Role of major terrestrial cratering events in dispersing life in the solar system (original) (raw)
Related papers
Planetary and Space Science, 2009
It is often assumed that the terrestrial worlds have experienced identical impact regimes over the course of their formation and evolution, and, as a result, would have started life with identical volatile budgets. In this work, through illustrative dynamical simulations of the impact flux on Venus, the Earth, and Mars, we show that these planets can actually experience greatly different rates of impact from objects injected from different reservoirs. For example, we show scenarios in which Mars experiences far more asteroidal impacts, per cometary impactor, than Venus, with the Earth being intermediate in value between the two. This difference is significant, and is apparent in simulations of both quiescent and highly stirred asteroid belts (such as could be produced by a mutual mean-motion resonance crossing between Jupiter and Saturn, as proposed in the Nice model of the Late Heavy Bombardment). We consider the effects such differences would have on the initial volatilisation of the terrestrial planets in a variety of scenarios of both endogenous and exogenous hydration, with particular focus on the key question of the initial level of deuteration in each planet's water budget. We conclude that each of the terrestrial worlds will have experienced a significantly different distribution of impactors from various reservoirs, and that the assumption that each planet has the same initial volatile budget is, at the very least, a gross over-simplification.
The inner solar system cratering record and the evolution of impactor populations
We review previously published and newly obtained crater size-frequency distributions in the inner solar system. These data indicate that the Moon and the terrestrial planets have been bombarded by two populations of objects. Population 1, dominating at early times, had nearly the same size distribution as the present-day asteroid belt, and produced heavily cratered surfaces with a complex, multi-sloped crater size-frequency distribution. Population 2, dominating since about 3.8–3.7 Gyr, had the same size distribution as near-Earth objects (NEOs) and a much lower impact flux, and produced a crater size distribution characterized by a differential –3 single-slope power law in the crater diameter range 0.02 km to 100 km. Taken together with the results from a large body of work on age-dating of lunar and meteorite samples and theoretical work in solar system dynamics, a plausible interpretation of these data is as follows. The NEO population is the source of Population 2 and it has been in near-steady state over the past ∼ 3.7–3.8 Gyr; these objects are derived from the main asteroid belt by size-dependent non-gravitational effects that favor the ejection of smaller asteroids. However, Population 1 was composed of main belt asteroids ejected from their source region in a size-independent manner, possibly by means of gravitational resonance sweeping during orbit migration of giant planets; this caused the so-called Late Heavy Bombardment (LHB). The LHB began some time before ∼3.9 Gyr, peaked and declined rapidly over the next ∼ 100 to 300 Myr, and possibly more slowly from about 3.8–3.7 Gyr to ∼2 Gyr. A third crater population (Population S) consisted of secondary impact craters that can dominate the cratering record at small diameters.
Comets, carbonaceous meteorites, and the origin of the biosphere
Biogeosciences discussions, 2006
The Biosphere is considered to represent the Earth's crust, atmosphere, oceans, and ice caps and the living organisms that survive within this habitat. This paper considers the significance of comets and carbonaceous meteorites to the origin and evolution of the Biosphere and presents new Field Emission Scanning Electron Microscope (FE-SEM) images of indigenous microfossils in the Orgueil and Murchison meteorites. The discovery of microbial extremophiles in deep crustal rocks, hydrothermal vents and ancient ice has established that the biosphere is far more extensive than previously recognized. Chemical and molecular biomarkers and microfossils in Archaean rocks indicate that life appeared very early on the primitive Earth and the origin of the biosphere is closely linked with the emergence of life. The role of comets, carbonaceous meteorites, interstellar dust and asteroids in the delivery of water, organics and prebiotic chemicals to Earth during the Hadean (4.5-3.8 Ga) period of heavy bombardment has become more widely recognized. Spacecraft observations of the chemical compositions and characteristics of the nuclei of several comets (Halley, Borrelly, Wild 2, and Tempel 1) have established that comets contain complex organic chemicals; that water is the predominant volatile; and that high temperatures (∼400 K) can be reached on the black (albedo∼0.03) nuclei when near perihelion. The microscopic dust particles in the Tempel 1 ejecta are similar in size to the particulates of the Orgueil meteorite and evidence is mounting that comets may represent the parent bodies of the CI meteorites. Impact craters and pinnacles on comet Wild 2 suggest a thick crust. Episodic outbursts and jets of Halley, Borrelly, Wild 2 and Tempel 1 near perihelion indicate that localized regimes of liquid water may periodically exist beneath the thick crust of many comets. This increases the possibility that microbial life might survive in comets and therefore the widely accepted view that comets are devoid of liquid water and therefore sterile may be invalid. Consequently, the potential role of comets in the possible delivery of viable microorganisms, as well as water and organic chemicals, to Earth merits further consideration. FESEM investigations of CI and CM carbonaceous mete-24
Reseeding of early earth by impacts of returning ejecta during the late heavy bombardment
Icarus, 2003
Mounting attention has focused on interplanetary transfer of microorganisms (panspermia), particularly in reference to exchange between Mars and Earth. In most cases, however, such exchange requires millions of years, over which time the transported microorganisms must remain viable. During a large impact on Earth, however, previous work (J.C. Armstrong et al., 2002, Icarus 160, 183-196) has shown that substantial amounts of material return to the planet of origin over a much shorter period of time (Ͻ 5000 years), considerably mitigating the challenges to the survival of a living organism. Conservatively evaluating experiments performed [by others] on Bacillus subtilis and Deinococcus radiodurans to constrain biological survival under impact conditions, we estimate that if the Earth were hit by a sterilizing impactor ϳ 300 km in diameter, with a relative velocity of 30 km s Ϫ1 (such as may have occurred during the Late Heavy Bombardment), an initial cell population in the ejecta of order 10 3-10 5 cells kg Ϫ1 would in most cases be sufficient for a single modern organism to survive and return to an again-clement planet 3000-5000 years later. Although little can be said about the characteristics or distribution of ancient life, our calculations suggest that impact reseeding is a possible means by which life, if present, could have survived the Late Heavy Bombardment.
From meteorites to evolution and habitability of planets
Planetary and Space Science, 2012
The evolution of planets is driven by the composition, structure, and thermal state of their internal core, mantle, lithosphere, and crust, and by interactions with a possible ocean and/or atmosphere. A planet's history is a long chronology of events with possibly a sequence of apocalyptic events in which asteroids, comets and their meteorite offspring play an important role. Large meteorite impacts on the young Earth could have contributed to the conditions for life to appear, and similarly large meteorite impacts could also create the conditions to erase life or drastically decrease biodiversity on the surface of the planet. Meteorites also contain valuable information to understand the evolution of a planet through their gas inclusion, their composition, and their cosmogenic isotopes. This paper addresses the evolution of the terrestrial bodies of our Solar System, in particular through all phenomena related to meteorites and what we can learn from them. This includes our present understanding of planet formation, their interior, their atmosphere, and the effects and relations of meteorites with respect to these reservoirs. It brings further insight into the origin and sustainability of life on planets, including Earth. Particular attention is devoted to Earth and Mars, as well as to planets and satellites possessing an atmosphere (Earth, Mars, Venus, and Titan) or a subsurface ocean (e.g., Europa), because those are the best candidates for hosting life. Though the conditions on the planets Earth, Mars, and Venus were probably similar soon after their formation, their histories have diverged about 4 billion years ago. The search for traces of life on early Earth serves as a case study to refine techniques/environments allowing the detection of potential habitats and possible life on other planets. A strong emphasis is placed on impact processes, an obvious shaper of planetary evolution, and on meteorites that document early Solar System evolution and witness the geological processes taking place on other planetary bodies.
Large-scale impact cratering on the terrestrial planets
Advances in Space Research, 1982
Impact cratering as a geologic process on the terrestrial planets is addressed. The crater densities on the Earth and Moon form the basis for a standard flux-time curve, which can be used to date unsampled planetary surfaces and constrain the temporal history of endogenic geologic processes. The attached uncertainties and the shape of the flux curve (a rapid exponential decay for the period 14.6 -'4.0 by, followed by the establishment of a constant flux by 3.5 -3.0 by which continues more or less to the present) are such that only very old C~3 8 by) and very young (~1 0 by) surfaces can be dated with some confidence Dating of intermediate-aged surfaces is more imprecise, a problem which is most significant for the geologic history of Mars.
The Exchange of Impact Ejecta Between Terrestrial Planets
Science, 1996
models that assume stepwse mutaton of the STRP ~m p y that the varlaton of allele sizes Increases Inearly w~th tme (48) [D. 5. Godstein, A. Ruz Lnares, L. L. Cavali-Sforza, M. W. Feldman, Genetics 139, 463 (1995jl. Thus, we can est~mate R as the ratio of varances of allele szes (in base pa~rs) for alleles less than 110 bp (22 5/0.75 = 30.0), glvng a maxlmum age of 167,000 Y.B.P. Because we have considered only a slnge locus, the standard error on this varance-ratlo estmate IS high. However, the apparent lower boundary of 85 bp to the STRP allele slze results In an underestmate of the t~me of orlgn of the Au(-) chromosome in Afrca, so agaln ths estlmate of R is conservatve. 42. Despte a smaller effect~ve populat~on sze of A h -) chromosomes (because of a lower frequency), the mean varlance of STRP alleles on Alu(-j chromsomes among the 10 sub-Saharan Afr~can popua-t~ons is still substantial [64% of the mean varance of STRP alleles on Alu(+) chromosomes], suggest~ng that whle the orig~n of the Alu(-) chromosome IS more recent than the orig~n of the Alu(+j chromosome, it is st11 quite ancent. 43 C B. Str~nger, In The Origin and Evolution ofHumans and Humanness, D. T. Rasmussen Ed. (Jones and Bartett, Boston, 19931, pp. 75-94. 44 M. Slatk~n, Mol Blol. El/ol 12, 473 (1995). 45 Both the STRP and the Alu deletion polymorphism are located In noncodng regions of the CD4 gene and are unlkey to have any functional s~gn~f~cance. Except In the unlikely case of strong posltlve CISactng epstass of functorial varants flankng exons 1 and 2 of the 90-bp Au(-) chromosomes, seecton cannot expla~n the mantenance of the l~nkage d~sequlhbrum seen In non-Afr~can populatons because there would be nothing to prevent format~on of "non-90 bp" Alu(--) chromosomes by recombna-t~on between the markers or mutaton at the STRP, In addtion, the very low frequency of the Alu(-) chromosomes In Asa, the Pacifc islands, and the New World, as well as the very h~gh frequency of 85-bp Alu(+j and 11 0-bp Alu(+) chromosomes In all non-African populat~ons, argues aga~nst strong positive selecton for the Alu(-) chromosome.
Migration of small bodies and dust to the terrestrial planets
Proceedings of the International Astronomical Union, 2004
We integrated the orbital evolution of 30,000 Jupiter-family comets, 1300 resonant asteroids, and 7000 asteroidal, trans-Neptunian, and cometary dust particles. For initial orbital elements of bodies close to those of Comets 2P, 10P, 44P, and 113P, a few objects got Earthcrossing orbits with semi-major axes a<2 AU and moved in such orbits for more than 1 Myr (up to tens or even hundreds of Myrs). Four objects (from 2P and 10P runs) even got inner-Earth orbits (with aphelion distance Q<0.983 AU) and Aten orbits for Myrs. Our results show that the trans-Neptunian belt can provide a significant portion of near-Earth objects, or the number of trans-Neptunian objects migrating inside the solar system can be smaller than it was earlier considered, or most of 1-km former trans-Neptunian objects that had got near-Earth object orbits for millions of years disintegrated into mini-comets and dust during a smaller part of their dynamical lifetimes. The probability of a collision of an asteroidal or cometary particle during its lifetime with the Earth was maximum at diameter d∼100 µm. At d<10 µm such probability for trans-Neptunian particles was less than that for asteroidal particles by less than an order of magnitude, so the fraction of trans-Neptunian particles with such diameter near Earth can be considerable.