped to the U.S.
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We needed a lot of samples from many different places to develop a good understanding of what the region was like in the past. We spent a month camping around the Dry Valleys and collecting samples.
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We returned to our lab at Harvard University in January 2009. But our samples didn’t leave Antarctica until February, when the sea ice around McMurdo Station got thin enough for a ship to come pick them up. They didn’t arrive at our lab until April 2009. Even then, we had to prepare each sample before the analysis could begin.
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LAB WORK DETAILS: To prepare each sample, I crushed a piece and separated the grains. Under a microscope, I used tweezers to pick out the grains I wanted: only grains of pure quartz from our sandstone samples, because the cosmogenic nuclides we wanted to measure are produced only in quartz. This step took a few hours for each sample. In time I started to enjoy the simple beauty of clear quartz grains at high magnification.
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Next, I soaked the quartz grains in a strong acid solution to remove contaminants from the outside of each grain (this was the only time in my science career when I actually wore a lab coat). Contaminants mess up measurements, giving us the wrong information about what really happened in the Dry Valleys. After the acid soak, I rinsed the grains with purified water (the acid is a contaminant too!), dried them, weighed them, and wrapped them in niobium foil (like aluminum foil, but stronger and more expensive) before loading them into the machine that measures isotopes (the mass spectrometer).
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* For an overview of geoscientist careers, click on “Listen to the podcast…” at the Sloan Career Cornerstone Center. It’s an introduction to the required schooling, a day-in-the-life of a geoscientist, and jobs.
* For another overview, read "Geoscientist" at ScienceBuddies.org.
* Link to 23 geoscientist profiles including an astrogeologist, a geophysicist, a hydrologist, a micropaleontologist, and an energy policy program manager.
* Watch the video, Careers for Geoscientists, about opportunities to work on the atmosphere, oceans, and the solid-Earth. Interviews reveal adventures and travels, outdoor work, and use of high tech instruments.
* Watch a video of geochemist Andrew Jacobson sharing how his path into geology took him to the Himalayas. The video is long (28 minutes) and a bit slow, but worth the time if you want to get a feel for life as a geology professional or as a college student.
* Watch a video of geochemist Frank Ramos. Beginning at 14 minutes, you can visit his lab and watch student researchers extract the interesting parts of rocks for analysis. Beginning at 20 minutes and especially from 23:30 to 29 minutes, see a simple explanation of how a mass spectrometer works (the same kind of machine that Jenny Middleton uses).
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With the measurements, the mass of the rock grains we put into the machine, and the information we gathered about each sample in the field, we can calculate how much of the cosmogenic nuclides were in each sample and deduce the exposure history of our field site.
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Our results and conclusions will help support or rule out different hypotheses about the past and future of the climate of Antarctica, and help settle current debates among scientists world-wide. So, were the Dry Valleys covered by an ice sheet millions of years ago? If they were covered, when did this happen and for how long? Well, we’re still working on it, but I’ll let you know when I find out.
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ABOUT JENNIFER MIDDLETON
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When Jenny is not working, she loves reading, watching scientifically inaccurate natural disaster movies, and playing outside.
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LINKS
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* Relive Jenny's expedition in Antarctica at her team's blog.
* Read an article about Jenny's mission in Antarctica.
* Read a description of geochemist careers.
* Read an article about Jenny's mission in Antarctica.
* Read a description of geochemist careers.
* For an overview of geoscientist careers, click on “Listen to the podcast…” at the Sloan Career Cornerstone Center. It’s an introduction to the required schooling, a day-in-the-life of a geoscientist, and jobs.
* For another overview, read "Geoscientist" at ScienceBuddies.org.
* Link to 23 geoscientist profiles including an astrogeologist, a geophysicist, a hydrologist, a micropaleontologist, and an energy policy program manager.
* Watch the video, Careers for Geoscientists, about opportunities to work on the atmosphere, oceans, and the solid-Earth. Interviews reveal adventures and travels, outdoor work, and use of high tech instruments.
* Watch a video of geochemist Andrew Jacobson sharing how his path into geology took him to the Himalayas. The video is long (28 minutes) and a bit slow, but worth the time if you want to get a feel for life as a geology professional or as a college student.
* Watch a video of geochemist Frank Ramos. Beginning at 14 minutes, you can visit his lab and watch student researchers extract the interesting parts of rocks for analysis. Beginning at 20 minutes and especially from 23:30 to 29 minutes, see a simple explanation of how a mass spectrometer works (the same kind of machine that Jenny Middleton uses).
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* Read about the fascinating moment when an arts major turned into a geologist.
* Read about world-class expert seismologist Lucy Jones, "the Earthquake Lady" her work and career path, beginning at age eight.
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* Read about world-class expert seismologist Lucy Jones, "the Earthquake Lady" her work and career path, beginning at age eight.
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Updated on January 28, 2012
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