Rock salt traces the Great Oxygenation Event Between 2.5 and 1.6 billion years ago the amount of oxy

Rock salt traces the Great Oxygenation EventBetween 2.5 and 1.6 billion years ago the amount of oxygen in our planet’s air rose in stages (with a third burst in the late Precambrian which some have linked to the evolution of complex shell secreting life) as photosynthetic cyanobacteria slowly exuded it into the sea and air in a period known by the capitalised label in the title (see https://bit.ly/2EgOWqc, https://bit.ly/1d4DqjU and https://bit.ly/2EhpWPF). At first it was soaked up by the reduced (see https://bit.ly/1I4XWKt) iron in the water, and precipitated out as rocks known as BIFs, for banded iron formation (see https://bit.ly/1OCAiuq, https://bit.ly/2qdTpFa and https://bit.ly/2uWo9A7), before gradually rising in the atmosphere. This of course paved the way for the spread of life forms that use the more energetic aerobic pathway of respiration (such as us) and for the evolution of minerals such as oxides and carbonates in a process of coevolution of rocks and life (see https://bit.ly/2m0bUJS).New clues to this epoch have emerged from a drill core, extracted from nearly 2km down in Karelia in north western Russia. It brought up 600 metres of evaporite rocks that had precipitated when a 2.3 billion year sea repeatedly dried up, and is therefore made of a mixture of salts, including table salt (aka halite or sodium chloride, see https://bit.ly/2uWquLp and https://bit.ly/2uWquLp) and calcium sulphate. Within these salts are trapped gas bubbles, which the research team analysed to see what they could tell us about the levels of oxygen, both in the ancient atmosphere and dissolved in the long gone seas from which the salts formed. Sulphates in the rock also serve as a proxy for atmospheric oxygen, since it results from the weathering of pyrite and the washing of the result into the sea by rivers.The first surprise was that the rise at this early stage of oxygenation proved to be much more than had been thought. The amount of sulphate present indicated that the amount dissolved in the ancient sea was at least 30% that of modern levels, which will require a rethink of what constraints, were imposed by the environment on the world’s burgeoning life forms. It also indicates that net oxygen production was roaring ahead that long ago, implying that the spread of oxidation around the globe’s surface environments may have been more rapid than thought. The overall geochemistry also implies the GOE was a rapid event, geologically speaking, rather than a slow one.What remains unknown is whether the cause is linked to increased photosynthesis or a change in biogeochemical cycles that allowed oxygen to accumulate quickly. This salt is a billion years older than the previous record holder, making it a unique record of long gone times,. Such units often dissolve later in geological time, or extrude out to the surface as diapirs making this unit a unique record of a long gone near unimaginable past, since it has given us our first direct quantitative evidence of the direct chemistry of air and ocean in a period about which little is known.LozImage credit: Aivo Lepland/Geological Survey of Norwayhttps://bit.ly/2q0vcCchttps://bit.ly/2Gx62T3https://to.pbs.org/2q12VvwOriginal paper, paywall access: https://bit.ly/2H3Wuji__ -- source link

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