The rise and fall of Archean atmospheric oxygen - Did temporary carbon burial as Fe(ox)-DOM complexes play a modulating role?

获取分子氧仍然被认为是地球上日益复杂的生命进化的主要驱动力。在这方面，含氧光合作用的出现和随后的大氧化事件（GOE）代表了地球历史上的两个关键事件。然而，关于大气中氧气持续上升的细节仍然很少。例如，我们知道，在GOE期间，大气中O2的最初大幅上升，紧接着又出现了新的下降。直到很久以后，在新元古代，大气中的氧含量才再次上升——这一次稳定到了接近现代的水平。是什么导致了最初的超调和再次回落？在含氧光合作用中释放的氧化力在化学计量上与从二氧化碳中固定到生物质中的碳量相对应。生物量的再矿化导致氧气的再次减少，因此，如果没有碳埋藏和地壳碳储层的初步建立，地球早期大气的氧化是不可能的。一旦生物物质到达沉积物，它就会逐渐转化为稳定的干酪根，并且通常被锁定在碳循环的地质部分，时间尺度为10 ~ 10^6年。但对于更不稳定的碳埋藏形式来说，情况可能会大不相同。我们知道，太古宙海相溶解有机质（DOM）池的规模一定比现在大得多，太古宙时期沉积了大量的带状铁地层（BIF）。bif前驱体矿物水合铁容易吸附大量DOM，但由于其稳定性较低，在变态的早期阶段就已经发生再结晶。在这个项目中，我们将测试一个假设，即dom -铁水合物可能暂时掩埋了足够的有机物，从而导致大气中氧气的大幅增加。与沉积干酪根相比，DOM的地质命运几乎一无所知。存在的可能性是，在早期变质作用中，铁水合石在再结晶过程中从未成熟的BIF沉积物中丢失。释放DOM的异养重组随后会下调先前释放的氧。我们将构建水合铁和纯蓝藻DOM的配合物，并在高压灭菌器中模拟区域变质作用，以揭示在变质作用和早期变质作用地质条件下DOM的稳定性和行为。最终，我们将评估biff中临时碳储存作为太古宙大气氧水平调制器的可能性——无论是超调还是重新下降——从而从本质上评估构造对氧的持续上升和生物复杂性进化的控制的可能性。

Access to molecular oxygen is still considered the primary driver for the evolution of increasingly complex life on Earth. In this respect the emergence of oxygenic photosynthesis, and the subsequent Great Oxidation Event (GOE) represent two pivotal incidents in Earth history. Details of the protracted rise of atmospheric oxygen are however still sparse. For example, we know that the initial, substantial rise of atmospheric O2 during the GOE was immediately followed by a renewed drawdown. Only much later, during the Neoproterozoic, did a renewed rise of atmospheric O2 occur - this time to stable near-modern levels. What caused the initial overshoot and renewed drawdown? The oxidizing power released during oxygenic photosynthesis corresponds stoichiometrically to the amount of carbon that is fixed into biomass from CO2. Remineralization of the biomass causes renewed O2 drawdown and hence the oxidation of Earth’s early atmosphere would not have been possible without carbon burial and the initial establishment of a crustal carbon reservoir. Once biomass reaches the sediment it is gradually converted to stable kerogen, and typically locked up in the geological portion of the carbon cycle on time scales >10^6 years. But this could have been very different for more labile forms of buried carbon. We know that the Archean marine pool of dissolved organic matter (DOM) must have been magnitudes larger than at present, and that enormous volumes of banded iron formations (BIF) were deposited during the Archean. The BIF-precursor mineral ferrihydrite is prone to adsorbing large amounts of DOM, but due to a low stability it tends to recrystallize already during earliest stages of metamorphosis. In this project we will test the hypothesis that DOM-ferrihydrite complexes could have temporarily buried sufficient organic matter to cause a substantial rise in atmospheric oxygen. In contrast to sedimentary kerogen, virtually nothing is known about the geological fate of DOM. The possibility exists that it would have been lost from immature BIF sediments upon recrystallization of the ferrihydrite during earliest metamorphism. Heterotrophic reworking of the released DOM would subsequently down-regulate the previously released oxygen. We will create complexes of ferrihydrite and pure cyanobacterial DOM, which will be subjected to simulated regional metamorphism in an autoclave to reveal the stability and behavior of DOM under geological conditions of catagenesis and early metamorphism. Eventually we will evaluate the possibility of temporary carbon storage in BIFs as a modulator for Archean atmospheric oxygen levels - both the overshoot and the renewed drawdown - thereby essentially evaluating the likelihood of tectonic control on the protracted rise of oxygen and the evolution of organismic complexity.