Early Oxygen Use Identified

A new study by MIT researchers suggests that some early forms of life may have developed the ability to utilize oxygen hundreds of millions of years before it became a permanent fixture in Earth's atmosphere during the Great Oxidation Event (GOE) approximately 2.3 billion years ago. This discovery may represent some of the earliest evidence of aerobic respiration on Earth.

Evolutionary Origins of a Key Oxygen-Using Enzyme

Published in the journal Palaeogeography, Palaeoclimatology, Palaeoecology, the study by MIT geobiologists traced the evolutionary origins of a key enzyme essential for aerobic respiration. This enzyme, found in most oxygen-breathing life forms today, was found to have evolved during the Mesoarchean period, between 3.2 and 2.8 billion years ago. This predates the Great Oxidation Event by several hundred million years.

Explaining Oxygen's Delayed Accumulation

The findings may help to address an unanswered question regarding why oxygen took a considerable time to accumulate in the atmosphere:

• Cyanobacteria, the first oxygen producers, emerged approximately 2.9 billion years ago, releasing oxygen through photosynthesis.
• Prior scientific theories suggested that geochemical reactions with rocks consumed a large portion of early oxygen.
• The new study proposes that biological consumption also played a role. Organisms evolving the oxygen-utilizing enzyme may have consumed small amounts of oxygen produced by nearby cyanobacteria.

This consumption could have delayed oxygen's atmospheric buildup for hundreds of millions of years.

Tracing the Enzyme: Research Methodology

The MIT team, including study co-authors Fatima Husain and Gregory Fournier, focused on heme-copper oxygen reductases, a set of enzymes critical for aerobic respiration. Their research methodology involved the following steps:

• Researchers identified the enzyme's genetic sequence.
• They searched databases containing millions of species' genomes for this sequence.
• The sequences were mapped onto an evolutionary tree of life, using fossil records to date the emergence and branching of species.

This methodology allowed the team to trace the enzyme's evolution back to the Mesoarchean era.

The research indicates that shortly after cyanobacteria began producing oxygen, other life forms developed the enzyme to use that oxygen, impacting the pace of Earth's oxygenation.