Résumé / Abstract
We recently published a new method providing model ages for Archean kerogens and therefore allowing the syngeneticity of ancient organic materials and their host rock to be tested (http://advances.sciencemag.org/content/4/2/eaar2091). Organic matter, known to be efficient at preserving large quantities of noble gases, was identified as a new archive of ancient atmospheric noble gases. This method couples Raman spectroscopy and measurements of Xe isotopes in Archean kerogens, by static mass spectrometry. Because the isotopic composition of atmospheric Xe evolved through time by mass dependent fractionation (Avice et al., 2017), we suggest that the degree of mass fractionation of Xe isotopes relative to modern atmosphere can provide a time stamp for dating ancient kerogens and thus constraining the time window for the diversification of early life during the Archean eon. In this talk, I will present new Xe isotope data for kerogens isolated from 3.45 Gy- to 1.8 Gy-old cherts, some of them being rich in microfossils. Implications regarding our understanding of the composition and evolution of the Archean atmosphere, as well as the timing of life emergence on Earth, will be discussed.
Noble gases trapped in archean kerogens as a new tracer of atmospheric evolution and life diversification