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Water and life
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Lightning is a dramatic display of electrical power, but it is also sporadic and unpredictable. Even on a volatile Earth billions of years ago, lightning may have been too infrequent to produce amino acids in quantities sufficient for life a fact that has cast doubt on such theories in the past, Zare said.
Water spray, however, would have been more common than lightning. A more likely scenario is that mist-generated microlightning constantly zapped amino acids into existence from pools and puddles, where the molecules could accumulate and form more complex molecules, eventually leading to the evolution of life.
“Microdischarges between obviously charged water microdroplets make all the organic molecules observed previously in the Miller-Urey experiment,” Zare said. “We propose that this is a new mechanism for the prebiotic synthesis of molecules that constitute the building blocks of life.”
However, even with the new findings about microlightning, questions remain about life’s origins, he added. While some scientists support the notion of electrically charged beginnings for life’s earliest building blocks, an alternative abiogenesis hypothesis proposes that Earth’s first amino acids were cooked up around hydrothermal vents on the seafloor, produced by a combination of seawater, hydrogen-rich fluids and extreme pressure.
Researchers identified salt minerals in the Bennu samples that were deposited as a result of brine evaporation from the asteroid’s parent body. In particular, they found a number of sodium salts, such as the needles of hydrated sodium carbonate highlighted in purple in this false-colored image salts that could easily have been compromised if the samples had been exposed to water in Earth’s atmosphere.
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Yet another hypothesis suggests that organic molecules didn’t originate on Earth at all. Rather, they formed in space and were carried here by comets or fragments of asteroids, a process known as panspermia.
“We still don’t know the answer to this question,” Zare said. “But I think we’re closer to understanding something more about what could have happened.”
Though the details of life’s origins on Earth may never be fully explained, “this study provides another avenue for the formation of molecules crucial to the origin of life,” Williams said. “Water is a ubiquitous aspect of our world, giving rise to the moniker ‘Blue Marble’ to describe the Earth from space. Perhaps the falling of water, the most crucial element that sustains us, also played a greater role in the origin of life on Earth than we previously recognized.”
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- 25/4/16(水) 12:37 -
