Chemical analysis of some of the world’s oldest rocks 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.
In the new study, a team led by researchers from McGill’s Earth and Planetary Sciences Department, used mass spectrometry to measure the amounts of different isotopes of sulfur in rocks from the Nuvvuagittuq belt. The results enabled the scientists to determine that the sulfur in these rocks, which are at least 3.8 billion years old and possibly 500 million years older, had been cycled through Earth’s early atmosphere, showing the air at the time was extremely oxygen-poor compared to today, and may have had more methane and carbon dioxide.
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