Como as formas primitivas de vida sobreviveram na Terra Hadeana

quarta-feira, março 11, 2009

Uma nova pesquisa de Oleg Abramov e Steve Moizsis sugere como que as formas primitivas de vidas extremas poderiam ter sobrevivido ao intenso bombardeio de meteoros sobre a Terra.


O. Abramov and S. J. Mojzsis, Department of Geological Sciences, University of Colorado, 2200 Colorado Ave., Boulder, CO 80309.

Introduction: Lunar rocks and impact melts, lunar and asteroidal meteorites, and an ancient martian meteorite record thermal metamorphic events with ages that group around and/or do not exceed 3.9 Ga, which is interpreted to be the result of a cataclysmic spike in the number of impacts commonly referred to as the Late Heavy Bombardment (LHB) [1-3]. This 20-200 Myr [2,4] cataclysm likely resurfaced most of the Earth and may even have vaporized the oceans. Despite its obvious significance to the preservation of crust and the survivability of an emergent biosphere, the thermal effects of this bombardment remain poorly constrained.

Surface habitats for early life would have been doubtlessly destroyed by the intense heat and deposition of global ejecta blankets following basinforming impacts [5]. At the same time, however, new subsurface habitats would have been created in the form of impact-induced hydrothermal systems [6], which provided sanctuary to existing life or may even have been the crucible of its origin. The cessation of the LHB coincides remarkably well with the Proxy stable isotopic evidence for life on Earth by ~3.83 Ga [e.g., 7].

Furthermore, molecular phylogenetic evidence in the form of 16S ssu rRNA phylogenies suggests that all terrestrial life arose from a common ancestral population akin to present-day thermophilic or hyperthermophilic organisms [e.g., 8]. These lines of evidence have been used to suggest that the LHB played an important role in the origin and evolution of life. Conversely, a number of workers have argued that the energy liberated during the bombardment would have precluded the continuous survival of any incipient life [e.g., 9] in one or more “impact frustrations” and disrupted the crust to such a degree that no Earth rocks survive from before about 3.8 Ga [10].

The underlying purpose of this study is to explore the thermal state and habitability of Hadean Earth during the LHB using models that incorporate: (i) new studies of impact cratering records of the Moon and terrestrial planets and size distributions of asteroid populations [e.g., 11]; (ii) data from a new class of early solar system dynamical models that successfully reproduce impact rates during the LHB as defined by the lunar and meteoritic record [e.g., 12]; (iii) more powerful numerical models that assess the thermal response of the lithosphere to impacts of the severity and frequency ascribed to the bombardment.


Lunar and Planetary Science Conference in Texas. PDF gratuito aqui.