A new study published in National Science Review reveals that the asthenosphere plays an active role, rather than being passively involved as previously expected, in modulating seafloor spreading at mid-ocean ridges. The research, led by Prof. Chuan-Zhou Liu of the Laoshan Laboratory, shows that the change in seafloor spreading mode at the 23°N Mid-Atlantic Ridge was controlled by the compositional variations in the upwelling asthenosphere. The hot mantle beneath ocean ridges gives rise to ocean crust through decompressional melting. This finding reinforces the idea that compositional heterogeneity of the asthenosphere can exert a controlling role over the spreading mode through modulating the magma flux at ocean ridges.

A digital reconstruction of the nearly one-million-year-old Yunxian 2 cranium from China, which corrected previous distortions inherent in the fossil, suggests it belonged to the Asian Homo longi clade. This means the cranium represents an early branch of the sister lineage to modern humans that may have included the enigmatic Denisovans. Fossil evidence shows that, during the Middle Pleistocene, multiple Homo lineages with diverse physical forms coexisted. Much of what is known about human evolution and archaic hominins relies on fossil skulls. Yet many specimens from this era are damaged and/or deformed, leading to uncertainties concerning species interpretations. For example, the Yunxian crania from China date back nearly a million years and exhibit a mosaic of primitive traits resembling Homo erectus alongside features suggestive of later species, such as Homo sapiens. However, because one of these skulls, Yunxian 2, was highly distorted, its evolutionary position has long been uncertain. Using advanced CT scanning and digital reconstruction techniques, Xiaobo Feng and colleagues corrected the compression and distortions in the Yunxian 2 crania. According to Feng et al., phylogenetic analyses incorporating the reconstructed Yunxian 2 crania revealed a mix of previously unknown primitive and derived traits, suggesting that the fossil belongs to the Asian H.  longi clade – a sister group to Homo sapiens, which likely included the Denisovans. Individuals within the H. longi clade exhibit distinctive traits, including a larger braincase, narrower spacing between the eyes, a more pronounced glabellar depression, and a lower, elongated frontal bone, which are characteristics clearly visible in the Yunxian 2 fossil. The authors also show that Yunxian fossils are likely the oldest within the longi clade, though not the most basal. Given the fossil’s blend of primitive traits from earlier humans and more derived features shared with H. longi and H. sapiens, Feng et al. suggest that the Yunxian group may represent a transitional form, capturing an early phase of rapid diversification within these lineages.

The American Geophysical Union (AGU) and the American Meteorological Society (AMS) invite contribution proposals for a joint special collection of research articles called the “U.S. Climate Collection: Informing Assessment of Risks and Solutions.”  This is the next step in the collaborative effort announced earlier this year in the wake of the dismissal of the Sixth National Climate Assessment (NCA) authors.