Geologists shed light on the evolution of life 800 million years ago – ScienceDaily

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A team of Virginia Tech geoscientists has discovered evidence that might indicate yes.

The team’s findings, recently published in Science Advances, reveal an increase in bioavailable nitrogen during the time when marine eukaryotes—organisms whose cells contain a nucleus—became dominant. Complex eukaryotic cells evolved into multicellular organisms and are credited with ushering in an entirely new era of life on Earth, including animals, plants, and fungi.

“Where we sit today, with life as it is on this planet, is the sum of all the events that happened in the past,” said Ben Gill, associate professor of sedimentary geochemistry and co-author on the paper. “And this is a key event where we go from dominant prokaryotic ecosystems—cells that are much simpler than those in our bodies—to eukaryotes. If that hadn’t happened, we wouldn’t be here today.”

Previous research focused on the role of phosphorus in the emergence of eukaryotes, but Junyao Kang, a doctoral student in the Department of Earth Sciences and lead author of the paper, was interested in the role nitrogen plays in this event.

“This data is unique because nitrogen isotope data is virtually non-existent from the early Neoproterozoic time period, or between 1 billion and 800 million years ago,” Kang said.

In collaboration with Nanjing University in Nanjing, China, Kang spent two years working to understand what drove the rise of eukaryotes by analyzing nitrogen isotopes of rock samples from North China’s Craton. Home to rocks dating back 3.8 billion years, the area was once covered in ocean.

“We had some rough ideas about when eukaryotes became ecologically successful,” said Shuhai Xiao, professor of geobiology and one of the paper’s authors. “They stayed there for a long time in a low-level status until about 820 million years ago, when they became abundant.”

Kang decided he wanted to know why. He took data from rock samples, entered it into a larger database, and analyzed it over a longer time scale that spanned different geographic locations.

“Once we did this kind of integration and put it into a big picture, we saw nitrate rise through time, which is what happened about 800 million years ago,” Kang said.

Strong collaboration

An international collaborative approach was key to linking these new data to biological events, in particular the emergence of eukaryotes.

Gill and Rachel Reid, also a Geochemist in the College of Science and co-author of the paper, provided critical analyzes through resources, including mass spectrometry at the Stable Isotope Laboratory in Geosciences at Virginia Tech. An elemental analyzer coupled to a mass spectrometer allows researchers to extract pure nitrogen gas from samples for analysis.

Jill specializes in reconstructing our planet’s current and past chemical cycles. He collaborates with paleontologists to study the record of life preserved in the geological record and examines possible environmental factors that may have enabled changes in life throughout history.

Reid, whose research generally focuses on recent events on Earth, had a special opportunity to offer her expertise on nitrogen isotopes for these ancient fossils.

Feifei Zhang, a geochemist at Nanjing University, was the fourth co-author of the paper. Zhang provided insights into how much oxygen would have been available in the oceans during a time when nitrates were abundant.

All of the Virginia Tech authors are affiliate members of the Fralin Life Sciences Institute’s Center for Global Change, where Kang serves as a Ph.D. Fellow in the Interfaces to Global Change graduate program. The Center brings together experts from various disciplines to solve these complex global challenges and train the next generation of leaders.

Past, present and future

This kind of study gives him hope for future discoveries, said Xiao, who has helped excavate and study some of the oldest fossils from around the world. Team members look forward to collaborating with NASA on future grants, such as the Exogenous Biology Program, that support their current research.

He also credits the University Libraries at Virginia Tech for its support of open access publications, such as Science Advances, for making a selection of research available, freely available to readers.

“We can connect the dots from nitrogen isotopic compositions in the ancient past and then go to the next step and infer the amount of nitrate available to organisms,” Xiao said. “Then we correlate that with the fossil data to show that there is a relationship.”

While the ancient oceans are long gone, what happened in the ancient oceans was recorded in rocks, and the study of these rocks provides a link from Earth’s history to the present and future.

“Geologists look at rocks for the same reason stock traders look at the Dow Jones curve when they make decisions to buy or sell stocks,” Xiao said. “The geological history written in rocks gives us important context about future global changes.”

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