#vindhyan

Fossil oxygen bubbles, 1.6 billion years old

Back in the early days of life on Earth the largest organisms were microbial mats organised a bit like cities, with each microbe feeding off the residues of the next up the trophic chain. These formed layered columnar structures known as stromatolites (see http://bit.ly/2ps2qu9, http://bit.ly/2FRacbR and http://bit.ly/1OCAiuq) that have been part of the fossil record for some 3 billion years and remain alive in high salinity lagoon environments today. At the bottom of a shallow sea back in the mid Proterozoic, some of these were fossilised in fine enough detail to reveal these trapped oxygen bubbles as the next layer of sediment overgrew the living layer of bacteria and froze the gas that the photosynthetic cyanobacteria had just produced into the rock record forever. Most of the bubbles were spherical but a few were compressed, revealing sedimentary events that happened way back in Deep Time. Some also have bacterial filaments wending around them.

The rocks are phosphate rich, and come from the Vindhyan Supergroup found in central India, dating from roughly the period where our eukaryotic cells first evolved from a symbiosis between an alpha proteobacteria that invaded and made its home in a methanogen. They represent a relic of the Great Oxygenation Event that was drawing to its close (it ran from around 2.5-1.6 billion years ago), in which life altered the biogeochemistry of our planet forever, paving the way for the evolution of complex organisms using aerobic respiration, and a considerable dose of mineral evolution as well (see http://bit.ly/2m0Bujs).

Loz Image credit: Stefan Bengtson.

http://bit.ly/2G7ixY8 http://bit.ly/2prK10p http://bit.ly/2HRIU1Q http://bit.ly/2u0R99K http://bit.ly/2tfhbFK