Ancient geological materials are likely to be contaminated through geological times. Thus, establishing the syngeneity of the organic matter embedded in a mineral matrix is a crucial step in the study of very ancient rocks. This is particularly the case for Archean siliceous sedimentary rocks (cherts), which record the earliest traces of life. We used electron paramagnetic resonance (EPR) for a...

Recognizing whether a planet can support life is a primary goal of future exoplanet spectral characterization missions, but past research on habitability assessment has largely ignored the vastly different conditions that have existed in our planet's long habitable history. This study presents simulations of a habitable yet dramatically different phase of Earth's history, when the atmosphere co...

Hopanes and steranes found in Archean rocks have been presented as key evidence supporting the early rise of oxygenic photosynthesis and eukaryotes, but the syngeneity of these hydrocarbon biomarkers is controversial. To resolve this debate, we performed a multilaboratory study of new cores from the Pilbara Craton, Australia, that were drilled and sampled using unprecedented hydrocarbon-clean p...

The Core Zone of the Southeastern Churchill Province, northeastern Laurentia, is a composite of Paleoproterozoic lithotectonic domains assembled in the vise between obliquely colliding Archean Superior and North Atlantic cratons between ca. 1860 and 1810 Ma. Detailed geological and U–Pb geochronological studies of domains in the southern Core Zone highlight significant differences in Archean an...

Mass-independent sulfur isotope signatures are observed in Archean and early Paleoproterozoic sedimentary sulfate and sulfide minerals, and provide the most robust constraints on early atmospheric oxygen levels. Smaller mass-independent sulfur isotope anomalies are observed in ice cores and interpreted as a tracer of stratospheric volcanic loading. Photochemistry of sulfur dioxide (SO 2) has be...

The geochemical behaviors of Vand Sc during partial melting are more similar to each other than to most other elements but, in detail, the partitioning of V is redox-sensitive whereas that of Sc is not. The V/Sc ratio in basalts is shown here to be a sensitive and robust recorder of the oxygen fugacity (fO2) of their mantle source regions. The use of V/Sc ratios differs from the use of V and/or...

Komatiites (ultramafic volcanic rocks) are common among Archean terrains, but rare or absent among rocks< 2.8 Ga old, which implies that the Archean upper mantle was fundamentally different from the modem one. The magma( s) parental to a certain group of lunar samples appear to have formed by exceptionally high-degree partial melting, like the magmas parental to komatiites: The Mg-rich suite of...

Xenon (Xe) is an exceptional tracer for investigating the origin and fate of volatile elements on Earth. The initial isotopic composition of atmospheric Xe remains unknown, as do the mechanisms involved in its depletion and isotopic fractionation compared with other reservoirs in the solar system. Here we present high precision analyses of noble gases trapped in fluid inclusions of Archean quar...

From iodine-plutonium-xenon isotope systematics, we re-evaluate time constraints on the early evolution of the Earth-atmosphere system and, by inference, on the Moon-forming event. Two extinct radioactivites (I, T1/2 = 15.6 Ma, and Pu, T1/2 = 80 Ma) have produced radiogenic Xe and fissiogenic Xe, respectively, within the Earth, which related isotope fingerprints are seen in the compositions of ...

Some time ago Buick (1984) cast doubt on both the biogenicity and the age of the objects we described as Early Archean bacterial microfossils in a previous paper (Awramik et al., 1983). He presented new evidence significant to the interpretation of these objects, but his report also contains statements that may be misleading. We wish to comment on his new evidence and to correct the misleading ...