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The Great Unconformity, a profound gap in Earth's stratigraphic record often evident below the base of the Cambrian system, has remained among the most enigmatic field observations in Earth science for over a century. While long associated directly or indirectly with the occurrence of the earliest complex animal fossils, a conclusive explanation for the formation and global extent of the Great Unconformity has remained elusive. Here we show that the Great Unconformity is associated with a set of large global oxygen and hafnium isotope excursions in magmatic zircon that suggest a late Neoproterozoic crustal erosion and sediment subduction event of unprecedented scale. These excursions, the Great Unconformity, preservational irregularities in the terrestrial bolide impact record, and the first-order pattern of Phanerozoic sedimentation can together be explained by spatially heterogeneous Neoproterozoic glacial erosion totaling a global average of 3-5 vertical kilometers, along with the subsequent thermal and isostatic consequences of this erosion for global continental freeboard.

Precambrian paleomagnetic studies are critical for testing paleogeographic reconstructions in deep time but rely on the fidelity of the assumption of the geocentric axial dipole (GAD) hypothesis. With high‐reliability data from mafic dykes and volcanic rocks, the scatter of individual virtual geomagnetic poles (VGPs) can be used to test simple GAD models. In order to conduct such a test, the VGPs must be adequate in number and in spatial coverage of the sampling sites. In this study, we targeted the 2.1 Ga Indin dyke swarm of the Slave craton. Building on previous sampling of the Indin dyke swarm in the western and central parts of southern Slave craton, we report results from 9 additional sites in the central and eastern parts of the craton, sites that significantly expand the width of the dyke swarm across the entire craton. The VGPs obtained from 7 of 9 newly identified Indin dykes are broadly similar to previously reported directions, expanding the total of VGPs for individual Indin dykes to n = 28, which is sufficient for a test of the GAD‐based statistical models using VGP scatter. The high VGP scatter of the Indin swarm can be attributed to the relatively high paleolatitude of 56° ± 6° for the Slave craton at the time of dyke emplacement. The Indin data have VGP scatter that is consistent with field models associated with the GAD hypothesis for the indicated paleolatitude, thus confirming the fidelity of the GAD field at ca. 2.1 Ga. Plain Language Summary: A fundamental assumption in paleomagnetism is the geocentric axial dipole (GAD) hypothesis. One feature of GAD that can be used to test it is that paleosecular variation (PSV) under a GAD field varies systematically with latitude, with its scatter being greater at relatively high latitudes than at low latitudes. Lavas and dykes for the past five million years and for various points in Earth's history generally support GAD, but there are some large gaps between these tests. Short‐term departures from GAD and/or intervals of weak fields have been suggested for certain time periods, highlighting the importance of regular tests of the GAD field throughout geological time. We study the ca. 2.1‐billion‐year‐old Indin dykes that fills one of these critical gaps. The Indin dyke swarm intruded across a large swath of the southern Slave craton, allowing us to extensively sample PSV. Our study finds a large VGP scatter for the Indin dykes, but as is to be expected given the relatively high paleolatitude. Thus, the scatter of Indin VGPs aligns with the GAD field model, confirming the reliability of the GAD field at ca. 2.1 Ga. Future studies of paleogeographic reconstruction during this period can confidently utilize paleomagnetism as a reliable quantitative constraint. Key Points: The ca. 2.1 Ga Indin dyke swarm has now been extensively sampled across much of the southern Slave cratonThe age and relatively high paleolatitude of the Indin dyke swarm provides an important constraint on the ancient magnetic fieldThe scatter of the paleomagnetic directions of the Indin dykes statistically supports a typical geomagnetic dipole field at 2.1 Ga [ABSTRACT FROM AUTHOR]

In a deforming partially molten rock, melt concentrates into a grain‐scale melt pocket aligned at a preferred orientation (melt‐preferred orientation, or MPO). However, observing this texture alone provides limited information on the 3D orientation and geometry of these melt pockets, which are critical parameters for estimating permeability. Here, we modeled the MPO of experimentally deformed peridotites by simulating melt streaks arising from melt pockets of various shapes and 3D orientations. The model aims to identify 3D distribution and characteristics of melt pockets that could account for the observed length, thickness, and the probability of melt streaks. Results show that melt pockets at preferred orientation exhibit greater length, thickness, and number density compared to those perpendicular. These results can be incorporated into the simulation of melt flow through individual melt pockets, which allows us to estimate the permeability corresponding to the observed MPO. We found that the permeability of vertically compressed peridotites increases with increasing compressive strain and a more elongated and thickened shape for melt pocket aligned at preferred orientation. The vertical permeability in the sample with 30% compressive strain is at least 40 times larger than that of an undeformed sample. For peridotites deformed under simple shear, the permeability exhibits an anisotropy of at least three. Such anisotropic permeability, coupled with the formation of melt‐rich bands and other melt channels, is believed to cause lateral melt focusing beneath mid‐ocean ridges. Plain Language Summary: The distribution of melt at the grain scale controls the permeability in partially molten rock. While observe melt streaks on thin sections show variations in length and thickness with respect to the orientation, the geometry and distribution of melt pockets in 3D are poorly constrained. Here, we use an improved statistical model to identify the dependence of melt pocket dimensions as functions of orientation. We further calculate melt flux through individual melt streaks and estimate permeability corresponding to the observed melt distribution texture. We found that deformation in the mantle can significantly accelerate melt extraction and potentially bend the melt flow using anisotropic permeability. Key Points: We parameterized the 3D shapes and orientations of melt pockets under the constraints of observed melt‐preferred orientation (MPO)Permeability in peridotites deformed under vertical compression increases with compressive strain and demonstrates anisotropy up to twoPermeability in peridotites deformed under simple shear demonstrates anisotropy of at least three [ABSTRACT FROM AUTHOR]

Due to the scarcity of rock samples, the Hadean Era predating 4 billion years ago (Ga) poses challenges in understanding geological processes like subaerial weathering and plate tectonics that are critical for the evolution of life. The Jack Hills zircon from Western Australia, the primary Hadean samples available, offer valuable insights into magma sources and tectonic genesis through trace element signatures. However, a consensus on these signatures has not been reached. To address this, we developed a machine learning classifier capable of deciphering the geochemical fingerprints of zircon. This allowed us to identify the oldest detrital zircon originating from sedimentary-derived "S-type" granites. Our results indicate the presence of S-type granites as early as 4.24 Ga, persisting throughout the Hadean into the Archean. Examining global detrital zircon across Earth's history reveals consistent supercontinent-like cycles from the present back to the Hadean. These findings suggest that a significant amount of Hadean continental crust was exposed, weathered into sediments, and incorporated into the magma sources of Jack Hills zircon. Only the early operation of both subaerial weathering and plate subduction can account for the prevalence of S-type granites we observe. Additionally, the periodic evolution of S-type granite proportions implies that subduction-driven tectonic cycles were active during the Hadean, at least around 4.2 Ga. The evidence thus points toward an early Earth resembling the modern Earth in terms of active tectonics and habitable surface conditions. This suggests the potential for life to originate in environments like warm ponds rather than extreme hydrothermal settings. [ABSTRACT FROM AUTHOR]