地球生命可能来自外太空

A group of international scientists including a Lawrence Livermore National Laboratory researcher have confirmed that life really could have come from out of this world. The team shock compressed an icy mixture, similar to what is found in comets, which then created a number of amino acids（氨基酸） -- the building blocks of life. The research appears in advanced online publication Sept. 15 on the Nature Geoscience journal website.   This is the first experimental confirmation¹ of what LLNL scientist Nir Goldman first predicted in 2010 and again in 2013 using computer simulations performed on LLNL's supercomputers, including Rzcereal and Aztec.   Goldman's initial research found that the impact of icy comets crashing into Earth billions of years ago could have produced a variety of prebiotic（生命起源以前的） or life-building compounds, including amino acids. Amino acids are critical to life and serve as the building blocks of proteins. His work predicted that the simple molecules² found in comets (such as water, ammonia, methanol甲醇 and carbon dioxide) could have supplied the raw materials, and the impact with early Earth would have yielded an abundant supply of energy to drive this prebiotic chemistry.   In the new work, collaborators from Imperial College in London and University of Kent conducted a series of experiments very similar to Goldman's previous simulations in which a projectile³ was fired using a light gas gun into a typical cometary ice mixture. The result: Several different types of amino acids formed.   "These results confirm our earlier predictions of impact synthesis of prebiotic material, where the impact itself can yield life-building compounds," Goldman said. "Our work provides a realistic additional synthetic⁴ production pathway for the components⁵ of proteins in our solar system, expanding the inventory⁶ of locations where life could potentially originate."   Comets are known to harbor simple ices and the organic precursors⁷ of amino acids. Glycine -- the simplest amino acid -- was recently confirmed to be present in comet Wild-2.   Goldman's original work used molecular⁸ dynamics⁹ simulations to show that shock waves due to planetary impact passing into representative comet mixtures could theoretically drive amino acid synthesis. This synthetic mechanism¹⁰ could yield a wide variety of prebiotic molecules at realistic impact conditions, independent of the external features or pre-existing chemical environment on a planet.   "These results present a significant step forward in our understanding of the origin of the building blocks of life," Goldman said.   The team found that icy bodies with the same compounds created from comet impacts also may be found in the outer solar system. For example, Enceladus (one of Saturn's moons) contains a mix of light organics and water ice. The team concluded that it is highly probable that the impact of a comet traveling with a high enough velocity#p#分页标题#e#¹¹ would impart enough energy to promote shock synthesis of more complex organic compounds, including amino acids, from these ices.   "This increases the chances of life originating and being widespread throughout our solar system," Goldman said.