Bringing Exoplanet Habitability Investigations to High School

Habitability, a.k.a. habitat suitability, is a topic typically discussed in Biology class. We present here a curriculum unit that introduces the topic of global-scale planetary habitability in a Physics classroom, allowing students to emulate the process of doing cutting-edge science and re-framing an otherwise "typical" physics unit in a more engaging and interactive way

Neoproterozoic Stratigraphic Comparison of the Lesser Himalaya (India) and Yangtze Block (South China): Paleogeographic Implications

Recent studies of terminal Neoproterozoic rocks (ca. 590–543 Ma) in the Lesser Himalaya of northwestern India and the Yangtze block (south China) reveal remarkably similar facies assemblages and carbonate platform architecture, with distinctive karstic unconformities at comparable stratigraphic levels. These similarities suggest that south China may have been located close to northwestern India during late Neoproterozoic time, an interpretation permitted by the available, yet sparse paleomagnetic data. Additional parallels in older rocks of both blocks—similar rift-related siliciclastic-volcanic successions overlying metamorphic basement, and comparable glaciogenic intervals of possibly Sturtian and Marinoan or Varanger age—suggest that this spatial relationship may have developed earlier in the Neoproterozoic. With the exception of basal Cambrian phosphorite and comparable small shelly fossils, stratigraphic contrasts between northern India and south China and increasing biogeographic affinity between south China and northwestern Australia suggest that south China may have migrated toward northwestern Australia during the Cambrian

Reply

The authors respond to Hoffman et al. (2001), who acknowledged that methane may have played an important role in unusual events associated with Neoproterozoic glaciation, but questioned the authors' permafrost gas hydrate hypothesis for 13C-depleted cap carbonate formation. The critique focused on three issues: (1) an interpretation for tube structures in cap carbonates unrelated to gas migration; (2) the absence of a suitable source for methane gas; and (3) the degree of 13C depletion in sheet-crack cements

Reply

The authors address additional comments on their hypothesis for the origin of Neoproterozoic postglacial cap carbonates and their isotopic excursions

Considering a Neoproterozoic Snowball Earth

P. F. Hoffman et al. and N. Christie-Blick et al. discuss Hoffman et al.'s paper that "developed a modified 'snowball Earth' hypothesis (2) to explain the association of Neoproterozoic low-latitude glaciation with the deposition of 'cap carbonate' rocks bearing highly depleted carbon isotopic values (δ13C ≤ −5‰). According to Hoffman et al., the ocean became completely frozen over as a result of a runaway albedo feedback, and primary biological productivity collapsed for an interval of geological time exceeding the carbon residence time (greater than 105 years). During this interval, continental ice cover is inferred to have been thin and patchy owing to the virtual elimination of the hydrological cycle.

Are Proterozoic Cap Carbonates and Isotopic Excursions a Record of Gas Hydrate Destabilization Following Earth’s Coldest Intervals

Regionally persistent, thin intervals of carbonate rock directly and ubiquitously overlie Proterozoic glacial deposits on almost every continent, and are commonly referred to as cap carbonates. Their unusual facies, stratigraphically abrupt basal and upper contacts, and strongly negative carbon isotopic signature (δ13C values between ∼0‰ and −5‰) suggest a chemical oceanographic origin, the details of which remain unresolved. Here we propose that these enigmatic deposits are related to the destabilization of gas hydrate in terrestrial permafrost following rapid postglacial warming and flooding of widely exposed continental shelves and interior basins. Supporting evidence for this hypothesis includes (1) the common occurrence within the cap carbonates of unusual fabrics, similar to those produced by cold methane seeps; (2) a distinctive time evolution for the carbon isotopic excursions indicative of a pulse addition of isotopically depleted carbon to the ocean- atmosphere system; and (3) agreement between mass-balance estimates of carbon released by hydrate destabilization and carbon buried in the cap carbonate. We infer that during times of low-latitude glaciation, characteristic of the Neoproterozoic, gas hydrates may have been in greater abundance than at any other time in Earth history

Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics 1.0: A General Circulation Model for Simulating the Climates of Rocky Planets

Resolving Orbital and Climate Keys of Earth and Extraterrestrial Environments with Dynamics (ROCKE-3D) is a 3-Dimensional General Circulation Model (GCM) developed at the NASA Goddard Institute for Space Studies for the modeling of atmospheres of Solar System and exoplanetary terrestrial planets. Its parent model, known as ModelE2 (Schmidt et al. 2014), is used to simulate modern and 21st Century Earth and near-term paleo-Earth climates. ROCKE-3D is an ongoing effort to expand the capabilities of ModelE2 to handle a broader range of atmospheric conditions including higher and lower atmospheric pressures, more diverse chemistries and compositions, larger and smaller planet radii and gravity, different rotation rates (slowly rotating to more rapidly rotating than modern Earth, including synchronous rotation), diverse ocean and land distributions and topographies, and potential basic biosphere functions. The first aim of ROCKE-3D is to model planetary atmospheres on terrestrial worlds within the Solar System such as paleo-Earth, modern and paleo-Mars, paleo-Venus, and Saturn's moon Titan. By validating the model for a broad range of temperatures, pressures, and atmospheric constituents we can then expand its capabilities further to those exoplanetary rocky worlds that have been discovered in the past and those to be discovered in the future. We discuss the current and near-future capabilities of ROCKE-3D as a community model for studying planetary and exoplanetary atmospheres.Comment: Revisions since previous draft. Now submitted to Astrophysical Journal Supplement Serie

Paleomagnetic Polarity Reversals in Marinoan (ca. 600 Ma) Glacial Deposits of Australia: Implications for the Duration of Low-Latitude Glaciation in Neoproterozoic Time

A paleomagnetic investigation of Marinoan glacial and preglacial deposits in Australia was conducted to reevaluate Australia's paleogeographic position at the time of glaciation (ca. 610–575 Ma). The paleomagnetic results from the Elatina Formation of the central Flinders Ranges yield the first positive regional-scale fold test (significant at the 99% level), as well as at least three magnetic polarity intervals. Stratigraphic discontinuities typical of glacial successions prevent the application of a magnetic polarity stratigraphy to regional correlation, but the positive fold test and multiple reversals confirm the previous low paleolatitude interpretation of these rocks (mean D = 214.9°, I = −14.7°, α95 = 12.7°, paleolatitude = 7.5°). The underlying preglacial Yaltipena Formation also carries low magnetic inclinations (mean D = 204.0°, I = −16.4°, α95 = 11.0°, paleolatitude = 8.4°), suggesting that Australia was located at low paleolatitude at the onset of glaciation. The number of magnetic polarity intervals present within the Elatina Formation and the Elatina's lithostratigraphic relationship to other Marinoan glacial deposits suggest that glaciation persisted at low latitudes in Australia for a minimum of several hundreds of thousands to millions of years