These two geochemists have one of the largest publishing networks in science

A ‘power couple’ in Earth and environmental sciences.

26 June 2020

Image of Larry Edwards by Layne Kennedy

Hai Cheng (left) and Larry Edwards (right) use uranium-thorium dating techniques to determine the age of cave rocks, which reveals insights about the timing of events that have occurred in the last half a million years.

Geochemists Larry Edwards and Hai Cheng want to reconstruct the last half a million years on Earth in more detail than ever before.

After a chance meeting at a lab party almost three decades ago, the pair have developed some of the most powerful dating techniques in their field.

While conventional radiocarbon dating can reach back 40,000 years, Edwards and Cheng’s approach to uranium-thorium dating can reconstruct the past 600,000 years.

Their improvements to uranium-thorium dating, which estimates the age of a rock based on how much uranium and thorium it contains, have enabled researchers to track the rise and fall of ancient civilizations, the forming and melting of ice sheets, and abrupt fluctuations in Earth’s climate.

“We see ourselves as the timekeepers of the last chapter of Earth’s history,” says Edwards.

A lasting impact

Edwards’ big-picture thinking and Cheng’s highly technical skillset set the pair up for early success.

As a graduate student at the California Institute of Technology in Pasadena during the late 1980s, Edwards developed new methods of measuring the rare isotopes, uranium and thorium, using mass spectrometry, a highly sensitive technique for determining the mass of atoms and molecules.

While this approach greatly increased the accuracy of uranium-thorium dating, Edwards wanted to use the next generation of mass spectrometers to make further improvements to his technique, such as increasing its time range and reducing the size of rock samples required.

In the 1990s, in his fledgling lab at the University of Minnesota, Edwards wanted a collaborator who could turn his ambitious ideas into viable research projects. Hai Cheng, who had been studying isotope geochemistry and mass spectrometry at Macquarie University in Sydney, Australia, had the practical skills needed to improve the accuracy of his technique.

So when Cheng showed up at a lab party in 1993 after moving to Minnesota to be with his family, Edwards “pretty much hired him on the spot.”

“He’s incredibly capable on all fronts,” says Edwards.

Impressive network

According to Dimensions data, Edwards and Cheng have co-authored 304 papers since 1997, including 130 articles in the 82 high-quality journals tracked by the Nature Index.

In 2019 alone, they co-authored 14 Earth and environmental sciences papers in Nature Index journals, which is more than any other research pair in their field.

Below is Edwards and Cheng’s co-authorship network in 2019 for Earth and environmental sciences papers published in Nature Index journals.

Zoom in and hover the mouse over the lines to view the number of co-publications between authors, as shown by link strength:

Global team builders

An important part of Edwards and Cheng’s work is developing and maintaining partnerships with roughly 400 researchers from around the world.

These collaborations have helped them collect samples from some of the most challenging locations, such as Hulu Cave near the city of Nanjing in China and coral reefs at Devil’s Claw in the Galápagos Islands of Ecuador.

“Our work requires people who have the skills to go into the field at several locations,” says Cheng, who is now based at the Xi'an Jiaotong University in Shaanxi, China. “We are working globally.”

Among these collaborators is Ashish Sinha, a palaeoclimatologist at California State University in Dominguez Hills, who found a link between changing rainfall patterns and the rapid collapse of the Neo-Assyrian Empire in 609 BC using Edwards and Cheng’s uranium-thorium technique.

A 2019 Science Advances paper that Edwards and Cheng co-authored with Sinha has been covered by 49 news outlets and more than 250 Twitter users so far, according to an Altmetric analysis.

Edwards says teaming up with international researchers with similar goals has helped him and Cheng maintain their momentum as partners.

“We’re really good at what we do, which attracts researchers who are passionate about this work,” says Edwards. “If we work together, we’re better off. That’s been our philosophy for years.”

Data used was sourced from Dimensions, an inter-linked research information system provided by Digital Science (https://www.dimensions.ai).

The network map was created using VOSviewer.