Effect of a giant meteorite impact on Paleoarchean surface environments and life.

Large meteorite impacts must have strongly affected the habitability of the early Earth. Rocks of the Archean Eon record at least 16 major impact events, involving bolides larger than 10 km in diameter. These impacts probably had severe, albeit temporary, consequences for surface environments.

Origin of Silicate Spherules and Geochemistry of Re and Platinum-Group Elements Within Microfossil-Bearing Archean Chert from the 3.4 Ga Strelley Pool Formation, Western Australia.

Silicate spherules have been identified from the ca. 3.4 Ga-old Strelley Pool Formation (SPF) in the Pilbara Craton, Western Australia.

Heterogeneous Hadean crust with ambient mantle affinity recorded in detrital zircons of the Green Sandstone Bed, South Africa.

The nature of Earth's earliest crust and the processes by which it formed remain major issues in Precambrian geology. Due to the absence of a rock record older than ∼4.02 Ga, the only direct record of the Hadean is from rare detrital zircon and that largely from a single area: the Jack Hills and Mount Narryer region of Western Australia.

Deposition of >3.7 Ga clay-rich strata of the Mawrth Vallis Group, Mars, in lacustrine, alluvial, and aeolian environments.

The presence of abundant phyllosilicate minerals in Noachian (>3.7 Ga) rocks on Mars has been taken as evidence that liquid water was stable at or near the surface early in martian history. This study investigates some of these clay-rich strata exposed in crater rim and inverted terrain settings in the Mawrth Vallis region of Mars.

Photosynthetic microbial mats in the 3,416-Myr-old ocean.

Recent re-evaluations of the geological record of the earliest life on Earth have led to the suggestion that some of the oldest putative microfossils and carbonaceous matter were formed through abiotic hydrothermal processes. Similarly, many early Archaean (more than 3,400-Myr-old) cherts have been reinterpreted as hydrothermal deposits rather than products of normal marine sedimentary processes. Here we present the results of a field, petrographic and geochemical study testing these hypotheses for the 3,416-Myr-old Buck Reef Chert, South Africa.

A lower limit for atmospheric carbon dioxide levels 3.2 billion years ago.

The quantification of greenhouse gases present in the Archaean atmosphere is critical for understanding the evolution of atmospheric oxygen, surface temperatures and the conditions for life on early Earth. For instance, it has been argued that small changes in the balance between two potential greenhouse gases, carbon dioxide and methane, may have dictated the feedback cycle involving organic haze production and global cooling. Climate models have focused on carbon dioxide as the greenhouse gas responsible for maintaining above-freezing surface temperatures during a time of low solar luminosity.

Spherule beds 3.47-3.24 billion years old in the Barberton Greenstone Belt, South Africa: a record of large meteorite impacts and their influence on early crustal and biological evolution.

Four layers, S1-S4, containing sand-sized spherical particles formed as a result of large meteorite impacts, occur in 3.47-3.24 Ga rocks of the Barberton Greenstone Belt, South Africa.

Molecular identification of cyanobacteria associated with stromatolites from distinct geographical locations.

Modern stromatolites represent a significant resource for studying microbial ecology and evolution. A preliminary investigation was undertaken employing specific genetic probes to characterize the cyanobacteria responsible for stromatolite construction in a range of environments, including microbial mats found in Australia not previously examined with molecular methods. Isolates of cyanobacteria were collected from stromatolites in thermal springs, hypersaline lakes, and oceanic fringes on two continents.

An archean impact layer from the Pilbara and Kaapvaal cratons.

The Barberton greenstone belt of South Africa and the eastern Pilbara block of Western Australia provide information about Earth's surface environments between 3.2 and 3.5 billion years ago, including evidence for four large bolide impacts that likely created large craters, deformed the target rocks, and altered the environment.