A Neoproterozoic Snowball Earth

Science

were all forced to smooth inclinometry data because of high levels of noise. 7. The instrument was constructed by Slope Indicator Canada, Ltd. (Vancouver, BC). Measurement errors associated with a prototype of this instrument are discussed by E. W. Blake and G. K. C. Clarke [ J. Glaciol. 38, 113 (1992)]. However, analysis of actual data from the instrument used suggests that instrument errors are slightly improved from manufacturer specifications [ J. T. Harper, thesis, University of Wyoming (1997); S. V. Huzurbazar, unpublished material]. Additionally, the uniformity of the borehole walls enabled a high degree of repeatability for the measurements. 8. We follow the method of C. F Raymond, J. Glaciol. 10, 39 (1971). 9. We use a cubic spline function with an iterative scheme designed to minimize the curvature of the function between data points [I. C. Briggs, Geophysics 1974, 39 (1974)]. This interpolation was tested extensively with synthetic data.

The time period between 2500 M.y to 500 M.y is known as Proterozoic era. During this period the earth underwent many environmental changes. These environmental changes were linked to tectonic activity and silicate weathering. The super continental cycle caused opening of Purana basin I, II and III. These geological processes lead to the development of nascent life forms. Due to the low oxygen level and N-stress condition cyanobacterias existed in deep ocean whereas eukaryotic life existed in the marginal marine environment. The oxygen level crossed minimum threshold value at 570 Ma, causing explosion of life. The tectonism, silicate weathering and high obliquity of earth caused at least five intense glaciations during Proterozoic. During glacial periods land masses as well as marginal marine environment were ice free whereas open oceans were covered with ice. The carbon isotope studies indicate that there were holes in the global ocean ice cover. The Neoproterozoic ocean was animated. The BIF reappeared during Neoproterozoic glaciations. It suggests that deep sulphidic ocean was not a wide spread phenomenon. The erosion of mafic Archean crust was the reason behind the BIF deposition during Proterozoic.

Science, 2005

Proceedings of the …, 2011

The glaciations of the Neoproterozoic Era (1,000 to 542 MyBP) were preceded by dramatically light C isotopic excursions preserved in preglacial deposits. Standard explanations of these excursions involve remineralization of isotopically light organic matter and imply strong enhancement of atmospheric CO 2 greenhouse gas concentration, apparently inconsistent with the glaciations that followed. We examine a scenario in which the isotopic signal, as well as the global glaciation, result from enhanced export of organic matter from the upper ocean into anoxic subsurface waters and sediments. The organic matter undergoes anoxic remineralization at depth via either sulfate-or iron-reducing bacteria. In both cases, this can lead to changes in carbonate alkalinity and dissolved inorganic pool that efficiently lower the atmospheric CO 2 concentration, possibly plunging Earth into an ice age. This scenario predicts enhanced deposition of calcium carbonate, the formation of siderite, and an increase in ocean pH, all of which are consistent with recent observations. Late Neoproterozoic diversification of marine eukaryotes may have facilitated the episodic enhancement of export of organic matter from the upper ocean, by causing a greater proportion of organic matter to be partitioned as particulate aggregates that can sink more efficiently, via increased cell size, biomineralization or increased C∶N of eukaryotic phytoplankton. The scenario explains isotopic excursions that are correlated or uncorrelated with snowball initiation, and suggests that increasing atmospheric oxygen concentrations and a progressive oxygenation of the subsurface ocean helped to prevent snowball glaciation on the Phanerozoic Earth. carbon isotopes | CO2

Paleoceanography, 2003

1] Low-latitude sea level glacial deposits suggest the existence of ''snowball Earth'' conditions in the Neoproterozoic. Previous modeling studies have offered conflicting support for the snowball hypothesis. We use a climate model of intermediate complexity, including an ocean GCM and a sophisticated thermodynamic/ dynamic sea ice component, to conduct a suite of experiments with different orbital/paleogeographical configurations, wind-forcing, and atmospheric CO 2 levels. We show that depending on the orbital configuration and paleogeography, snowball conditions prevail even with atmospheric CO 2 levels up to 1800 ppmv. Overall, our modeling paradigm is consistent with the original snowball hypothesis in which an ice covered ocean surrounds a largely snow and ice-free barren land, with some coastal regions permitting the growth of thick glaciers.

Geophysical Research Letters, 2002

1] The distribution of continents during the Neoproterozoic has been hypothesized to play an important role in the initiation of an ice-covered Earth. In this study, the influence of paleogeography on the Neoproterozoic climate is evaluated using a fully coupled ocean-atmosphere general circulation model (FOAM). Three simulations were completed with different continental distributions. Each simulation included a reduced solar luminosity (93% of present-day) and low atmospheric CO 2 (140 ppmv). Model results indicate that a low-latitude concentration of continents leads to lower tropical temperatures, through reduced receipt of shortwave radiation and a smaller tropical greenhouse effect, but does not significantly affect high-latitude temperatures or sea-ice extent. In contrast, the presence of snow-covered, mid-and highlatitude continents increases the sensible heat transport over the ocean, giving rise to sea-surface cooling, deep-water formation, and an advanced sea-ice margin. Nonetheless, an ice-covered Earth is not simulated in these experiments.

Geobiology, 2022

The Neoproterozoic 'snowball Earth' hypothesis suggests that a runaway ice-albedo feedback led to two intense glaciations around 717-635 million years ago, and this global ice cover would have drastically impacted biogeochemical cycles. Testing the predictions of this hypothesis against the rock record is key to understanding Earth's

Intense glaciation during the end of Cryogenian time (∼635 million years ago) marks the coldest climate state in Earth history – a time when glacial deposits accumulated at low, tropical paleolatitudes. The leading idea to explain these deposits, the snowball Earth hypothesis, predicts globally frozen surface conditions and subfreezing temperatures, with global climate models placing surface temperatures in the tropics between −20 • C and −60 • C. However, precise paleosurface temperatures based upon geologic constraints have remained elusive and the global severity of the glaciation undetermined. Here we make new geologic observations of tropical periglacial, aeolian and fluvial sedimentary structures formed during the end-Cryogenian, Marinoan glaciation in South Australia; these observations allow us to constrain ancient surface temperatures. We find periglacial sand wedges and associated deformation suggest that ground temperatures were sufficiently warm to allow for ductile deformation of a sandy regolith. The wide range of deformation structures likely indicate the presence of a paleoactive layer that penetrated 2–4 m below the ground surface. These observations, paired with a model of ground temperature forced by solar insolation, constrain the local mean annual surface temperature to within a few degrees of freezing. This temperature constraint matches well with our observations of fluvial deposits, which require temperatures sufficiently warm for surface runoff. Although this estimate coincides with one of the coldest near sea-level tropical temperatures in Earth history, if these structures represent peak Marinaon glacial conditions, they do not support the persistent deep freeze of the snowball Earth hypothesis. Rather, surface temperatures near 0 • C allow for regions of seasonal surface melting, atmosphere–ocean coupling and possible tropical refugia for early metazoans. If instead these structures formed during glacial onset or deglaciation, then they have implications for the timescale and character for the transition into or out of a snowball state.

2013

This research is focused on strata deposited in northern Utah during the Cryogenian Period (850 – 635 Ma) of the Neoproterozoic Era, a period that derives its name from the widespread evidence for multiple, likely global, glacial events during this time, commonly referred to as "Snowball Earth" glaciations. This dissertation includes detailed studies of two Cryogenian successions in northern Utah that bracket potential "Snowball Earth" events: the upper part of the Uinta Mountain Group (deposited prior to the glaciations) and the dolomite member of the Kelly Canyon formation (hypothesized to have formed in the aftermath of a global glaciation that terminated at either 665 or 635 Ma). Both successions contain a lithostratigraphic, geochemical, and biotic record of the Earth's oceans before and after the largest-magnitude glaciations in the history of our planet. The pre-glacial upper part of the Uinta Mountain Group in the area mapped for this study contains e...