Mines News

Release Date Wednesday, October 19, 2022

South Dakota Mines Study Shows Fossil Dissolution Rates

Colleen Sullivan, who authored a newly published paper quantifying fossil erosion, is shown here working in a lab at South Dakota Mines on her research.

Weathering and erosion are constant processes on Earth, and dissolution due to rainwater is one of the primary ways rocks and minerals break down. But paleontologists have not yet gained a complete understanding of the rate fossils erode once they are exposed at the surface. South Dakota Mines graduate student Colleen Sullivan set out to get some answers. Her research has just been published in the peer-reviewed open-access scientific journal PLOS ONE.

“I was doing some undergraduate research looking at how long fossils survive on the surface when exposed to rainfall and there was little quantitative research on the subject,” says Sullivan. “We often saw qualitative speculation on this topic, and there was research done on rates of dissolution for individual minerals. But this is the first time someone has put a numerical value on the rate of fossil dissolution due to interaction with rainfall.”

Sullivan completed her masters in paleontology at Mines in 2022. Her research involved mosasaurs – the giant marine reptiles thrived at the end of the age of dinosaurs in the Western Interior Seaway that covered much of the Great Plains of the United States. Mosasaurs were common in this ancient seaway and today their fossilized bones are relatively abundant. They can often be found protruding from a Cretaceous age rock layer called the Pierre Shale Formation that was deposited at the bottom of the former seaway more than 66 million years ago.

During her research, Sullivan used fossil vertebrae from a late Cretaceous mosasaur. The vertebrae, in the South Dakota Mines Museum of Geology collections, were too fragmented to be museum display quality but were still identifiable as mosasaur fossils. These vertebrae were also collected without detailed location information, so they were less valuable as research specimens.

“We wanted to look specifically at how water interactions impact fossils,” says Sullivan. Previous studies show that rainwater is one of the main causes of erosion and dissolution for several types of minerals. “One of the goals was to determine how water geochemistry impacts the long-term stability of fossils in the field,” says Sarah Keenan, Ph.D., an assistant professor in the Department of Geology and Geological Engineering at Mines. 

The fossil vertebrae were tested to determine the time it would take to dissolve with various levels of acidity that mimic the chemistry of average rainfall. Sullivan tracked the amount of fossil material lost to the solution by testing the specimens before and after dissolution using X-ray diffraction and optical microscopy. The study helped quantify the various minerals lost during the treatments. Her results showed an expected outcome: higher rates of acidity lead to faster dissolution. She then used the data to calculate how long an exposed fossil might stay at the surface before being lost to weathering and erosion.

“If we just focus on rain, the smaller fossils will be dissolved and unrecognizable in about a decade,” says Sullivan. “Something like a skull or larger fossilized bone with more mass is going to vary; bigger fossils could last longer on the surface maybe a century. But for the smaller bits, like individual vertebrae, it could be a 10-year scale.”

The paper not only has implications in helping paleontologists understand how long they have to collect a fossil once it’s exposed at the surface, but it also adds to the understanding of what types of fossils are preserved overall. “This is important for addressing biases in our fossil collections as a whole,” says Keenan.  “Not everything gets fossilized in the first place, and then the limited selection of fossilized remains are exposed and degraded at the surface, further reducing the selection. So, when we are talking about the whole fossil record, we are looking at a snapshot of a snapshot of life on earth.”

Keenan notes that fossils are rare, so anyone who finds a fossil should leave it in place and contact experts to assess it. She says those who collect fossils on their own run the risk of destroying scientific information about their location and context that can’t be recreated.

The next steps in the research will include analyzing samples with a new ion-chromatography instrument recently brought to campus thanks to funding from the National Science Foundation. “Future research done with this instrument will help us better constrain what is driving fossil bone dissolution,” says Keenan.

Sullivan’s success in her master’s research at Mines helped her land a position in the paleontology Ph.D. program at the University of Kansas in Lawrence where she is continuing work on geochemistry of Cretaceous fossils and the surrounding strata that can lend to the understanding of paleoenvironments and dinosaur evolution into modern birds.    



About South Dakota Mines  

Founded in 1885, South Dakota Mines is one of the nation’s leading engineering, science and technology universities. South Dakota Mines offers bachelor’s, master’s and doctoral degrees and a best-in-class education at an affordable price. The university enrolls 2,493 students with an average class size of 24. The South Dakota Mines placement rate for graduates is 98 percent, with an average starting salary of more than $70,036. For these reasons  South Dakota Mines is ranked among the best engineering schools in the country for return on investment. Find us online at www.sdsmt.edu and on FacebookTwitter, LinkedInInstagram, and Snapchat.

Contact: Mike Ray, 605-394-6082, mike.ray@sdsmt.edu