USU scientists believe organisms went extinct before dinosaurs
Before the dinosaurs, there were microscopic organisms, and USU doctoral student Dawn Hayes, along with assistant professor Carol Dehler, believes these single-celled creatures saw a mass extinction.
Dehler and Hayes, both in the geology department, are studying the sedimentary rocks of the Uinta Mountains and said their research suggests an extinction of single-celled organisms well before the evolution of animals. Dehler said they look at sedimentary rocks because of the layers within the rocks, which date back 750 million years, pre-dating the evolution of animals by 185 million years.
Sedimentary rocks are formed when sediments pile on top of each other and are pressed together with incredible pressure. Among the different types of sedimentary rocks are limestone, sandstone and shale, or compacted mud. This is the type of rock they are focusing on, said Dehler, who even keeps bags of the black shale on her desk.
Dehler said they are interested in this specific rock type because it is organic-rich. She said that when looked at under a microscope, the shale exposes a “microbial world.” By studying these fossil records, Dehler and Hayes found a “biotic change.”
Hayes said it was originally believed that glaciations from a significant period of climate change, known as Snowball Earth, wiped out the single-celled organisms. The team found this may not be accurate.
“We found low-diversity, high populations of fossil assemblage under rocks that record the glaciation,” Dehler said. “This biotic change had already happened.”
Hayes explained that this means bacterium caused the extinction of the single-celled organisms, like algae and plankton. There was a sudden shift, she said, from single-celled organisms to a bacterial-dominated world, which could have been due to a change in ocean chemistry. By studying the shale they found in the Uinta mountains, they can see this change because of oxygen levels and the organic matter in the rock.
Hayes said they’re hypothesis is that a period of high sulfur content along with an algae-bloom-like spread of bacteria erupted throughout the oceans world wide and killed off the earlier organisms.
Dehler said this new information raises a questions: could this biotic change have been a precursory event to climate change? If these bacteria bloomed worldwide, could it have caused the climate change?
“We’re constantly learning and we’re constantly becoming new scientists because it moves so fast,” she said.
Dehler’s interest in fossils of this kind began on a trip to the Grand Canyon in 1995, where she first took notice of these Pre-Cambrian rocks. She said it was “love at first sight” and at the time wondered if they had been studied yet. Though some research had been done on the rocks, it wasn’t in-depth and Dehler began her study of the fossils. She said the research has now piqued the interest of scientists in many fields.
Hayes was originally a biology and chemistry teacher, then returned to USU to work toward her graduate degree. She recently presented the team’s research to the Geological Society of America and said she looks forward to continuing the research.
Contrary to a recent article, Hayes said they are “definitely not challenging the idea the earth was at one point or a few points covered in glaciers.” Hayes is currently working on her doctoral thesis, which is focused on the evolution and decline of snowball earth. She and Dehler are working on a grant proposal that would allow them to test other areas of the Uinta mountains to see if they have similar results.
As they try to find a specific reason for this early extinction, Dehler said they’ve recognized there are probably many reasons.
“One of the important things about looking at older fossil records,” she said, “is looking at what earlier fossils can tell us: how animals evolved, how many other extinctions happened and how organisms became extinct.”