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“雪球地球”时代海洋藻类繁荣促使动物诞生

2017-08-17 14:42:05   中国网

新华社北京8月17日电地球上第一批动物是怎样出现的?澳大利亚科学家最近提出,在6亿多年前的“雪球地球”时代,一次升温事件使大量营养物质进入海洋,导致藻类迅速繁荣,为动物的诞生创造了条件。

澳大利亚国立大学研究人员在新一期英国《自然》杂志上报告说,他们从澳大利亚中部地区提取古代沉积岩样本,分析其中的古生物分子,发现在成冰纪晚期短短1000多万年时间里,海洋中的浮游藻类迅速崛起。

成冰纪距今7.2亿年至6.35亿年,是地质史上一个特别寒冷的时期,其中某些阶段地球可能完全被冰雪覆盖,成为“雪球地球”。分子化石证据表明,在成冰纪之前,蓝细菌是海洋唯一的统治者。蓝细菌又称蓝绿藻,是一类能进行光合作用的细菌。

约6.59亿年至6.45亿年前,海洋中的藻类浮游生物猛增,打破了蓝细菌的统治。研究人员说,成冰纪的巨大冰川压碎山脉和岩石,释放出大量营养物质,随后全球气温上升导致冰雪消融,将这些营养物质冲刷进海洋。气温再次降低到合适水平时,海洋环境变得特别适合藻类生长。

丰富的藻类产生了更高效的营养物质和能量转移途径,促使生态系统里进化出更大、更复杂的生物,这是地球生态史上最重要的转变之一。有迹象表明,这期间诞生了原始的海绵动物和有孔虫,在随后的埃迪卡拉纪,出现了种类更为丰富的细胞动物。

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