A recent deep-sea discovery is changing how scientists understand the evolution of complex life on Earth. Researchers found that some ancient microbes, called Asgard archaea, are able to use oxygen. This finding challenges earlier beliefs that these microbes only lived in environments without oxygen. This ability suggests that the ancestors of complex life forms, known as eukaryotes, may have also used oxygen. Scientists say this could have been a critical step for life to become more diverse and intricate.[indiandefencereview+2]
Ancient Microbes and Oxygen's Role
The new research focuses on Asgard archaea, a group of microbes considered close relatives to the ancestors of complex life. Traditionally, scientists thought these microbes thrived only in deep-sea areas where no oxygen was present. However, new genomic sequencing has shown that some Asgard archaea can tolerate and even use oxygen.[indiandefencereview+2]
Brett Baker, an associate professor of marine science at the University of Texas at Austin, explained this important shift. He said that while most modern Asgards live without oxygen, those most closely related to eukaryotes are found in oxygen-rich places. These include shallow coastal sediments and open water.Baker noted these oxygen-using Asgards have many metabolic pathways that use oxygen.[indiandefencereview+2]
This suggests that the common ancestor of eukaryotes likely possessed these same oxygen-using abilities.Baker added that Asgards adapted to the presence of oxygen, gaining an energetic advantage. This adaptation then allowed them to evolve into eukaryotes, the cells that make up plants, animals, and fungi.This process may have provided the energy needed for complex cellular structures to develop.[indiandefencereview+4]
Earth's Oxygen History and Life's Emergence
Earth's history saw a dramatic increase in oxygen levels in the atmosphere and shallow seas during the Great Oxidation Event (GOE). This period began approximately 2.46 billion years ago and ended around 2.06 billion years ago.This profound change was largely due to cyanobacteria, microorganisms that evolved the ability to perform photosynthesis.Cyanobacteria produce oxygen as a byproduct of using sunlight and water for energy.[en+4]
Cyanobacteria first appeared around 2.9 billion years ago, meaning they produced oxygen for hundreds of millions of years before the GOE.Early oxygen was likely absorbed by rocks and other geological processes.The rise in oxygen during the GOE created conditions closer to what we experience today.Shortly after this event, the first fossil evidence of eukaryotes appeared, suggesting a strong link between rising oxygen and the evolution of more complex cells.[biotechniques+4]
Shallow oceans became oxygenated fairly quickly, geologically speaking, after oxygen began accumulating in the atmosphere.Studies show that shallow ocean waters contained significant oxygen as early as 2.32 billion years ago.This early oxygenation of surface waters was a crucial precursor to deeper ocean changes.[universetoday+5]
Deep Ocean's Complex Oxygen Story
The oxygenation of the deep ocean was a much more complex process than once thought. It did not happen all at once, but rather in several phases over vast stretches of time.For a long time, deep ocean environments remained largely oxygen-free, even as surface waters gained oxygen.[sciencedaily+4]
One significant and permanent deep-ocean oxygenation event occurred about 390 million years ago.This boost in deep-sea oxygen was fueled by the spread of woody plants on land, which are the ancestors of Earth's first forests.This led to a revolution in ocean life, allowing jawed fish and other larger marine animals to expand, diversify, and grow.Michael Kipp, an assistant professor at Duke University, said this study strongly suggests oxygen dictated the timing of early animal evolution, especially for jawed vertebrates in deep-ocean habitats.[sciencedaily+7]
However, the deep ocean's oxygen levels were not always stable. New research indicates that oxygen levels at the ocean floor fluctuated wildly long after the Cambrian Period, when animal life diversified.Sustained oxygen accumulation in global deep marine waters likely happened sometime after 380 million years ago.[attheu+3]
Surprising "Dark Oxygen" Discovery
Adding another layer of complexity to the story of oxygen is the recent discovery of "dark oxygen." An international team of researchers found that metallic minerals on the deep-ocean floor can produce oxygen in complete darkness. This process happens more than two miles below the Pacific Ocean surface, where no sunlight can penetrate.[m+2]
This surprising finding challenges the long-held scientific belief that oxygen production relies solely on sunlight and photosynthesis.Andrew Sweetman of the Scottish Association for Marine Science, who made the discovery, stated that this requires rethinking how aerobic life might have begun.Franz Geiger, a Northwestern University chemist, explained that polymetallic nodules, which are natural mineral deposits, are at the heart of this discovery.These nodules contain metals like cobalt, nickel, and manganese.[m+5]
The existence of "dark oxygen" has significant implications for understanding life's origins on Earth and potentially elsewhere in the universe.It also raises questions about deep-sea mining, as these nodules are targeted for extraction.Professor Nicholas Owens, Director of SAMS, called it one of the most exciting findings in ocean science in recent times.He emphasized that an alternative source of oxygen requires a radical rethink of how complex life on the planet might have originated.[m+5]
Ongoing Scientific Debate
While many studies highlight oxygen's crucial role, the relationship between oxygen and the evolution of complex life is not always straightforward. One study published in 2023 suggests that the "Avalon explosion" of multicellular organisms, which occurred between 685 and 800 million years ago, happened during times of surprisingly low oxygen levels.[futurity]
Christian J. Bjerrum, an associate professor at the University of Copenhagen, said measurements showed no major increase in oxygen when more advanced fauna began to evolve.He even noted a slight decrease.Bjerrum suggested that organisms might have benefited from lower oxygen levels, allowing them to develop in an environment where water chemistry protected their stem cells.This indicates that Earth's evolutionary path is complex and involves many interacting factors beyond just oxygen.[futurity+2]
Scientists continue to explore the intricate connections between Earth's changing oxygen levels and the remarkable journey of life's evolution. New discoveries from the deep sea are continuously reshaping our understanding of this ancient story.
