Chemical analysis of some of the world’s oldest rocks, by an international team led by McGill University researchers, has provided the earliest record yet of Earth's atmosphere. The results show that the air 4 billion years ago was very similar to that more than a billion years later, when the atmosphere -- though it likely would have been lethal to oxygen-dependent humans -- supported a thriving microbial biosphere that ultimately gave rise to the diversity of life on Earth today.
The distinctive “fecal prints” of microbes potentially provide a record of how Earth and life have co-evolved over the past 3.5 billion years as the planet’s temperature, oxygen levels, and greenhouse gases have changed. But, despite more than 60 years of study, it has proved difficult, until now, to “read” much of the information contained in this record. Research from McGill University and Israel’s Weizmann Institute of Science, recently published in the Proceedings of the National Academy of Sciences (PNAS), sheds light on the mysterious digestive processes of microbes, opening the way towards a better understanding of how life and the planet have changed over time.
An analysis of sulfide ore deposits from one of the world’s richest base-metal mines confirms that oxygen levels were extremely low on Earth 2.7 billion years ago, but also shows that microbes were actively feeding on sulfate in the ocean and influencing seawater chemistry during that geological time period.