Evidence for early life in Earth’s oldest hydrothermal vent precipitates

Although it is not known when or where life on Earth began, some of the earliest habitable environments may have been submarine-hydrothermal vents. Here we describe putative fossilized microorganisms that are at least 3,770 million and possibly 4,280 million years old in ferruginous sedimentary rocks, interpreted as seafloor-hydrothermal vent-related precipitates, from the Nuvvuagittuq belt in Quebec, Canada. These structures occur as micrometre-scale haematite tubes and filaments with morphologies and mineral assemblages similar to those of filamentous microorganisms from modern hydrothermal vent precipitates and analogous microfossils in younger rocks. The Nuvvuagittuq rocks contain isotopically light carbon in carbonate and carbonaceous material, which occurs as graphitic inclusions in diagenetic carbonate rosettes, apatite blades intergrown among carbonate rosettes and magnetite–haematite granules, and is associated with carbonate in direct contact with the putative microfossils. Collectively, these observations are consistent with an oxidized biomass and provide evidence for biological activity in submarine-hydrothermal environments more than 3,770 million years ago

The geology and geochemistry of the East African Orogen in Northeastern Mozambique

The geology of northeastern Mozambique has been remapped at 1:250 000 scale. Proterozoic rocks, which make up the bulk of the area, form a number of gneiss complexes defined on the basis of their lithologies, metamorphic grade, structures, tectonic relationships and ages. The gneiss complexes, which contain both ortho- and paragneisses, range from Palaeo- to Neoproterozoic in age, and were juxtaposed along tectonic contacts during the late Neoproterozoic to Cambrian Pan-African Orogeny. In this paper we describe the geological evolution of the terranes north of the Lurio Belt, a major tectonic boundary which separates the complexes described in this paper from the Nampula Complex to the south. The Marrupa, Nairoto and Meluco Complexes are dominated by orthogneisses of felsic to intermediate compositions. Granulitic rocks, including charnockites, are present in the Unango, M’Sawize, Xixano and Ocua Complexes (the last forms the centre of the Lurio Belt). The Neoproterozoic Geci and Txitonga Groups are dominated by metasupracrustal rocks at low metamorphic grades and have been tectonically juxtaposed with the Unango Complex. Geochemical data integrate and support a model of terrain assembly in northeast Mozambique, which is largely published and mainly derived from our new geochronological, lithostratigraphic and structural work. This model shows the contrast between the mainly felsic lower tectonostratigraphic levels (Unango, Marrupa, Nairoto and Meluco Complexes) and the significantly more juvenile overlying complexes (Xixano, Muaquia, M’Sawize, Lalamo and Montepuez Complexes), which were all assembled during the Cambrian Pan-African orogeny. The juxtaposed terranes were stitched by several suites of Cambrian late- to post-tectonic granitoids