我們也許最終會明白，生命是如何在冰雪覆蓋的地球上存活下來的

我們也許最終會明白生命是如何在冰雪覆蓋的地球上存活下來的

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.

生命在這塊藍色的大理石上攀爬時，曾面臨許多挑戰(zhàn);很多時候，它似乎已經(jīng)到了懸崖邊緣，但卻以驚人的活力卷土重來?，F(xiàn)在，研究人員終于弄清楚了生物是如何在被稱為“低溫期”的巨大冰川作用中幸存下來的。

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.

這個被稱為雪球的地球，從7.2億年前持續(xù)到6.35億年前。你可能會認為海洋上的一層冰，切斷了氧氣供應(yīng)，會阻礙動物生命的前進;但化石證據(jù)表明，情況并非如此。

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，生命存活了下來，然后在雪球地球之后綻放。根據(jù)這項新的研究，這是可能的，因為冰川融水在海洋中形成了含氧口袋。在這些綠洲中，化學(xué)合成生命可以等待冰河時代的到來，并在另一邊繼續(xù)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.

加拿大麥吉爾大學(xué)(McGill University)的沉積學(xué)專家麥克斯韋爾·萊赫特(Maxwell Lechte)解釋說：“證據(jù)表明，雖然在深度冰凍期間，由于缺氧，大部分海洋將不適合居住，但在被擱淺的冰蓋開始漂浮的地區(qū)，含氧融水的供應(yīng)是至關(guān)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."

“這種趨勢可以用我們所說的‘冰川氧泵’來解釋;冰層中的氣泡在融化時被釋放到水中，使其富含氧氣。”

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.

盡管那個時候的化石記錄非常非常少，但是有當時地球上的地質(zhì)條件的痕跡。沉積在海底的沉積物，特別是那些富含鐵的沉積物，使得萊克特和他的團隊能夠重建氧合水平。

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，人們認為生命一定以某種方式存在于地表的融水水坑中，但研究小組的發(fā)現(xiàn)表明了另一種方式。

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.

他們研究了三大洲的鐵建造——納米比亞的丘斯組、澳大利亞的尤德納穆塔納亞組和美國的金斯敦峰建造。

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.

總的來說，從冰川環(huán)境中的鐵同位素比率和鈰異常揭示了水大部分是極度缺氧的，但是越靠近冰架接地線，沉積物越氧化。

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.

任何生活在這些充氣水中的真核生物也需要食物才能茁壯成長。鐵可能是一個線索。

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.

我們知道海水中含有豐富的溶解鐵。我們知道，今天，存在著化學(xué)營養(yǎng)細菌，它們從溶解的鐵的氧化中獲取能量，當它們處理完鐵氧化物時，就會脫落。

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，冰架接地線周圍的氧化沉積物可能是由海洋中氧化鐵的細菌引起的，這些細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.

當然，我們沒有確鑿的證據(jù)來證明這一點，但這是一個符合現(xiàn)有證據(jù)的可信理論——它巧妙地掩蓋了關(guān)于雪球地球的幾個謎團。

"[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.

“(這項研究)不僅解釋了早期動物是如何在全球冰川作用下生存下來的，而且有力地解釋了在消失了十億多年之后，地質(zhì)記錄中鐵質(zhì)沉積的回歸，”麥吉爾大學(xué)的地球科學(xué)家蓋倫·哈爾弗森說。

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.

我們需要更多的研究來弄清楚這些環(huán)境是如何維持食物網(wǎng)的。在冰凍的極地地區(qū)存在著冰川生態(tài)系統(tǒng)和生態(tài)系統(tǒng)，它們支撐著今天驚人的生物多樣性;研究人員表示，這些地方可能是下一個值得研究的地方。

The research has been published in PNAS.

這項研究發(fā)表在《美國國家科學(xué)院院刊》上。