Oldest fossils detected by Raman imaging
When did life on Earth begin?
Based on new Raman data from microfossils, scientists have dated the origin of life to at least 3,77 billion years ago.
Bubbling submarine-hydrothermal vents are believed to be the places where life on Earth emerged. Whether that happened 3.5 or 3.7 billion years ago or even further into the past is subject of intense discussion in the scientific community. Why? Because it is hard to determine whether or not chemical traces in very old sedimentary rocks– so called microfossils – are metamorphosed products of biological organisms. Dominic Papineau, a geologist who has long followed the tracks of early life, and PhD student Mark Dodd, both from University College London (UK), along with colleagues used a microscopic approach to look for the answer. With optical microscopy they imaged thin sections from fragments found in the Nuvvuagittuq Supracrustal Belt (NSB) in Canada that once belonged to a very early oceanic crust. They identified 50 – 200 μm rosette-like structures.
Through chemical imaging performed with a WITec alpha300R confocal Raman microscope, the scientists could identify the compounds – calcite, haematite, quartz, magnetite and apatite - therein and their spatial distribution. Modern iron-oxidizing bacteria living in hot vents can form Fe-containing filaments and tubes. For that reason scientists believe that similar structures in much older rocks indicated biogenic origin. Similar structures found in Løkken jasper in Norway that geologically is somewhat younger than the NSB had already been attributed to mineralized bacteria. So the authors of the current study suggested that the carbonate rosettes they had seen are also of biogenic origin. They concluded: “Preservation in the NSV of carbonaceous material and minerals in diagenetic rosettes and granules that formed from the oxidation of biomass, together with the presence of tubes similar in mineralogy and morphology to those in younger jaspers interpreted as microfossils, reveal that life established a habitat near submarine-hydrothermal vents before 3,770 Myr ago and possibly as early as 4,290 Myr ago”.
Dominic Papineau wrote: “We used the WITec micro-Raman to map, down to sub-micron scales, the minerals associated with the oldest microfossils on Earth. This was vital to the discovery of key structures like rosettes, granules as well as minerals associated with the filamentous microfossils such as micron-size apatite, carbonate, and graphitic carbon, all of which point to the metamorphosed mineralised product of decayed microbial organic matter.”