Microbes and bacteria were the first living organisms on Earth, and they can be preserved in Archean silica-rich rocks. One such outcrop from western Australia, dated to 3.5 billion years ago, may hold the oldest "microfossils."
However, their authenticity has been called into question, and it is possible the microbe-like features may have been formed by non-biological processes inside an ancient hydrothermal vent.
In a new study published in Geology, De Gregorio et al. have compared carbonaceous matter in this rock with that from the 1.9-billion-year-old Gunflint Formation, which contains textbook examples of microfossil features. They found striking similarities between the carbon bonding and nitrogen, sulfur, and phosphorus composition of both ancient carbonaceous materials.
This similarity suggests that biological processes may be responsible for the formation of the 3.5-billion-year-old carbonaceous matter, and that hydrothermal microorganisms existed at that time on Earth.
- Bradley T. De Gregorio, Thomas G. Sharp, George J. Flynn, Sue Wirick, and Richard L. Hervig. Biogenic origin for Earth's oldest putative microfossils. Geology, 2009; DOI: 10.1130/G25683A.1
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