Formation of the Post Lunar Earths Atmosphere An Accretion Formula Born with the Moon

The Moon was formed by a giant Mars-sized impact with the Earth, which occurred near the end of the formation time interval of the Earth, A (Earth), as shown by Canup and Asphaug (2001). This impact blew off the pre-lunar atmosphere (cf. Sect. 10, first rubric). It thus left a vacant niche for the Fig. 3.3. Isotopic composition of various types of waters, including the constituent water of the CI and CM hydrous-carbonaceous chondrites (upper histogram), and the constituent water of Antarctic...

Micrometeoritic Sulfur and the Worlds of Iron Sulfides and Thioesters

About 80 of the AMMs collected near the margin of the Antarctic ice sheets did show anomalous low sulfur contents ( 0.1 ) with regard to the value of 3 measured in CM1 chondrites. So, sulfur could have been preferentially lost during either atmospheric entry (as SO2) or cryogenic weathering near the sea shore, involving the preferential leaching of sulfides in the fine-grained matrix of AMMs. The fact that their solar neon is not markedly lost favors this last possibility, because it is mostly...

Implications for the Mass Flux on Early Earth

The uncertainties in the time evolution of the lunar cratering flux, and hence the impactor flux incident on early Earth, emphasize that it is wise in assessments of the role of exogenous sources in the origins of life on the Earth to focus on mass flux at a particular time in Earth history (Chyba and Sagan, 1992 Chyba and Sagan, 1997). This flux need not carry with it the requirement that the full-time evolution of any given model be accepted, and allows a straightforward (multiplicative)...

The Challenge of Comets

Both active short-period comets and extinct comets discovered by the Space-guard Survey are equivalent to asteroids for purposes of the present discussion. However, long-period comets pose an entirely different class of problems. Since these comets do not reside in near-Earth space, no survey can hope to discover them decades before they approach the Earth. They might appear at any time, and discovery cannot be expected more than a few months before the possible impact. Furthermore, since no...

Post Lunar Micrometeoritic Greenhouse Effect

A remarkable balance between the absorption and scattering of solar radiation by the early Earth produced the gentle greenhouse effect that allowed the birth of life. But when was it triggered In the last 20 years, all models have attributed a key role to the paradox of the faint early Sun, where the lower luminosity of the Sun (by up to a factor of 30 ) would have frozen the early oceans. But, this cooling was counterbalanced by the effects of greenhouse gases, such as CO2 and H2O (Owens et...

Prebiotic Organic Syntheses

The origin of the atmosphere and of the oceans that has just been described has direct connections with the origins of life on Earth. In particular, the carbonaceous chondrites that were brought onto the Earth (Table 2.2) from the asteroid belt, mostly during the first 200 million years (Fig. 2.4), contained numerous amino acids. As an example, 74 different amino acids were extracted from the Murchison meteorite, a CM carbonaceous chondrite that fell in 1969 near Murchison, Australia (Cronin et...

Comets and the Origin on Life An Idea with a Long History

There is an old scientific tradition linking cometary phenomena with the appearance of life. Prompted and funded by Edmund Halley, Isaac Newton published in 1686 his Principia, a book that represents a major breakthrough in the development of Western thought. But not even the grave and pompous Sir Isaac, for all his love for mathematical accuracy, was immune to the appeal of popular beliefs, even if they had not been experimentally proven. As summarized by Oparin (1938), more than once Newton...

Terminal Lunar Cataclysm

The model presented in (6.1) and (6.2) assumes a monotonically falling lunar cratering curve-viz., that of Fig. 6.4. But this model for the lunar cratering history is under considerable debate. Recent evidence, in the form of accurate dating for impact melts within the breccia of lunar meteorites, is consistent with the hypothesis that a brief, intense period of bombardment occurred approximately 3.9 Gyr ago, prior to which the Earth-Moon system was in a relatively quiet impact period (Cohen et...

About Ga Impact Clusters and Associated Tsunami

The Jeerinah Impact layer (JIL) (Simonson et al., 2000 Glikson, 2004) consists of a sequence of siltstone, chert and mafic volcanics, capped by a 40-cm-thick microkrystite spherule-bearing rip-up breccia, a lenticular spherule unit up to about 60 cm thick, with an overlying 70-cm-thick boulder-size debris-flow conglomerate. The sequence represents initial current and or seismic disturbance of the seabed, settling of microkrystite spherules, subsequent slumps and debris flow (Fig. 8.5.A-D). The...

Numerical Models for a Protosolar Accretion Disk

We will limit our discussion to the viscous accretion disks because their study has been developed more than that of other possible mechanisms. Following rather general assumptions that we will not review here, in particular on the viscosity behavior of the disk, there remains two parameters, the collapse time and the viscosity coefficient, that can be combined into one. Larson (1984) has established the order of magnitude of the collapse time, by the following considerations. The center of the...

The Conditions for Liquid Water in Cometary Nuclei

Department of Geophysics and Planetary Sciences, Tel Aviv University, Ramat Aviv 69 978, Israel, morris post.tau.ac.il Summary. Liquid water is considered fundamental for the development of life. Comet nuclei are composed largely of ice, and under the proper conditions, some of that ice may transform into liquid water. We describe the physical processes involved in computing the heat balance in comet nuclei and present the results of numerical models of their thermal evolution. We determine...

Micrometeoritic Iridium in the Earths Mantle

Accordingly to a conventional view about the fate of iridium on the early Earth (cf. Rushmer et al., 2000), iridium was initially stored in both the planetesimals that did form the proto-Earth and the planetary embryos (i.e., protoplanets) that subsequently merged to it. Each impact by bodies ranging from 10-km size planetesimals, comets, and asteroids to Mars-sized planetary embryos would lead to the production of pockets of liquid silicates in which droplets of liquid iron nucleate. Metal...

Orbital Diffusion of Comets

Safronov (1972) has shown how the total mass of the perturbed comets is linked to the total mass of the giant planets' embryos. When these embryos became large enough, they were able to eject comets out of the solar system, as well as to store a small fraction of them in a sphere of some 50,000 AU radius. Stellar perturbations removed most of the perihelia of the latter comets from the zones of the planets hence, their orbits became secularly stable and formed the primitive Oort cloud whose...

Interplanetary Dust Particles and Micrometeorites

Anders (1989) has estimated the flux of intact organic matter reaching the Earth's surface in the form of interplanetary dust particles (IDPs). Particles in the mass range 10-15-10-9 kg (or about 0.6-60 m in radius for a typical density of 1 g cm-3) are sufficiently gently decelerated in the upper atmosphere to avoid being heated to temperatures where their organics are pyrolyzed. With a terrestrial mass flux of 3.2 x 106 kg yr-1 of IDPs in this size range, and an average IDP organic mass...

Isotopic Composition of Water

The isotopic composition of the constituent water of individual HCCs and AMMs can be plotted as the distribution of their D H ratios. In Fig. 3.3, we first reported the distributions measured for CI and CM chondrites (top and middle histograms, respectively), which were deduced from data recently reported by Eiler and Kitchen (2003). The bottom histogram refers to the distribution obtained from the ion microprobe analysis of 52 AMMs (Engrand and Maurette, 1998 Engrand et al., 1999). Other...

Impactor Mass Distribution

The mass distributions of asteroids and comets are usefully described by power laws of form where N(> m) is the cumulative number of objects with mass greater than m, q is the exponent of the differential mass distribution dN dm, and C is a constant related to mi, the largest object in the distribution. The differential form is useful for integations. The most important properties of the power law are that it is scale-free and that, for q < 2, most of the mass is in the largest objects. The...

Possible and Demonstrated Connections Between Extraterrestrial Impacts and Habitats of Life

Of the wide range of physical environmental controls over recorded habitats of stromatolite-like, probable stromatolites and confirmed stromatolite colonies Fig. 8.8. Approximately 2.47-2.50-Ga Dales Gorge Iron Member S4 Macroband (DGS4) impact fallout unit. (A) stilpnomelane-dominated tuff and siltstone (SS) overlain by a 20-cm-thick microkrystite spherule unit (MKR), overlain by siderite chert (SC), Fortescue Falls (B) Boulder of banded chert (CB) incorporated in the upper part of DGS4,...

Energy Considerations

If we assume that the comet interior has an initial temperature 20 K, then the energy required to heat a gram of ice to 260 K can be found by integrating the product of the heat capacity (Klinger, 81) and the temperature change from 20 to 260 K. The result is 2.73 x 109 erg g-1. Because of the temperature dependence of the heat capacity, an initial temperature of 50 K would reduce this by only 4 . For the radioactive materials that are relevant to the problem, the total energy available per...

Microfossils and Stromatolites

Strong fossil evidence for ancient microscopic life is present in 3-Gyr-old rocks, less-certain fossil evidence exists in 3.5-Gyr-old rocks, and substantially more controversial isotopic evidence exists in 3.8-Gyr-old rocks. Carbonate deposits in 3-Gyr-old South African sedimentary rocks show well-preserved stromatolites that match well with similar, known biogenic structures seen in much younger rocks and even in modern aqueous sedimentary environments Beukes and Lowe, 1989 . Similar...

Interstellar Dust and the PQQEnigma for Catalysis

Looking more carefully into the chemical structure of primordial coenzymes there is an astonishing diversity in unity Duine, 1999 . A huge diversity of, mostly nucleophilic, reactions very important for peptide as well as for RNA synthesis, already on an early bacterial level, are catalyzed by substances of astonishing unity in chemical structure, namely of quinoic type. For instance, flavines related to flavones are quinoic, riboflavine and a lot of quinoproteins and even quinohemoproteins...

Hydrocode Simulations

We carried out numerical simulations of impact cratering events on various planetary surfaces, using both two-dimensional 2D and three-dimensional 3D hydrocodes. Earlier studies were carried out using the 2D Eulerian hydrocode CSQ , developed at Sandia National Laboratories Thompson, 1979 1985 . By assuming axial symmery, CSQ is used to model vertical impacts. However, it is well known that the most probable impact angle is 45 Gilbert, 1893 Shoemaker, 1962 . Modeling the impact process in its...

References

Alden, W.C. 1929 , Thomas Chrowder Chamberlin's contributions to glacial geology. Jour. Geo., 37, 293-319. Allen, C.S. 1973 , Astrophysical Quantities The Athlone Press, London . Alvarez, W. and Muller, R.A. 1984 , Evidence from crater ages for periodic impacts on Earth. Nature, 308, 718-720. Alvarez, L.W., Alvarez, W., Asaro, F., and Michel, H.V. 1980 , Extraterrestrial cause for the Cretaceous-Tertiary extinction, Science, 208, 1095-1108. Anders, E. 1989 , Pre-biotic organic matter from...

The Integrated Micrometeorite Flux The Lunar Cratering Estimates

We used the smooth, roughly exponential decay, of lunar cratering rates, K t , relatively to the present-day value Fig. 3.4 , given by Hartmann 1999 . This curve gives a monitoring of the dominant population of crater forming bodies with sizes gt 500 m existing in the interplanetary medium at any given time. Fig. 3.4. Variation with time of relative lunar cratering rates, K t . This curve represents the conjuncture of the late heavy bombardment, proposed by Hartmann. Such rates refer to the...

Radioactive Heating

In the years since the work of Whipple and Stefanic 1966 , our picture of radioactive heating has changed in several ways. One of the most important is the realization that 26 Al, an extinct radionuclide, may have been an important heat source. In 1976, Lee et al. presented strong evidence that 26Al had been present in the early solar nebula. Afterwards 7-ray observations from the HEAO 3 and Solar Maximum Mission satellites detected 26Al dispersed throughout the galaxy Mahoney et al., 1982...

Rock Vapor

Panel a of Fig. 7.5 begins at this point. The rock vapor atmosphere radiates to space with an effective temperature of order 000 K. The saturation vapor pressure of rock is sensitive to temperature, and therefore the cloudtop temperature is relatively insensitive to details. The high radiating temperature demands rapid condensation and corresponding very strong updrafts. In addition to the updrafts associated with weather, there is a net updraft of w 0.4 Trad 2000 K 4 p 60 bars cm s below the...

Volcanism Nebular Gases and Comets

The two first processes are generally disregarded to day cf. Owens 1998 and Delsemme 1997 . In particular, Hawaiian volcanoes eject gases generated by the most primitive deep-seated magma originating from the undegassed part of the Earth's mantle. Their H2O N2 and CO2 N2 ratios Table 3.1, column 6 do not fit the corresponding ratios measured for the atmosphere column 4 . About the capture of nebular gases, the Ne N2 ratio predicted for the solar nebula is about 105 times higher than the...