Paleontologists spent 20 years carbon-dating thousands of marine fossils, then used them to decode a process fundamental to Earth’s history
Florida Museum of Natural History
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Scientists carbon-dated more than 7,500 marine fossils from ocean beds around the world and used that data to determine which environmental factors are most responsible for mixing together fossils from different time periods in the same stratum.
view moreCredit: Florida Museum photo by Kristen Grace
Paleontologists spent 20 years carbon-dating thousands of marine fossils, then used them to decode a process fundamental to Earth’s history
Key points
- Over the course of 20 years, an international team of scientists collected and carbon-dated more than 7,500 marine fossils from ocean beds around the world.
- Scientists used the dataset to determine which of several environmental factors contributes most to time averaging, a phenomenon in which organisms that lived in different time periods are mixed and preserved together in the same fossil bed.
- The results indicate that sedimentation is more important than other factors, such as the number of burrowing animals in a given area or the durability of fossils.
- The study, published in the journal PNAS, establishes guidelines regarding the types of research questions paleontologists can investigate using fossil samples.
GAINESVILLE, Fla. --- In productive marine environments, a square meter of seafloor can be perforated by hundreds to thousands of isolated and interconnected tunnels through which crawl and writhe a cornucopia of clams, shrimp, sea stars, sand dollars, snails, worms and other animals. All that excavation mixes up the sediment, along with any shells and other skeletal remains that happen to be there. This temporal smearing is a problem for paleontologists, because when that piece of seafloor is buried and becomes part of the fossil record, it’s difficult and expensive to figure out how much mixing took place.
“What continually amazes me is just how much time a bunch of fossils collected from a single sediment layer can represent. In some cases, well-preserved fossil organisms that are found next to each other might have lived hundreds or thousands of years apart,” wrote Rafal Nawrot, a paleontologist at the University of Vienna.
The mixing of fossils that lived at different times but are preserved together is called time averaging.
According to Daniele Scarponi, a colleague of Nawrot’s and an associate professor at the University of Bologna, time averaging dictates the types of questions paleontologists can ask.
“Before interpreting a fossil assemblage, we need to know the interval it represents. Some fossil assemblages are like the ruins of Pompeii — buried rapidly and thus providing a snapshot of past communities frozen in time. Others are more akin to a prehistoric graveyard used continuously over centuries, in which human remains from different generations are slowly accumulating over time. Both types can provide valuable insights into the past, but the kinds of data we can extract from them will be different in each case,” Scarponi wrote.
In addition to burrowing animals, several other factors influence time averaging, including:
- The durability of organic material is important. Most organisms decompose or get picked apart by scavengers before they become fossilized. For this reason, both the marine and terrestrial fossil records are primarily composed of hard skeletal material, like shells and bones. But even these break and disintegrate if they aren’t preserved quickly enough.
- Another important factor is the rate of sedimentation, which occurs unevenly in different parts of the ocean and changes through time. Deltas, for example, have high rates of sedimentation, whereas other areas might only receive a fine dusting over long periods of time. If sedimentation is slow, skeletal remains of organisms accumulate over long periods of time, but if sedimentation is fast, the remains are buried quicker, and age mixing is reduced.
- Biological productivity is also crucial. The number of fossils paleontologists can expect to find while digging in one spot is strongly correlated with the number of organisms that were previously around to be fossilized in the first place.
Through a project that was 20 years in the making, members of an international consortium of scientists say they have determined which of these factors is the most important for time averaging and thus primarily controls the temporal resolution of paleontological data.
“Our results demonstrate that if we know how quickly sediment accumulates — which can be deduced from the environmental context — we can determine how much time is captured by a given fossil assemblage: The faster individual shells or bones are buried below the sediment surface, the less likely it is that remains from multiple generations of organisms will accumulate and be preserved together,” Nawrot wrote.
Sedimentation rates have long been anticipated to be an important component of time averaging, but gathering data needed to rigorously and comprehensively assess this issue is difficult, time-consuming and very expensive.
By integrating multiple projects, the authors analyzed more than 7,500 fossils, which were dated using radiocarbon and other methods and collected from a variety of oceanic environments around the world, from shallow coastal settings to the edges of continental shelves.
The various research groups involved in the project — which includes scientists based in Australia, Austria, the Bahamas, Brazil, Italy, Germany, Slovakia and the United States — separately collected, studied and published papers on the fossils over a period of two decades. When they learned of each other’s work, they decided to join forces and share data.
“Nothing of this scale has ever been attempted before because it’s simply not feasible to do so, but thanks to the fact that we had a whole bunch of teams that worked on similar topics and used similar methods, we were able to compile it,” said the study’s co-lead author, Michal Kowalewski, the Thompson chair of invertebrate paleontology at the Florida Museum of Natural History.
Radiometric dating, one of the primary methods the authors used, takes advantage of the fact that radioactive atoms always decay into more stable, non-radioactive atoms at a steady, predictable rate. This allows scientists to estimate the age of minerals and fossils.
Many animals have skeletons that contain a type of radioactive isotope called carbon-14. Plants absorb carbon-14 during photosynthesis and use it to make more of themselves. Herbivores get carbon-14 secondhand by eating plants, carnivores get it from herbivores, and decomposers get it from all of the above. This list includes humans. Any part of your body that contains carbon — which is every part of your body — is radioactive. Fortunately, carbon-14 emits radiation in the form of electrons, which for us is kind of like receiving a constant but imperceptibly low-level electric shock — not at all like the cell-shredding gamma rays emitted by uranium.
Carbon-14 has a half-life – the amount of time it takes for half of any given number of radioactive atoms to decay — of around 5,730 years. That meant the authors were restricted to the most recent fossil record, up to 55,000 years old, which is about the cutoff when any remaining carbon-14 in a fossil can be reliably measured.
The researchers also used a technique known as amino-acid racemization, which uses ratios of amino acids. As in the case of carbon isotopes, the ratio of different forms of a given amino acid also changes through time in a predictable way.
The reason no one has attempted dating on such a grand scale before is primarily due to the high cost of radiocarbon and amino-acid dating. Most research groups can afford to obtain data for only a few dozen specimens, but thousands of specimens are needed to fully evaluate the scale and drivers of time averaging. Distributing the cost across multiple labs over two decades helped significantly reduce this barrier, as did recent technological advances in radiometric dating that lowered the cost and made it possible to use much smaller samples than was previously possible.
Through this unique collaboration, Kowalewski and his colleagues have what is possibly the largest collection of fossil carbon dates ever compiled, which can now be used on a variety of research topics that would have been intractable otherwise.
“The dataset is incredibly powerful. We’re now working on multiple follow-up projects that explore various aspects of time averaging and related processes. You can use it to answer a lot of questions, but of course, we started with the big one,” he said.
After compiling the carbon dates from their fossil specimens, the authors simulated age distributions by varying the rates of bioturbation (mixing caused by burrowing animals), sedimentation and fossil destruction. Then they compared the real age distribution of carbon-dated fossils with the different simulated distributions to see which of the models most closely matched the actual patterns observed in the data.
The results were unambiguous.
“Sometimes life turns out to be more exciting than you thought,” Kowalewski said. “In this case, the outcome is beyond any dreams we may have had when we started.”
Knowing that the rate of sedimentation is the single most important factor in determining the extent to which fossils of different ages become mixed will unlock research avenues that were previously restricted. And assuming the same pattern holds true for oceans further back in time, the results can be extended to fossils that are much older than the ones that still contain residual amounts of carbon-14.
The authors published their results in the journal Proceedings of the National Academy of Sciences.
Additional co-authors of the study are: Adam Tomašových of the Slovak Academy of Sciences; Martin Zuschin, Bettina Bachmann, Michaela Berensmeier and Jan Steger of the University of Vienna; Paolo Albano of the Stazione Zoologica Anton Dohrn; Quan Hua of the Australian Nuclear Science and Technology Organisation; Darrell Kaufman of Northern Arizona University; Susan Kidwell of the University of Chicago; Matias Ritter of the Universidade Federal do Rio Grande do Sul; Marcello Simões of the Universidade Estadual Paulista; Luis Torres Jr. of the Florida Museum of Natural History; Lukas Schweigl of the University of Bologna; Troy Dexter of the University of The Bahamas; Ivo Gallmetzer of the Natural History Museum Vienna; Claudio Pellegrini of the National Research Council of Italy; and Matthew Kosnik of Macquarie University.
Journal
Proceedings of the National Academy of Sciences
Article Title
Sediment accumulation rate predicts the temporal resolution of marine fossil assemblages
SUNY Potsdam Faculty awarded National Science Foundation grant to study paleosalinity of ancient sedimentary rocks
SUNY Potsdam professors Dr. Page Quinton and Dr. Michael Rygel awarded $411,477 from National Science Foundation to further research on Devonian-Permian sedimentary rocks
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Seen here placing minerals in the Geology Museum displays at SUNY Potsdam, Dr. Michael Rygel (left) and Dr. Page Quinton (right) were recently awarded a new grant from the National Science Foundation to support their research on the salinity of ancient sedimentary rocks.
view moreCredit: Dr. Page Quinton
Two SUNY Potsdam geoscientists have been awarded a National Science Foundation grant to investigate the chemistry of ancient waters preserved in sedimentary rocks across Atlantic Canada, research that could shed new light on the evolution of life on land and the distribution of energy and mineral resources.
Dr. Page Quinton and Dr. Michael Rygel, faculty members in SUNY Potsdam’s Department of Earth and Environmental Sciences, were recently awarded $411,477 from the NSF for their project, "Salinity, Source Rocks, and Cyclothems: Using Paleosalinity Proxies to Track Marine Influence in the Maritimes Basin.” This three-year project will provide paid research experiences for SUNY Potsdam undergraduates and will involve field work in Nova Scotia, New Brunswick, Prince Edward Island and Newfoundland.
Learn more: Earth and Environmental Sciences at SUNY Potsdam
“Beyond its pure scientific value, gaining a better understanding of the chemistry of these ancient waters could potentially improve our understanding of the distribution of energy and mineral resources in this part of the world,” Quinton said. “The techniques are new, and our background and expertise make us uniquely well qualified to do this work. Many of these rocks are exposed along remote and rugged parts of the coast… some are even along the shore of the Bay of Fundy and subject to the world’s highest tides.”
The Maritimes Basin contains thousands of feet of Devonian-Permian (about 419 to 251-million-year-old) sedimentary rocks of global significance. These strata comprise two UNESCO World Heritage Sites, have supported more than 200 years of resource-based economic activity, and have yielded important insights into Earth's organisms, ecosystems and evolutionary patterns.
“The rocks that we will be working on in Atlantic Canada provide a remarkably detailed and complete record of life fully conquering the terrestrial realm. Specifically, these rocks contain things like trackways of early amphibians, skeletal material from the oldest unequivocal reptiles, the first land snails, spectacular fossilized forests, the oldest evidence of parental care in synapsids (mammals and their extinct mammal-like ancestors), and the first evidence of coordinated movement of groups of organisms across the landscape,” Rygel said. “All of these things happened in or adjacent to wetlands that could have been fresh, brackish, or marine … we have no idea. Geologists have been wondering about the chemistry of these wetlands for nearly 200 years, and I’ve been thinking about it for over 25 years.”
Despite the importance of these rocks, fundamental questions about water chemistry during their deposition remain unanswered. This research will identify intervals that were influenced by marine waters and provide new information about the conditions that shaped the evolution of plant and animal life on land and the nature and distribution of economic resources in the basin.
“Traditionally, understanding how salty the waters were requires finding certain types of fossils. Despite nearly 200 years of looking, we’ve not found more than a handful of useful fossils. It could be that we’ve just not found them yet, it could be that something about the water chemistry made it difficult for certain types of life, or maybe the conventional approaches don’t work there. Rather than hoping we get lucky and finding the right kind of fossils, the new geochemical techniques that we will use will allow us to analyze the rocks directly and determine the chemistry of the waters that they formed in,” Quinton said.
The project will also provide paid hands-on research experience for undergraduate students, as well as teaching and research experience for future K-12 Earth science teachers—giving SUNY Potsdam undergraduates the opportunity to take part in high-impact practices.
“We will have our students participate in every aspect of the research process and operating as a research team will be great preparation for graduate school or the workforce. This experience will make them more competitive for what comes next because it will provide them with direction about what kinds of projects (field-based, lab-based, or both) they are interested in pursuing,” Rygel said. “These kinds of experiences allow students to take the theory they learn about in lecture and the skills they learn in lab and apply them to real world problems.”
This is not the first NSF-funded collaboration for Quinton and Rygel. In 2021, they received a $370,113 NSF Research in Undergraduate Institutions grant to investigate Earth's ancient climate cycles while mentoring student researchers through field studies in Montana and Texas.
They have also collaborated on developing a campus Geoscience Garden, and co-authored an open educational research textbook to benefit their students.
Dr. Page Quinton is a stable isotope geochemist who studies the connection between the carbon cycle, ancient climate change, and major mass extinction events. Research she conducted with colleagues at El Kef, Tunisia, received international attention when it was published in the journal Science in 2018. Recent work has included research focusing on the role of climate change in the dinosaur mass extinction event, understanding the impact of early land plants on shallow seas, and understanding the connection between sea level change and carbon cycling. This work has taken her to Australia, Canada and all over the U.S.
Dr. Michael Rygel has deep family ties to the steel mills and coal mines of western Pennsylvania, and his research focuses on understanding the Paleozoic-aged rocks that these industries were built on. Specifically, he is a sedimentologist and stratigrapher who specializes in understanding ancient environments. His past research projects have focused on outcrops in the coal-bearing rocks in the Appalachian Basin in Pennsylvania and West Virginia, and the Maritimes Basin in Atlantic Canada, as well as coeval ancient glacial deposits in southeastern Australia.
SUNY Potsdam’s Department of Earth and Environmental Sciences prepares students for in-demand careers in the sciences, or for further study on the graduate or professional level. The department offers majors in environmental science and geology, including an option leading to geologic licensure, with a strong focus on both lab and field experience. SUNY Potsdam’s location in the St. Lawrence Valley near the Adirondack Mountains provides a natural laboratory for students.
About SUNY Potsdam:
Founded in 1816, The State University of New York at Potsdam is one of America’s first 50 colleges—and the oldest institution within SUNY. Now in its third century, SUNY Potsdam is distinguished by a legacy of pioneering programs and educational excellence. The College currently enrolls approximately 2,500 undergraduate and graduate students. Home to the world-renowned Crane School of Music, SUNY Potsdam is known for its challenging liberal arts and sciences core, distinction in teacher training and culture of creativity. To learn more, visit www.potsdam.edu.
