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The atmosphere, ocean, and life on Earth have interacted over the past 500 million years in ways that have improved the conditions for early organisms. Now, an interdisciplinary team of scientists has produced a review paper on this co-evolutionary story, published in National Science Review.
“One of our tasks was to summarize the most important discoveries about carbon dioxide and oxygen in the atmosphere and ocean over the last 500 million years,” says Zunli Lu, a professor of geochemistry at Syracuse University and lead author of the study. “We looked at how these physical changes affected the evolution of life in the ocean. But it’s a two-way street. The evolution of life also impacted the chemical environment. It’s not an easy task to figure out how to build a habitable Earth over long time scales.”
The team from Syracuse University, the University of Oxford and Stanford University explored the complex feedbacks between ancient life forms, including plants and animals, and the chemical environment of the current Phanerozoic eon, which began about 540 million years ago.
At the beginning of the Phanerozoic, carbon dioxide levels in the atmosphere were high and oxygen levels were low. Such conditions would have made it difficult for many modern organisms to survive. But marine algae changed that. They absorbed carbon dioxide from the atmosphere, locked it into organic matter, and produced oxygen through photosynthesis.
The ability of animals to live in an ocean environment was affected by oxygen levels. Lu studies where and when oxygen levels in the oceans may have increased or decreased during the Phanerozoic using geochemical proxies and model simulations. Co-author Jonathan Payne, a professor of Earth and planetary sciences at Stanford University, compares an ancient animal’s estimated metabolic needs to where it survived or disappeared in the fossil record.
Photosynthetic algae removed atmospheric carbon into sedimentary rocks to reduce carbon dioxide levels and increase oxygen levels. As a result, the algae’s enzymes became less efficient at fixing carbon. As a result, the algae had to create more complex methods to photosynthesize at lower carbon dioxide and higher oxygen levels, and they did this by creating internal compartments for photosynthesis with control over the chemistry.
“For algae, it is the changes in the environmental ratio of O2/CO2 “These changes appear to be key to improving photosynthetic efficiency,” says co-author Rosalind Rickaby, professor of geology at Oxford. “What’s really intriguing is that these improvements in photosynthetic efficiency may have expanded the chemical envelope of habitability for many forms of life.”
Ancient photosynthesizers had to adapt to changes in the physical environment they themselves had created, Lu notes. “The first part of the Phanerozoic story is about increasing the habitability of life, and then the second part is about adaptation.”
If scientists want to better understand this interaction between life and the physical environment, as well as the drivers and limits of habitability, the authors suggest that mapping spatial patterns of ocean oxygen, biomarkers of photosynthesis, and metabolic tolerance of animals present in the fossil record will be a key direction for future research.
More information:
Zunli Lu et al., Phanerozoic coevolution of O2-CO2 and the habitability of the oceans, National Science Review (2024). DOI: 10.1093/nsr/nwae099
Provided by Syracuse University
Quote:Scientists untangle interactions between Earth’s earliest life forms and the environment over 500 million years (2024, July 29) retrieved July 30, 2024 from https://phys.org/news/2024-07-scientists-untangle-interactions-earth-early.html
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