Science & Technology (Commonwealth Union) – Taking into account oxygen is an essential and ever-present component of Earth’s atmosphere at present, imagining a world without oxygen may be impossible. What is astonishing to many is that It only became a lasting part of the atmosphere roughly 2.3 billion years ago, during a transformative interval called the Great Oxidation Event (GOE), which paved the way for the development of oxygen-dependent life.
New research from MIT indicates that certain early organisms may have developed the capacity to use oxygen hundreds of millions of years before the GOE occurred. These results could represent some of the oldest known signs of aerobic respiration on the planet.
In a paper published in Palaeogeography, Palaeoclimatology, Palaeoecology, MIT geobiologists investigated the evolutionary history of a crucial enzyme that allows living things to process oxygen. This enzyme is present in most modern oxygen-breathing organisms. The researchers found evidence that it first emerged during the Mesoarchean era — a geological timeframe that predates the Great Oxidation Event by hundreds of millions of years.
Their findings may shed light on a long-standing mystery in Earth’s past: why atmospheric oxygen took so long to accumulate.
Earth’s earliest oxygen makers were cyanobacteria — microscopic organisms that developed the capacity to harness sunlight and water for photosynthesis, producing oxygen as a waste product. Evidence suggests these microbes appeared about 2.9 billion years ago. That means they were likely generating oxygen for hundreds of millions of years before the Great Oxidation Event. The mystery is: what happened to all that early oxygen?
Researchers have long thought that much of it was absorbed by rocks through chemical reactions. But a new study from an MIT team indicates living organisms may also have been involved.
The scientists discovered that certain life forms may have evolved an oxygen-using enzyme hundreds of millions of years before the Great Oxidation Event. This enzyme could have allowed organisms living alongside cyanobacteria to quickly consume the small amounts of oxygen being produced, slowing its buildup in the atmosphere for a vast stretch of time.
The study co-author Fatima Husain, a postdoctoral researcher in MIT’s Department of Earth, Atmospheric and Planetary Sciences indicated that it really reshapes our understanding of aerobic respiration. She pointed out that their findings support the growing idea that life may have started exploiting oxygen far earlier than what was once believed and it highlights just how inventive life has been throughout Earth’s history.
The paper’s additional co-authors are Gregory Fournier, an associate professor of geobiology at MIT, and Haitao Shang and Stilianos Louca from the University of Oregon.
The new research builds on decades of MIT studies focused on reconstructing the history of oxygen on Earth. Previous work has clarified both the timing of the Great Oxidation Event and the earliest signs of oxygen-producing cyanobacteria. Together, these findings suggest that cyanobacteria began generating oxygen roughly 2.9 billion years ago, while the Great Oxidation Event — the point when oxygen accumulated in the atmosphere in lasting amounts — occurred much later, about 2.33 billion years ago.
For Husain and her team, the long gap between oxygen’s initial appearance and its stable presence in the atmosphere raised an important question.
“We know that the microorganisms that produce oxygen were around well before the Great Oxidation Event,” explained Husain. “So it was natural to ask, was there any life around at that time that could have been capable of using that oxygen for aerobic respiration?”
If some organisms really were consuming oxygen, even in tiny quantities, they may have helped delay the accumulation of oxygen in the atmosphere, at least temporarily.
To explore this idea, the MIT researchers focused on heme-copper oxygen reductases — a family of enzymes crucial for aerobic respiration. These enzymes convert oxygen into water and are present in most oxygen-breathing life today, from bacteria to humans.
Husain indicated that they concentrated on the central part of the enzyme in their analysis, since that is the site where oxygen actually reacts.
