"Early Life On Earth Possibly 4.4 Billion Years Old"

To study this period, Abramov and colleague Stephen Mojzsis used data from moon rocks, meteorite samples and the dented surfaces of neighboring planets to develop a three-dimensional model of this period of bombardment. "What we did was recreate the Late Heavy Bombardment on a computer," Abramov said, adding that the simulation randomly "smacked the Earth" with giant asteroids. The team then looked at the impact that would have had on the Earth's temperature in the so-called geophysical habitable zone - a zone representing the top 2.5 miles of the Earth's crust.
Based on these models, Abramov said this sustained period of impacts would have killed any life on the Earth's surface, but not all life on Earth, as many had assumed. "We find it is essentially impossible to sterilize the entire habitable zone of the Earth by this kind of bombardment," Abramov said in a telephone interview. "Certainly, the surface of the Earth was sterilized repeatedly," he said. But he said hydrothermal vents below the surface of the Earth may have offered sanctuaries for certain heat-loving microbes, and may have even provided a kind of incubator for life. He said many scientists had thought that a cataclysmic bombardment event would have sterilized the planet and life would have had to start anew. "The important thing about these results is they push back the possible beginnings of life as we know it," he said.
"Exactly when life originated on Earth is a hotly debated topic," said Michael New, an astrobiologist at the National Aeronautics and Space Administration, which sponsored the research. "These findings are significant because they indicated life could have begun well before the Late Heavy Bombardment, during the so-called Hadean Eon of Earth's history 3.8 billion to 4.5 billion years ago," New said in a statement."
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