Martian and terrestrial paleoclimatology: Relevance of solar variability     

William K. Hartmann 《Icarus》1974,22(3):301-311

Evidence for past Martian rivers is perhaps the most puzzling and inconsistent present planetary problem, conflicting as it does with current conditions on the planet. This paper emphasizes the similar puzzling evidence that the Earth, as well as Mars, was warmer in the past. Neutrino evidence raises the suggestion that the sun was also “warmer” in the past. A hypothetical cause reconciling all effects is episodic change in solar luminosity on a time-scale of a few hundred million years. This paper outlines requirements and consequences of such a working hypothesis, with pro and con arguments. It is important to try to prove or disprove this hypothesis because it has radical implications for current science. For example, it suggests (1) climates of all the planets have been markedly altered simultaneously by solar changes, sometimes catastrophically; (2) solar changes have been a dominant “forcing function” driving biological speculation and evolution on Earth; (3) the concept of geologic uniformitarianism is somewhat modified by cosmic variables; (4) evolution of water-utilizing intelligent creatures near other stars may be less likely than has been thought, due to catastrophic planetary climate reactions to change in stellar luminosity.  相似文献   

Origins of life,planetary astronomy: Edited by Lynn Margulis. Springer-Verlag,New York, 1973. 268 pp. Price $14.80     

William K. Hartmann 《Icarus》1973,20(3):406

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Martian cratering 12. Utilizing primary crater clusters to study crater populations and meteoroid properties          下载免费PDF全文

William K. Hartmann  Ingrid J. Daubar  Olga Popova  Emily C. S. Joseph 《Meteoritics & planetary science》2018,53(4):672-686

Images from Mars Global Surveyor and later images from Mars Reconnaissance Orbiter reveal that roughly half of the meteoroids striking Mars (at meter to few decameter crater diameters) fragment in the Martian atmosphere, producing small clusters of primary impact craters. Statistics of these “primary clusters” yield valuable information about important Martian phenomena and properties of interplanetary bodies, including meteoroid behavior in the Martian atmosphere, bulk strengths of bodies striking Mars, and the fraction of Martian “field secondary” craters, a datum that would improve crater count chronometry. Many Martian impactors fragment at altitudes significantly higher than 18 km above the mean surface of Mars, and we find that most bodies striking Mars and Earth have low bulk strengths, consistent with crumbly or highly fractured objects. Applying statistics of primary clusters at various elevations and independent diameter bins, we describe a technique to estimate the percentage of semirandomly scattered “field secondary” craters. Our provisional estimate of this percentage, in the diameter range ~250 m down to ~22 m, is ~40% to ~80% of the total impacts, with the higher percentages at smaller diameters. Our data argue against earlier suggestions of overwhelming dominance by either primaries or secondaries in this diameter range.  相似文献   

Moving beyond the catchment scale: Value and opportunities in large-scale hydrology to understand our changing world     

Daniel G. Kingston  Nicolas Massei  Bastien Dieppois  David M. Hannah  Andreas Hartmann  David A. Lavers  Jean-Philippe Vidal 《水文研究》2020,34(10):2292-2298

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Synthetic near Σ5 (210)/[100] grain boundary in YAG fabricated by direct bonding: structure and stability     

Katharina Hartmann  Richard Wirth  Wilhelm Heinrich 《Physics and Chemistry of Minerals》2010,37(5):291-300

Several macroscopic physical and chemical properties, such as rheology, elasticity, or transport properties are governed by grain boundary processes. An improved understanding of the structure and evolution of grain boundaries has thus become a key challenge in geosciences and material sciences. Here, we report the structure of near Σ5 (210)/[100] grain boundaries in Y₃Al₅O₁₂ (YAG), which were synthesised by the wafer direct bonding method. The produced grain boundaries were annealed at different temperatures, ranging from 673 to 1,873 K. The grain boundaries annealed at different temperatures are not distinguishable based on their flatness and apparent cohesiveness in high resolution TEM (HRTEM) micrographs, but show a considerable step in their mechanical stability at around 1,273 K, a temperature that corresponds to roughly half the melting temperature of YAG. This study further focuses on the effect of a slight misorientation of the two crystals on the grain boundary structure and we discuss if the boundary can reach a state of minimum energy configuration during annealing. Along the grain boundaries, we observed a long-range strain contrast with a periodicity of 40 nm, which has not been reported for high-angle grain boundaries so far. We conclude that this contrast is caused by faceting along the grain boundary plane, which is needed to achieve minimum energy configuration of the grain boundary plane.  相似文献   

Predicting riverine dissolved silica fluxes to coastal zones from a hyperactive region and analysis of their first-order controls   总被引：2，自引：1，他引：1  

Jens Hartmann  Nils Jansen  Hans H. Dürr  Akira Harashima  Kenji Okubo  Stephan Kempe 《International Journal of Earth Sciences》2010,99(1):207-230

Silicate weathering and resulting transport of dissolved matter influence the global carbon cycle in two ways. First by the uptake of atmospheric/soil CO₂ and second by providing the oceanic ecosystems via the fluvial systems with the nutrient dissolved silica (DSi). Previous work suggests that regions dominated by volcanics are hyperactive or even “hot spots” concerning DSi-mobilization. Here, we present a new approach for predicting DSi-fluxes to coastal zones, emphasizing “first-order” controlling factors (lithology, runoff, relief, land cover and temperature). This approach is applied to the Japanese Archipelago, a region characterized by a high percentage of volcanics (29.1% of surface area). The presented DSi-flux model is based on data of 516 catchments, covering approximately 56.7% of the area of the Japanese Archipelago. The spatial distribution of lithology—one of the most important first order controls—is taken from a new high resolution map of Japan. Results show that the Japanese Archipelago is a hyperactive region with a DSi-yield 6.6 times higher than the world average of 3.3 t SiO₂ km⁻² a⁻¹, but with large regional variations. Approximately 10% of its area exceeds 10 times the world average DSi-yield. Slope constitutes another important controlling factor on DSi-fluxes besides lithology and runoff, and can exceed the influence of runoff on DSi-yields. Even though the monitored area on the Japanese Archipelago stretches from about 31° to 46°N, temperature is not identified as a significant first-order model variable. This may be due to the fact that slope, runoff and lithology are correlated with temperature due to regional settings of the Archipelago, and temperature information is substituted to a certain extent by these factors. Land cover data also do not improve the prediction model. This may partly be attributed to misinterpreted land cover information from satellite images. Implications of results for Earth System and global carbon cycle modeling are discussed.  相似文献   

Untersuchung von suspendiertem Material in den Hydrothermallaugen des Atlantis-II-Tiefs     

Dr. Martin Hartmann 《International Journal of Earth Sciences》1973,62(3):742-754

Suspended matter was separated from the hydrothermal brines of the Atlantis-II Deep in the Red Sea. Contents of iron, manganese, copper, and zink collected on membrane filters were measured by X-ray-flourescence, and the main results were:

1. Metal concentrations in suspended form were lower by 10^?1 to 10^?5 compared to the dissolved concentrations of the brines.
2. Suspended copper and zink were enriched most pronounced in the deeper brine zone — markedly so in the SW-basin, values there ranged between 10 and 30μg/l, one Zn-value was as high as 60μ/l, the other basins contained mostly less than 1 to 10μg/l.
3. Iron, copper, and zink in the deeper brine zone and in few cases also in the 50°-brine were suspended in the form of sulfide compounds. This conclusion is based only on the slightly purple-, green-, and blue-colored gray hues of the material on the filters and its rapid oxidation upon contact with the air.
4. In the transition zone of the 50°/60°-brine iron hydroxides were highly concentrated with values ranging up to 1000μg Fe/l.
5. Suspended manganese is found only within the transition zone of brine to the normal sea water, where up to 200μg Mn/l in form of darkbrown manganese hydroxides were found.
6. Concurrently with the increased thermal activity since 1966 more strongly reducing conditions within the brines seemed apparent which were caused by discharge of higher amounts of Sulfides into the basins. Increased precipitation of heavy metal sulfides was found to be most pronounced in the SW-basin.

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Martian hillside gullies and icelandic analogs     

William K Hartmann  Thorsteinn Thorsteinsson 《Icarus》2003,162(2):259-277

We report observations of Icelandic hillside gully systems that are near duplicates of gullies observed on high-latitude martian hillsides. The best Icelandic analogs involve basaltic talus slopes at the angle of repose, with gully formation by debris flows initiated by ground water saturation, and/or by drainage of water from upslope cliffs. We report not only the existence of Mars analog gullies, but also an erosional sequence of morphologic forms, found both on Mars and in Iceland. The observations support hypotheses calling for creation of martian gullies by aqueous processes. Issues remain whether the water in each case comes only from surficial sources, such as melting of ground ice or snow, or from underground sources such as aquifers that gain surface access in hillsides. Iceland has many examples of the former, but the latter mechanism is not ruled out. Our observations are consistent with the martian debris flow mechanism of F. Costard et al. (2001c, Science295, 110-113), except that classic debris flows begin at midslope more frequently than on Mars. From morphologic observations, we suggest that some martian hillside gully systems not only involve significant evolution by extended erosive activity, but gully formation may occur in episodes, and the time interval since the last episode is considerably less than the time interval needed to erase the gully through normal martian obliteration processes.  相似文献   

Electron microprobe dating of monazite substantiates ages of major geological events in the southern Brazilian shield   总被引：1，自引：0，他引：1  

Hugo Tickyj  Lo A. Hartmann  Marcos A. Z. Vasconcellos  Ruy P. Philipp  Marcus V. D. Remus 《Journal of South American Earth Sciences》2004,16(8):84

To obtain the chemical Th^*–Pb isochron ages and surface maps of monazite crystals in igneous and metamorphic rocks from the southern Brazilian Shield, we employ Th–U-total Pb dating by an electron probe microanalyzer. The ages of two Trans-Amazonian metamorphic events are given by a felsic, garnet-bearing granulite from the Santa Maria Chico granulitic complex. The age of the first event, at approximately 2.35 Ga, was obtained by surface mapping in a grain included in garnet. The dating of the second event, 1899±43 Ma, is in agreement with previous data obtained in zircon crystals with sensitive high-resolution ion microprobe. Other determinations belong to the Brasiliano cycle. In the São Gabriel block, an age of 643±129 Ma was obtained on monazite from a staurolite-garnet schist of the Cambaizinho Formation, whereas a staurolite-bearing schist from the Passo Feio complex yielded a 510±68 Ma age. Several units in the Dom Feliciano belt were dated, including the biotite-sillimanite gneisses of the Várzea do Capivarita complex (552±90 Ma), the sillimanite-garnet gneisses of Camboriú complex (565±77 Ma), the Três Figueiras granite (558±57 Ma), and the Plaza Itapema granite (545±55 Ma). The ages presented in this study, obtained through monazite chemical dating, are confirmed through comparison with previous data regarding zircon crystals from the same geological units.  相似文献   

Sm–Nd isotopic investigation of Neoproterozoic and Cretaceous igneous rocks from southern Brazil: A study of magmatic processes     

Maria do Carmo P. Gastal  Jean Michel Lafon  Lo Afraneo Hartmann  Edinei Koester 《Lithos》2005,82(3-4):345-377

Nd-evolutionary paths for diversified igneous suites from southern Brazil are here re-evaluated using published results. We interpret the ε_Nd paths considering the secondary fractionation of ¹⁴⁷Sm/¹⁴⁴Nd due to major petrogenetic processes. The inclusion of Nd isotopes and geochemical data for Precambrian and Mesozoic basic rocks allow improving the discussion on the subcontinental lithosphere beneath southern Brazil. Late Neoproterozoic rocks, mostly granitoids, are exposed in two regions of the southern Brazilian shield, an eastern collisional belt and a western foreland. The latter included two geotectonic domains amalgamated at this time, the São Gabriel Arc (900–700 Ma), and the Taquarembó cratonic block. Magma genesis mainly involved mixture of crustal and incompatible-element-enriched mantle components, both with a long residence time. Continental segments are the Neoarchaean–Paleoproterozoic lower crust (ca. 2.55 Ga) in the western foreland, and Paleoproterozoic–Neoproterozoic recycled crust (2.1–0.8 Ga) in the collisional belt. Granitoids with a single crustal derivation are limited in the southern Brazilian Shield. Mixing processes are well-registered in the western foreland, where the re-enriched old mantle was probably mixed with a 900–700 Ma-old subducted lithosphere and a 2.55 Ga-old lower crust. The contribution of the latter increased from the early 605–580 Ma to the later 575–550 Ma Neoproterozoic events, which may be due either to crustal thickening or to delamination of the lithosphere. Magma sources were diversified in the 660–630 Ma collisional belt. Initially, they involved the mixing between two components with similar Nd isotopic ratios, a 2.1–0.8 Ga-old recycled crust and a subduction-processed old mantle. Regional heating and abundant production of granitic melts, with diversified contribution of enriched mantle components, mark the end of the collisional period, at 630–580 Ma. We can also attribute this to the delamination of the lithosphere, so that the same geodynamic process may explain the magmatism in the whole shield at the end of the Dom Feliciano Orogeny. Mesozoic rocks include flood basalts from the Cretaceous Paraná Province and sub-coeval alkalic suites. Multiple processes of metasomatism affected the lithospheric mantle, resulting in some complexity but they mainly register two enriched-mantle components, both generated during Neoarchaean–Paleoproterozoic events. One end-member has a more pronounced subduction signature. The other one probably resulted from the re-enrichment of the first component at the end of the Camboriú collisional orogeny (2.0 Ga).  相似文献