Many aspects of Earth's early sulfur cycle, from the origin of mass-anomalous fractionations to the degree of biological participation, remain poorly understood--in part due to complications from postdepositional diagenetic and metamorphic processes. Using a combination of scanning high-resolution magnetic superconducting quantum interference device (SQUID) microscopy and secondary ion mass spe...

[1] For more than four decades, scientists have been trying to find an answer to one of the most fundamental questions in paleoclimatology, the “faint young Sun problem.” For the early Earth, models of stellar evolution predict a solar energy input to the climate system that is about 25% lower than today. This would result in a completely frozen world over the first 2 billion years in the histo...

Editor: T.M. Harrison Non-arc basalts of Archean and Proterozoic age have model primary magmas that exhibit mantle potential temperatures TP that increase from 1350 °C at the present to a maximum of ∼1500–1600 °C at 2.5–3.0 Ga. The overall trend of these temperatures converges smoothly to that of the present-day MORB source, supporting the interpretation that the non-arc basalts formed by the m...

S U M M A R Y Rayleigh wave phase velocity maps in southern Africa are obtained at periods from 6 to 40 s using seismic ambient noise tomography applied to data from the Southern Africa Seismic Experiment (SASE) deployed between 1997 and 1999. These phase velocity maps are combined with those from 45 to 143 s period which were determined previously using a two-planewave method by Li & Burke. In...

Considerable discussion surrounds the potential role of anoxygenic phototrophic Fe(II)-oxidizing bacteria in both the genesis of Banded Iron Formations (BIFs) and early marine productivity. However, anoxygenic phototrophs have yet to be identified in modern environments with comparable chemistry and physical structure to the ancient Fe(II)-rich (ferruginous) oceans from which BIFs deposited. La...

We agree with Glikson [1] that the identification of Precambrian impact deposits is an important and largely unresolved problem, and thank him for providing us with an opportunity to further discuss our mineralogical and geochemical results [2] on the enigmatic spherule layers in the Barberton Mountain Land of South Africa. We note, however, that unfortunately Glikson has not been able to name ...

Determining the composition of Archean atmosphere and oceans is vital to understanding environmental conditions that existed on surface early Earth. The analysis atmospheric remnants in fluid inclusions trapped Archean-aged samples has shown Xe isotopic signature progressively evolved via mass-dependent fractionation, arriving at a modern around Archean-Proterozoic transition. mechanisms drivin...