For over 500 million years, the atmosphere, oceans, and life on Earth have interacted in ways that helped early organisms thrive.
A team of scientists from Syracuse University, Oxford University, and Stanford University has published a study in National Science Review exploring this co-evolutionary history.
“One of our tasks was to summarize the most important discoveries about carbon dioxide and oxygen in the atmosphere and ocean over the past 500 million years,” says Zunli Lu, a geochemistry professor at Syracuse University and the lead author of the paper.
“We looked at how these changes affected life in the ocean and how the evolution of life impacted the chemical environment. Understanding how to build a habitable Earth over long periods is not easy.”
The study focuses on the Phanerozoic Eon, which began around 540 million years ago.
At the start of this period, carbon dioxide levels were high, and oxygen levels were low, making it difficult for many modern organisms to survive.
Ocean algae played a crucial role in changing this by absorbing carbon dioxide from the atmosphere, locking it into organic matter, and producing oxygen through photosynthesis.
Animals’ ability to live in the ocean was influenced by oxygen levels.
Lu and his team used geochemical proxies and model simulations to study where and when ocean oxygen levels changed during the Phanerozoic. Co-author Jonathan Payne, a professor of Earth and planetary sciences at Stanford University, compared ancient animals’ metabolic needs to where they lived or disappeared in the fossil record.
As algae removed carbon dioxide from the atmosphere and increased oxygen levels, their enzymes became less efficient at fixing carbon.
To adapt, algae developed more complex ways of performing photosynthesis, creating internal compartments to control the chemistry.
“For algae, it is changes in the environmental ratio of O2/CO2 that seem to be key to driving improved photosynthetic efficiency,” says Rosalind Rickaby, a geology professor at Oxford. “These improvements in photosynthetic efficiency may have expanded the conditions for many forms of life to thrive.”
Ancient photosynthesizers had to adapt to the changes in the environment they created. “The first part of the history of the Phanerozoic is increasing habitability for life, and the second part is adaptation,” notes Lu.
To better understand how life and the environment have interacted and the limits on habitability, the authors suggest future research should map out the spatial patterns of ocean oxygen, biomarkers for photosynthesis, and the metabolic tolerance of animals shown in fossil records.
This will help scientists gain deeper insights into the complex interplay between life and the Earth’s physical environment over millions of years.
