ASU-led team defends molecular oxygen findings

Researchers point out weaknesses, limits of competing study

April 10, 2023

When did molecular oxygen, the gas that all large and complex forms of life on Earth today require to function, first appear on Earth?

For more than 15 years, work by a team of scientists led by Ariel Anbar, a professor in Arizona State University’s School of Earth and Space Exploration and School of Molecular Sciences, has advanced the case that this biologically critical gas first appeared at least 2.5 billion years ago. Beginning with a pair of studies published in 2007, the team analyzed the chemistry of sedimentary rocks laid down on the ancient seafloor. Close-up photo of living stromatolites at Shark Bay, Western Australia. Living stromatolites at Shark Bay, Western Australia. Oxygen produced by ancient stromatolites may have left its mark on Earth's environment as early as 2.5 billion years ago. Photo courtesy Ariel Anbar Download Full Image

The results revealed evidence of the gas in oceans 2.5 billion years ago, long before conventional wisdom said it should have been around. Today, numerous subsequent studies have bolstered the case for this early “whiff” of molecular oxygen 

The findings stirred debate in the scientific community. The latest word in that debate was published April 7 in Science Advances by Anbar and his team. In “Technical Comment on 'Re-examination of 2.5-Ga 'whiff' of oxygen interval points to anoxic ocean before GOE,'" they address a recent challenge to their groundbreaking study.  

The challenge emerged last year. According to a study led by researchers at Caltech and published in 2022, the 2007 interpretations were incorrect. The scientists argued that the rocks examined by Anbar and his team were not well preserved, and so cannot be used to track changes in Earth’s ancient environment.   

“It’s great to see others generate new data to try to challenge the assumptions underlying our work,” Anbar said. “The ancient record is complicated, so these rocks demand careful and constant scrutiny. But we did not find their arguments persuasive.” 

The history of oxygen in the form of the oxygen molecule on Earth draws intense interest from many scientists because it is produced by photosynthesis. So, knowing when it first started to leave a mark on the environment is a way of learning about the history of life itself.   

Scientists know that biological oxygen molecule production left a big mark on Earth starting about 2.4 billion years ago, after what is often called the Great Oxidation Event. But what came before? Sometimes the debates are heated. 

Reviewing the 2022 study, Anbar and his team found that the two research groups were comparing apples and oranges. Whereas the original study focused on the overall chemistry of the rocks, the challengers focused on small nodules and veins made of pyrite — commonly known as fool's gold.

“The new data are exquisite, but they aren’t very relevant to understanding ancient oceans,Anbar said. “The pyrite nodules grew when hot fluids passed through these rocks well after they had first formed. We’ve always known these nodules existed. In our work, we tried to avoid this fool's goldInstead, we focused on the chemistry of the entire rock because that’s a way to see through this kind of alteration.  

In addition to pointing out the late formation of the pyrite nodules, the team’s critique highlighted several other weaknesses in the challengers’ arguments, especially a failure to address the full range of inorganic geochemical evidence of oxygen molecules that has emerged since the 2007 papers. 

We stand by our original study,Anbar said. “But the debate is important! Science isn’t only about getting the right answer. It’s also about poking at what others think is right to see if there are any holes. We only know if our ideas are right if they can stand up to scrutiny. Ours did.” 

Media Relations and Marketing Manager, School of Earth and Space Exploration


ASU exhibit at Arizona Science Center sees state through future generations' eyes

April 10, 2023

Adult siblings Lucas and Isabela debate innovation against tradition as they run their family farm. Twin teens Zoe and Ava ponder whether they will live on Earth or shift their career aspirations off-planet.

These stories are the core of  “Mission Future: Arizona 2045,” a new exhibition at the Arizona Science Center. The interactive experience, developed by Arizona State University, opened early this year and combines space and earth science, storytelling and hands-on elements.  Two young girls use their hands to manipulate an electronic map at the "Mission Future" exhibition, located at the Arizona Science Center “Mission Future — Arizona 2045” opened early this year. Photo courtesy NISE Network Download Full Image

“‘Mission Future: Arizona 2045’ allows guests to see ourselves in our potential collective future as Arizonans,” said Sari Custer, chief of science and curiosity at the Arizona Science Center“We’re thrilled to be able to partner with (Arizona State University), the National Informal STEM Education Network and NASA to bring this exhibit to life and help participants think about the impact their everyday actions have on our immediate ecosystem.”

Through following perspectives of Lucas, Isabela, Zoe and Ava via video recordings, audiences of all ages are prompted to think about a future driven by human actions both on and off Earth. 

“We’re seeing the future through the eyes of generations that will inherit the planet from us,” said Paul Martin, a research professional in the School for the Future of Innovation in Society and co-director of the Center for Innovation in Informal STEM Learning, or CIISL. “Mission Future takes us to the future, but it’s close enough to the present that it’s still real. The person telling you their story could be your child or grandchild.” 

Visitors are guided through the experience by a fifth fictional character: AILI is an Artificial Intelligence Learning Investigator studying how humans interact with systems to create desirable future outcomes. The guide tells visitors that they are not a real person, but they are still alive — “don’t overthink it.” 

Martin said AILI was created with a combination of AI and human efforts. Her voice and general design were both created by AI, which serves as an example of how quickly technologies can advance. 

“We were excited to actually have AI be involved in the exhibit,” said Rae Ostman, a research professor in the School for the Future of Innovation and Society, in the College of Global Futures, and co-director of CIISL. “The exhibit focuses mostly on climate change and earth and space exploration, but including AILI was a way to weave in the idea that a lot of things will be different in our future, including how we’re interacting with AI.” 

Ostman said it was important to find a balance between unexpected changes and present-day familiarities, both for realism of the experience and to support the exhibition’s self-guided nature. 

“It’s an immersive space where you can do activities without being given a list of instructions,” she said. “You draw more information from the context clues put around the activities, so it really puts you in the world.” 

Ostman and Martin, both senior global futures scientists with ASU’s Julie Ann Wrigley Global Futures Laboratory, agree that the future shown in “Mission Future: Arizona 2045” is just one possibility. 

“What will the future be like?” AILI asks exhibition visitors. “That’s for us to decide.” 

Katelyn Reinhart

Communications specialist, Julie Ann Wrigley Global Futures Laboratory