ALBERT

Description: The greatest ice ages in Earth’s history occurred during the 654–635 Ma Marinoan glaciation, when glaciers reached tropical oceans and our planet approached a snowball Earth condition. Paleontological and genomic data suggest that several eukaryotic groups must have survived the Marinoan glaciation. But their fossil record is scarce and limited to microbes, whose ecological and physiological ranges are poorly constrained, thus hampering a full understanding of how and where eukaryotic life—particularly macroscopic phototrophs—survived this snowball Earth. Here we report carbonaceous compression fossils from the Marinoan-age Nantuo Formation in South China. These fossils are preserved in thin black shales sandwiched between glacial diamictites deposited in inner shelf environments of the mid-latitudinal Yangtze block. Some of these fossils are interpreted as benthic macroalgae. Thus, the Marinoan glaciation must have been punctuated by episodes of open waters where habitable benthic substrates were available in the photic zone and along the coast of mid-latitudinal continents. Such open waters may have been the refugia where macroscopic phototrophs survived the Marinoan glaciation and subsequently diversified in the early Ediacaran Period.

Description: Asian monsoon records are widely documented, but specific proxies of monsoonal rainfall are limited. We present here two new independent proxy records from peatland and stalagmite archives that indicate a high degree of concordance between monsoon-driven hydrological changes occurring since the last deglaciation in a broad region of central China. The wet periods elevated the water table in the Dajiuhu peatland, as recorded by reduced mass accumulation rates of hopanoids, biomarkers for aerobic microbes, confirmed by molecular phylogenic analyses. The hopanoid-based reconstruction is supported by the first report of the environmental magnetism parameter ARM/SIRM (anhysteretic remanent magnetization / saturation isothermal remanent magnetization; ratio of fine magnetic particles to total ferrimagnetic particles) in a stalagmite from Heshang Cave in central China. Heavy rainfall resulted in the enhanced transport of coarse particles to the cave and thus low ARM/SIRM values in the stalagmite. The hydrological conditions inferred from the two records reveal three relatively long wet periods in central China: 13–11.5 k.y. ago, 9.5–7.0 k.y. ago, and 3.0–1.5 k.y. ago. Archaeological evidence for the hydrological impacts on regional populations comes from the observation that temporal shifts among six distinctive cultures of the Neolithic Period to the Iron Age in central China occurred during wet periods or flood episodes. Spatiotemporal distributions of 〉1600 prehistoric settlement sites correlate with the proxy-inferred fluctuating hydrological conditions, with enhanced flooding risk forcing major relocations of human settlements away from riparian zones.