我们也许最终会明白，生命是如何在冰雪覆盖的地球上存活下来的

我们也许最终会明白生命是如何在冰雪覆盖的地球上存活下来的

Life has faced many challenges as it has scrambled over this blue marble; many times, it has seemingly reached the brink, only to come back with surprising vigour. Now, researchers have finally figured out how living things could have survived a colossal glaciation event known as the Cryogenian Period.

生命在这块蓝色的大理石上攀爬时，曾面临许多挑战;很多时候，它似乎已经到了悬崖边缘，但却以惊人的活力卷土重来。现在，研究人员终于弄清楚了生物是如何在被称为“低温期”的巨大冰川作用中幸存下来的。

This Snowball Earth, as it is also known, lasted from 720 to 635 million years ago. And you'd think that a layer of ice over the ocean, cutting off the oxygen supply, would have hindered the forward march of animal life; but fossil evidence indicates that this wasn't even remotely the case.

这个被称为雪球的地球，从7.2亿年前持续到6.35亿年前。你可能会认为海洋上的一层冰，切断了氧气供应，会阻碍动物生命的前进;但化石证据表明，情况并非如此。

Rather, life survived, then bloomed in the wake of Snowball Earth. According to the new research, this was possible because meltwater from glaciers created oxygenated pockets in the oceans. In these oases, chemosynthetic life could wait out the ice age to emerge and continue on the other side.

相反，生命存活了下来，然后在雪球地球之后绽放。根据这项新的研究，这是可能的，因为冰川融水在海洋中形成了含氧口袋。在这些绿洲中，化学合成生命可以等待冰河时代的到来，并在另一边继续生存。

"The evidence suggests that although much of the oceans during the deep freeze would have been uninhabitable due to a lack of oxygen, in areas where the grounded ice sheet begins to float there was a critical supply of oxygenated meltwater," explained sedimentologist Maxwell Lechte of McGill University in Canada.

加拿大麦吉尔大学(McGill University)的沉积学专家麦克斯韦尔·莱赫特(Maxwell Lechte)解释说：“证据表明，虽然在深度冰冻期间，由于缺氧，大部分海洋将不适合居住，但在被搁浅的冰盖开始漂浮的地区，含氧融水的供应是至关重要的。”。

"This trend can be explained by what we call a 'glacial oxygen pump'; air bubbles trapped in the glacial ice are released into the water as it melts, enriching it with oxygen."

“这种趋势可以用我们所说的‘冰川氧泵’来解释;冰层中的气泡在融化时被释放到水中，使其富含氧气。”

Although the fossil record from that time is really, really sparse, there are geological traces of the conditions on Earth at the time. The sediments deposited on the seafloor, specifically those rich with iron, allowed Lechte and his team to reconstruct the oxygenation levels.

尽管那个时候的化石记录非常非常少，但是有当时地球上的地质条件的痕迹。沉积在海底的沉积物，特别是那些富含铁的沉积物，使得莱克特和他的团队能够重建氧合水平。

Previously, it had been assumed that life must have somehow held out in meltwater puddles on the surface, but what the team found suggests another way.

以前，人们认为生命一定以某种方式存在于地表的融水水坑中，但研究小组的发现表明了另一种方式。

They studied iron formations across three continents - the Chuos Formation in Namibia, the Yudnamutana Subgroup in Australia, and the Kingston Peak Formation in the US.

他们研究了三大洲的铁建造——纳米比亚的丘斯组、澳大利亚的尤德纳穆塔纳亚组和美国的金斯敦峰建造。

Overall, iron isotope ratios and cerium anomalies from glaciomarine environments reveal that the waters were mostly extremely oxygen-deprived - but the closer one draws to the ice-shelf grounding line, the more oxidised the deposits grow.

总的来说，从冰川环境中的铁同位素比率和铈异常揭示了水大部分是极度缺氧的，但是越靠近冰架接地线，沉积物越氧化。

Any eukaryotic life that lived in those aerated waters would also have needed food in order to thrive. The iron may be a clue to this.

任何生活在这些充气水中的真核生物也需要食物才能茁壮成长。铁可能是一个线索。

We know that the seawater was rich in dissolved iron. And we know that today, there exist chemotrophic bacteria that derive their energy from the oxidation of dissolved iron, shedding the iron oxides when they are done with it.

我们知道海水中含有丰富的溶解铁。我们知道，今天，存在着化学营养细菌，它们从溶解的铁的氧化中获取能量，当它们处理完铁氧化物时，就会脱落。

So the oxidised deposits around the ice shelf grounding line could have been caused by iron-oxidating marine bacteria, drawn to and thriving in the oxygenated water.

因此，冰架接地线周围的氧化沉积物可能是由海洋中氧化铁的细菌引起的，这些细菌被含氧的水吸引并大量繁殖。

We have no hard proof that this occurred, of course, but it's a credible theory that fits the available evidence - and it neatly wraps up a couple of conundrums about Snowball Earth.

当然，我们没有确凿的证据来证明这一点，但这是一个符合现有证据的可信理论——它巧妙地掩盖了关于雪球地球的几个谜团。

"[The study] not only provides an explanation for how early animals may have survived global glaciation, but also eloquently explains the return of iron deposits in the geological record after an absence of over a billion years," said Earth scientist Galen Halverson of McGill University.

“(这项研究)不仅解释了早期动物是如何在全球冰川作用下生存下来的，而且有力地解释了在消失了十亿多年之后，地质记录中铁质沉积的回归，”麦吉尔大学的地球科学家盖伦·哈尔弗森说。

We'll need more research to figure out how these environments could have sustained a food web. There are glacial ecosystems and ecosystems in the frozen polar regions that support a surprising diversity of life today; these could be good places to look next, the researchers suggest.

我们需要更多的研究来弄清楚这些环境是如何维持食物网的。在冰冻的极地地区存在着冰川生态系统和生态系统，它们支撑着今天惊人的生物多样性;研究人员表示，这些地方可能是下一个值得研究的地方。

The research has been published in PNAS.

这项研究发表在《美国国家科学院院刊》上。