最古老的陆地化石可以解释地球是如何从雪球州恢复过来的

最古老的陆地化石可以解释地球是如何从雪球州恢复过来的

Thread-like filaments, attached to hollow spheres in 635 million-year-old rocks, represent the earliest evidence we have of life on land. They may also help explain how life rebounded from “Snowball Earth”, the periods when it was so cold even much of the equator was covered in ice.

在6亿3千5百万年前的岩石中，丝状的细丝附着在空心球体上，这是我们拥有的陆地上有生命的最早证据。它们也可能有助于解释生命是如何从“雪球地球”中恢复过来的。在“雪球地球”时期，地球非常寒冷，甚至赤道的大部分地区都被冰雪覆盖。

The upper parts of the Doushantuo Formation in South China have provided an abundance of fossils, but the older ones were thought to predate anything of interest. Virginia Tech PhD student Tian Gan only stumbled across a set of preserved branching filaments and hollow spheres close to the formation's base by chance. "It was an accidental discovery," Gan said in a statement.

中国南方陡山沱组的上部已经提供了大量的化石，但更古老的化石被认为比任何有趣的东西都要早。弗吉尼亚理工大学的博士生田甘(音译)只是在岩层底部偶然发现了一组保留下来的分支细丝和空心球体。甘在一份声明中表示:“这是一个意外发现。”

The only thing the filaments truly resemble is modern-day fungi, and the authors think that's probably what they were. Wherever it fits on the tree of life, however, Gan thinks it may explain one of paleontology's big questions: how did life rebound so quickly after being almost wiped out by snowball Earth?

这些丝状物唯一真正相似的是现代的真菌，而作者认为这可能就是它们曾经的样子。然而，甘认为，无论它与生命之树的哪个位置相吻合，它都可以解释古生物学的一个大问题:在几乎被雪球地球毁灭的情况下，生命是如何迅速复苏的?

Stephen Luntz

Snowball Earth was not like more recent ice ages. The ice was so thick and universal we are unsure how any life survived at all, making the sudden appearance of the Ediacaran diversity soon after the world warmed a mystery.

雪球地球不像更近的冰河时代。冰层如此之厚，如此普遍，我们不确定生命是如何存活下来的，这使得在世界变暖后不久突然出现的埃迪卡拉多样性成为一个谜。

Gan's discovery may answer that. “We realized that this could be the fossil that scientists have been looking for a long time. If our interpretation is correct, it will be helpful for understanding the paleoclimate change and early life evolution," Gan said.

甘的发现或许可以回答这个问题。“我们意识到这可能是科学家们已经寻找了很长时间的化石。如果我们的解释是正确的，这将有助于理解古气候变化和早期生命进化，”甘说。

In Nature Communications, Gan advances the theory fungi broke down rocks until the nutrients they contained washed to the sea, fertilizing the post-snowball era.

在《自然通讯》中，甘提出了真菌分解岩石的理论，直到岩石中含有的营养物质被冲到海里，成为后斯诺鲍时代的肥料。

"Fungi have a mutualistic relationship with the roots of plants, which helps them mobilize minerals, such as phosphorus,” Gan explained.

“真菌与植物的根有一种互惠关系，这有助于它们调动矿物质，如磷，”甘解释说。

"The question used to be: 'Were there fungi in the terrestrial realm before the rise of terrestrial plants'," said co-author Professor Shuhai Xiao "And I think our study suggests yes. Our fungus-like fossil is 240 million years older than the previous record. This is, thus far, the oldest record of terrestrial fungi."

“过去的问题是:‘在陆生植物出现之前，陆生领域中是否存在真菌?’”合著者肖树海教授说，“我认为我们的研究表明存在。”我们发现的类真菌化石比之前的记录早了2.4亿年。这是迄今为止最古老的陆生真菌记录。”

Fungus or not, the fossil appears to have lived in sheet cavities in the dolostone rocks in which it was found, but Xiao acknowledged; “Little is known about how exactly they lived and how they were preserved. Why can something like fungi, which have no bones or shells, be preserved in the fossil record?" The spheres may be part of the same organism, or something else with which the fungus had a symbiotic relationship.

不管是不是真菌，这具化石似乎生活在发现它的白云岩的片状洞里，但肖承认;“他们究竟是如何生活的，又是如何被保存下来的，我们知之甚少。为什么像真菌这样既没有骨头也没有壳的生物，能在化石记录中保存下来呢?”这些球可能是同一生物体的一部分，或者是与真菌有共生关系的其他东西。

The cavities were sealed shut with natural cement 632 million years ago, which the authors believe rules out more recent colonization of the space.

这些空腔是6.32亿年前用天然水泥封起来的，作者们认为这排除了最近在太空中殖民的可能性。

Molecular clocks indicate the last common ancestor of fungi and other forms of life lived 900-1,500 million years ago, but this is presumed to have been in the oceans. It's been a mystery when a descendent on the fungal line first had the bright idea of taking over the land. A few candidates for terrestrial fungi of immense age have been found, but these were in estuary sediments, and could as easily have lived on location as been washed off the land.

分子钟表明，真菌和其他生命形式最后的共同祖先生活在9亿至15亿年前，但据推测，这是在海洋中。当真菌系的一个后代第一次有了接管土地的聪明想法时，这一直是个谜。人们已经发现了一些年代久远的陆生真菌的候选者，但这些真菌都存在于河口的沉积物中，它们既可以轻易地从陆地上被冲走，也可以轻易地在当地生存。