According to a study published in the journal Earth and Planetary Science Letters, oxygen-producing life-forms appeared hundreds of millions of years earlier than was previously estimated.
Researchers report that oxygen made its presence felt on Earth for the first time about 3.2 billion years ago based on the discovery of rusty rock layers rich in iron within sediments deposited over shallow ocean floors. Analyzing the rock layers showed that the ancient rust was biological, placing the first oxygen producers some 200 million years earlier than earlier estimates.
Today, plants are credited for producing oxygen but it was cyanobacteria that started the effort billions of years ago by developing the earliest versions of photosynthesis. As more and more oxygen was produced, complex, multicellular life started to develop and thrive. Geologists refer to this event as the "Great Oxygenation" and believe it was a major turning point for life on the planet.
For the study, Aaron Satkoski and colleagues analyzed the Manzimnyama Banded Iron Formation, a sequence of pink- and red-striped rocks from South Africa that's 3.2 billion years old. First deposited in the early seas, the rocks are of that color because they contain iron that rusted away when exposed to oxygen. By looking at the ratio of iron isotopes Fe-54 and Fe-56, the researchers discovered that the rocks formed with a 0.1-percent oxygen concentration.
This level of oxygen doesn't sound like a lot but it is significant in that majority of rocks from the period had zero oxygen content. It was further proven that oxygen was indeed present when uranium atoms are observed to be not in their usual crystalline form as a result of reacting to oxygen.
The study was only able to identify the presence of oxygen in one location so it is still possible that cyanobacteria could have been thriving around the world even earlier or that they were present in other parts of the globe. However, if there were truly more cyanobacteria than what the study hints at, it doesn't explain why the Great Oxygenation needed another billion years to unfold.
A possible explanation is that cyanobacteria may have been present in other areas but were in limited number given the harsh living conditions in the planet billions of years ago. Early Earth was practically unlivable so it's not surprising that cyanobacteria bid their time, making the most out of resources they could access.
Photo: NOAA/NASA GOES Project | Flickr
