美国科学家最近提出，约４亿年前地球曾频繁遭受陨石撞击，这可能对地球生命的演化起到了重要推动作用。这项成果发表在３月１０日出版的美国《科学》杂志上。研究认为，约３５亿年前，陨石撞击地球的频率开始平稳下降，但在４亿年前，这一数字突然转跌为升，回复到３５亿年前? U.S. scientists recently suggested that the Earth had suffered frequent meteorite impacts about 400 million years ago, which may have played an important role in promoting the evolution of life on Earth. The result was published in the March 10 issue of Science in the United States. According to the research, the frequency of meteorite impact on the earth began to decline steadily about 3.5 billion years ago. But suddenly, the figure turned to rise 400 million years ago, and returned to 3.5 billion years ago?