Month: September 2022

‪“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.”‬" "‪https://lnkd.in/d5waTiU View in LinkedIn

MASSIVE LOSS. “In either a constructive or a destructive endmember scenario, if global sediment supply from tectonic uplift is held constant near Phanerozoic levels, then the depressed Proterozoic sediment volume in Fig. 1A suggests that on the order of 109km3 of sediment are absent from the continental crust and deposited instead in the deep ocean basins—either gradually, throughout the Proterozoic due to a diminished sediment storage capacity of the continents in a constructive model, or rapidly during an interval of enhanced erosion near the Proterozoic–Phanerozoic boundary in a destructive model.” https://lnkd.in/d6fatHN View in LinkedIn

TECTONICS. “Before the plate tectonic revolution, the missing sediments from Walcott’s “Lipalian interval” were generally expected to reside in the ocean basins; their absence, along with the young age of the ocean crust, was considered a significant point of evidence in favor of seafloor spreading and plate tectonics. In a plate tectonic model, much sediment accumulated on the oceanic crust is consumed by subduction—presently at a rate of about 1.65 km3/y. Due to its low density and fusibility, however, subducted sediment in the mantle wedge is often incorporated into new arc magmas; consequently, a chemical or isotopic signature of subducted sediment (if sufficiently voluminous) may be preserved within the igneous record.” https://lnkd.in/d6fatHN View in LinkedIn

MASSIVE UNDERSTATEMENT. “We conclude that the Phanerozoic sedimentary record is best explained by a Great Unconformity of inherently coupled erosive and constructive genesis, with Neoproterozoic glacial erosion governing the subsequent history of continental freeboard and sediment accumulation. As such, the environmental and geochemical changes that led to the diversification of multicellular animals may be considered a direct consequence of Neoproterozoic glaciation.” https://lnkd.in/d6fatHN View in LinkedIn

BOATLOAD OF EROSION. “Their evidence implies a culprit behind all of the missing rock: global tectonic uplift associated with the breakup of the ancient supercontinent Rodinia. This means there was probably a boatload of erosion. The timing of the GU’s formation may also help explain what triggered the so-called “snowball Earth” glaciations, an episode beginning about 720 million years ago in which much of the planet likely became covered in ice sheets.’ https://lnkd.in/ddDSSXe View in LinkedIn

GLACIAL TRIGGER. “Chemical weathering associated with the erosion that formed the Great Unconformity likely pulled the greenhouse gas carbon dioxide out of the atmosphere, sequestering vast quantities in the ocean and lithosphere. This “primed the pump for the glaciations.” https://lnkd.in/ddDSSXe View in LinkedIn

IGNORED HYPOTHESIS. “Though I’ve read numerous articles struggling to explain away the Cambrian explosion, I’d never heard of anyone arguing that the alleged Precambrian ancestors to the Cambrian animals were missing because the strata containing their fossils had been completely eroded from the face of the earth in such a “Great Unconformity.” But after hearing this objection, I did some research. I discovered a single place where this argument has been made: It was over 100 years ago by Charles Doolittle Walcott, the famous geologist who discovered the Burgess Shale. Apparently the argument was never adopted by subsequent geologists, for good reasons.” https://lnkd.in/dF5HJJK View in LinkedIn

GRADUAL ACCEPTANCE. “Effectively, in many locations, Earth buried the evidence of about a fifth of its geological history, the team argues today in the Proceedings of the National Academy of Sciences. The notion is elegant but provocative, and the authors themselves predict that some geoscientists will express skepticism. The idea that Earth was a giant frigid “snowball” around 700 million years ago is being increasingly accepted by the scientific community.” https://lnkd.in/dDSckgW View in LinkedIn

CONFLUENCE OF FACTORS. “If validated, the implications of this story could be enormously significant. After all, this study points out that complex life first emerged when Snowball Earth’s monstrous mealtime came to an end. Glaciers would have carved out fjord-like shallow marine areas, which could have been havens for life as the planet warmed back up. This colossal crustal consumption may have also coincided with major geochemical and environmental changes that were potentially beneficial to biological evolution.” https://lnkd.in/dDSckgW View in LinkedIn

METEORITE THEORY. “For one thing, “around 600 to 700 million years ago, Earth loses its craters,” notes study coauthor Bill Bottke, a planetary scientist and asteroid expert at the Southwest Research Institute in Boulder, Colorado. Some ancient craters still exist on stable continental cores named cratons, but they are few and far between. (Recently, a city-size impact crater was found under the ice in Greenland.).” https://lnkd.in/ds7GcBF View in LinkedIn