This post is written by Salik Rosing. Salik has a PhD in Geology with a focus on computer models of ancient ocean circulation from the University of Copenhagen’s Department of Geoscience and Natural Resources Management. He is currently a postdoctoral researcher at the GLOBE Institute, also at the University of Copenhagen, studying early life on Earth. He believes that sharing knowledge is the most important part of being a scientist, and spends a lot of time writing and talking about his research and science in general. He lives in Copenhagen with his wife and daughter. Follow him on Twitter to find out more about his work.
In my first year as a PhD student at the University of Copenhagen, I got a chance to go to a remote part of Nevada to do fieldwork for 10 days. My colleague needed some samples for her PhD, but she was busy in the lab and couldn’t go. This fieldwork was not related to my own project, which I was quite busy with, but having spent months at my desk building computer models, I was eager to get out in the field again, so I jumped at the opportunity.
~450 million years ago, in what we call the
Ordovician period, a shallow sea covered Nevada and Utah. In this sea, a
diverse and vibrant community of animals thrived in the warm waters of a planet
that was much warmer than today. However, this warm and diverse world would
soon start to cool down into an ice age, and the second largest mass extinction
in Earth’s history would reduce the diversity of animals in the oceans by half.
As geologists, we are interested in understanding what caused this mass extinction. There are many ideas, but it seems that oxygen levels in the oceans may have played a role. To study this, my colleague had tried to do some chemical analyses on rock samples she had collected at an outcrop close to Vinini Creek in central Nevada.
In the Ordovician, these rocks were mud on the seafloor, but have since been buried and squeezed into solid rock. The minerals in the rock can give us an idea about the conditions on the seafloor when the rocks were still mud.
What she found was that sulfides – a group of minerals that are unstable when oxygen is present – were rare in her samples. This suggested that there had been plenty of oxygen at the seafloor. However, she also realized that since the rocks had been sampled directly from the surface of the outcrops, they had been exposed to the atmosphere and its oxygen, and it is possible that any sulfides that may have been in the rock would have reacted with the atmosphere and dissolved – we call this process weathering. If the surface rocks were weathered, their chemistry would not reflect oxygen in the ancient oceans, but the oxygen present in the atmosphere today!
She needed to get rock samples from below the surface – hence, my trip to Nevada. Rocks below the surface would have been isolated from the environment since they were deposited as mud on the seafloor, and so we could expect that their chemistry would actually reflect the environment in the Ordovician oceans. To get to these rocks, we use a handheld drill.
Drilling is hard work. One person keeps the equipment steady and pressed down against the rock for up to an hour at a time, while the other pumps water down the hole to cool down the drill bit. This continues through several meters of solid rock, 30 cm at a time. The samples are retrieved from the hole, wrapped in tinfoil and labeled. We only broke for lunch and for our daily trip to town to fill our 10-gallon jugs with water for cooling. As we drove, we would see big eared mule deer jumping across the road. In the distance, the snowcapped mountains and the cloudy autumn sky.
In the evenings, we returned to our camp by a creek in a grove of cottonwood with yellow autumnal leaves. We were so far from everything that there was no artificial light, and we could see the stars overhead as we ate our dinner cooked on a small camping stove, then crept into our tents with lots of warm clothes and slept through the cold desert nights.
On the fourth morning I woke up early. Big snowflakes where blowing through camp and had already covered the ground. If we didn’t leave quickly we wouldn’t be able to drive on the dirt road and could be stuck for days. So we packed, got in the car and drove to nearby Eureka – a small former mining town which describes itself as the friendliest town on the loneliest road in America – where we would end up spending five days in a motel waiting for the weather to clear up so we could continue our work. We had our meals in the hotel bar, decked out in Halloween decorations, where we talked to locals and to people passing through. We went on walks through the snowy streets, and otherwise read and listened to music.
On our last day in Nevada, the weather was sunny. We drove through the snowy landscape to the outcrop, drilled one more meter and drove back to Salt Lake City where we caught a plane back to Denmark.
My colleague got her samples and finished her PhD. The unweathered rock did show signs of low oxygen level before the mass extinction.
I had spent a good chunk of my time on a trip that I couldn’t directly use for my own project, but I had gotten something much more important out of it. I got a break from my desk. I got to rediscover the fieldwork that drew me to become a geologist in the first place. I got the memory of a tent by a creek in autumn with yellow cottonwoods, mule deer on the road and the Milky Way above. And every time I see a Halloween decoration, I think of my time in the friendliest town on the loneliest road in America. Even if I did end up slightly busier at the end of my PhD, it was a small price to pay for those memories.