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研究发现丨古人类离开非洲的原因——逃离干旱气候

原标题:研究发现丨古人类离开非洲的原因——逃离干旱气候

Ancient Humans Left Africa to Escape Drying Climate, Says Study

一项新的研究表明,古人类迁离非洲是为了逃离干旱的气候。该发现与此前的认识相矛盾:之前人们认为古人类之所以能离开,是由于当时潮湿的气候使他们能够穿越普遍干旱的中东和非洲之角。此研究发表在《地质学》期刊上。

Ancient humans migrated out of Africa to escape a drying climate, says a new study—a finding that contradicts previous suggestions that ancient people were able to leave because a then-wet climate allowed them to cross the generally arid Horn of Africa and Middle East. The study appears in the journal Geology.

新的研究调查了约70,000到55,000年前的区域性气候,人们认为那时的古人类已经迁离了(非洲)大陆。尽管人类或许在更早的时候就离开了非洲,但基因研究表明,人类向欧亚大陆的迁徙与该迁徙最终导致的人类在世界其他地区的定居,很可能发生在这段时间前后。

The new study examines regional climate some 70,000 to 55,000 years ago, when ancient people are thought to have migrated out of the continent. While humans may have left Africa earlier, genetic research indicates that the main migration into Eurasia that eventually peopled the rest of the world probably occurred around then.

“长期以来,人们认为‘走出非洲’得益于湿季创造了通往欧亚大陆的绿色走廊。也就是说,是气候把人们(从非洲)‘拉’了出来。”该研究的共同作者、哥伦比亚大学拉蒙特—多尔蒂地球观测站的气候学家Peter de Menocal说道,“我们可能不得不将这个模型修正为:人们被恶劣的条件‘推’了出来。”德梅诺卡尔长期以来一直在探究气候如何影响早期人类的发展和分散。

"It has long been proposed that the out-of-Africa migration was facilitated by wet periods that created green corridors to Eurasia—in other words, the climate pulled people out," said study coauthor Peter de Menocal, a climatologist at Columbia University's Lamont-Doherty Earth Observatory. "We may have to revise this model to one where people were pushed out, due to unfavorable conditions." De Menocal has long been exploring how climate may have affected early human development and dispersal.

通过分析从离今索马里不远的亚丁湾最西端提取的海洋沉积物岩心,研究人员能够探查到200,000年前非洲之角的气候。该研究的第一作者、来自亚利桑那大学的Jessica Tierney说,针对岩心的研究表明,人类迁徙时气候不仅变得更为干燥,还变得更为寒冷。“我们的数据显示,迁徙发生在一次巨大的环境变化之后。人们或许是因为环境的不断恶化而离开的。”她说。

The researchers were able to trace the climate of the Horn of Africa back 200,000 years by analyzing a core of ocean sediment taken in the western end of the Gulf of Aden, off present-day Somalia. The study's lead author, Jessica Tierney of the University of Arizona, said the core showed that in addition to drying around the time of the human migration, the region also became cooler. "Our data say the migration comes after a big environmental change. Perhaps people left because the environment was deteriorating," she said.

早期人类迁徙的气候证据来自拉蒙特—多尔蒂地球观测站深海岩心库保存的沉积物。

Evidence for the climate during early human migrations came from sediment kept at the deep-sea core repository at Lamont-Doherty Earth Observatory.

Tierney、de Menocal及其同事此前已经通过研究海洋沉积物岩心绘制了非洲之角的气候图。他们希望使用相同的方法重建该地区55,000到70,000年前的气候,但面临的第一个挑战是找到那个年代的沉积物岩心。最终,他们在拉蒙特—多尔蒂岩心库找到了一份合适的岩心,它于1965年被拉蒙特海洋研究船“罗伯特·D·康拉德号”采集。德梅诺卡尔测定了其岩层所属的年代,发现它含有200,000年前的沉积物。

Tierney, de Menocal and colleagues had previously charted the Horn of Africa's climate back 40,000 years by studying cores of marine sediment. They hoped to use the same means to reconstruct the region's climate back 55,000 to 70,000 years ago, but the first challenge was finding a core with sediments that old. They found one at the Lamont-Doherty Core Repository. It had been collected in 1965 by the Lamont research ship Robert D. Conrad. De Menocal dated its layers and found it had sediments going back as far as 200,000 years.

在亚利桑那大学,Tierney和共同作者Paul Zander从沉积岩层内保留的有机质中梳理出了温度和降水记录。他们从岩心中每10厘米(约四英寸)提取一份样品,这个距离代表了约1600年的时间跨度。

At the University of Arizona, Tierney and coauthor Paul Zander teased out temperature and rainfall records from organic matter preserved in the sediment layers. The scientists took samples from the core every 10 centimeters (about four inches), a distance that represented about every 1,600 years.

为了建立长期的温度记录,研究人员分析了沉积岩层中名为“长链烯酮”(alkenone)的化学物质,该物质由某种特定海藻产生。藻类根据水温改变长链烯酮的构成。不同长链烯酮的比例表明了藻类存活时的海表温度,也反映了当时的地区温度。

To construct a long-term temperature record, the researchers analyzed the sediment layers for chemicals called alkenones, made by a particular kind of marine algae. The algae change the composition of the alkenones depending on the water temperature. The ratio of different alkenones indicates the sea surface temperature when the algae were alive and also reflects regional temperatures.

为了发现该地区古代的降水模式,研究人员分析了从陆生植物上吹到海洋里的叶蜡残留。气候的干湿变化会导致植物改变覆于其叶片上叶蜡的化学成分,为我们提供了过去降雨波动的信息。Tierney说,这些分析表明,人类走出非洲的时候,恰好也是气候发生重大变化,变得更加干燥和寒冷的时候。

To figure out the region's ancient rainfall patterns, there searchers analyzed the remains of leaf wax that had blown into the ocean from terrestrial plants. Because plants alter the chemical composition of the wax covering their leaves depending on how dry or wet the climate is, this provides a record of past fluctuations in rainfall. The analyses showed that the time people migrated out of Africa coincided with a big shift to a much drier and colder climate, Tierney said.

该团队的发现得到了其他研究者的证实——他们利用从以色列洞穴形成和东地中海沉积物岩心获取的数据重建了过去的区域气候。这些发现表明当时的非洲东北部到处都很干燥。

The team's findings are corroborated by research from other investigators who have reconstructed past regional climate by using data gathered from a cave formation in Israel and a sediment core from the eastern Mediterranean. Those findings suggest that it was dry everywhere in northeast Africa.

“我们的主要观点很简单,” Tierney说,“我们认为人类离开非洲去向世界其他地方时,气候是非常干燥的。”

"Our main point is kind of simple," Tierney said. "We think it was dry when people left Africa and went on to other parts of the world."

该研究由美国国家科学基金会(National Science Foundation)和大卫与露西尔·帕克德基金会(Davidand Lucile Packard Foundation)提供资金支持。

The U.S. National Science Foundation and the David and Lucile Packard Foundation funded the research.

The translation is for your reference only.

译文仅供参考,内容以英文为准

编译:南心

校对:忆念

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声明:本文由入驻搜狐号的作者撰写,除搜狐官方账号外,观点仅代表作者本人,不代表搜狐立场。
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