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“巨型”磁性细菌化石填补了地球气候历史的空白

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2021年02月02日

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"Giant" Magnetic Bacterial Fossils Fill In Gaps In The Earth's Climate History

“巨型”磁性细菌化石填补了地球气候历史的空白

Magnetic bacteria create compasses out of microscopic chains of orientated iron oxide so they can ride the Earth's magnetic field to better feeding grounds. They've been doing this for hundreds of millions of years, but at certain points in Earth's history, chains many times the size of modern versions appear – like finding the occasional titanosaur among lizards.

磁性细菌用微小的定向氧化铁链制造指南针,这样它们就可以利用地球的磁场去更好的觅食地。它们已经这样做了上亿年,但在地球历史的某些时刻,链的大小是现代版本的许多倍——比如在蜥蜴中偶然发现的雷龙。

Although still tiny by our standards, the larger versions are called giant magnetofossils by geologists and can help us reconstruct the Earth's climatic history. A new technique allows us to read this story more cheaply, and without having to destroy the magnetic fossils in the process.

虽然以我们的标准来看仍然很小,但更大的版本被地质学家称为巨磁化石,它可以帮助我们重建地球的气候历史。一项新技术使我们可以更廉价地阅读这个故事,而且在阅读过程中不必破坏磁性化石。

The early Eocene Epoch 56 million years ago is marked by magnetofossils some 20 times larger than those of other periods, although still just a 50th of the width of a human hair. The larger size is accompanied by compasses with shapes far more complex than the simple bars seen at other times. This sudden gigantism coincides with the last great surge in global temperatures (although still 170 times slower than modern times) the Paleocene Eocene Thermal Maximum. Similarly large magnetofossils also appeared during a less dramatic – but still substantial – subsequent warm spell, before disappearing again from the fossil record.

5600万年前的始新世早期的磁化石比其他时期的磁化石大20倍,尽管它的宽度只有人类头发丝的50倍。更大的尺寸伴随着比在其他时候看到的简单条形的圆规复杂得多的形状。这一突然的巨大变化与上一次全球气温急剧上升(尽管仍然比现代慢170倍)古新世始新世热最大值相吻合。类似的大磁化石也出现在随后的一段不那么引人注目的暖期——但仍然很重要——之后又从化石记录中消失了。

Stephen Luntz

Although we don't know why hot conditions allow magnetic fossils to so drastically increase in size, the relationship offers an opportunity for paleoclimatologists to spot other warm eras we may have missed in the geologic record. Unfortunately, to do so it has been necessary to extract the fossils from the sediments in which they are found. "The extraction process can be time-consuming and unsuccessful, electron microscopy can be costly, and the destruction of samples means that they are no longer useful for most other experiments," said University of Utah PhD student Courtney Wagner in a statement. "Collection and storage of these samples require specialized personnel, equipment and planning, so we want to preserve as much material for additional studies as we can."

虽然我们不知道为什么高温条件会让磁性化石的体积急剧增大,但这种关系为古气候学家提供了一个机会,让他们发现我们可能在地质记录中错过的其他温暖时代。不幸的是,要做到这一点,必须从发现它们的沉积物中提取化石。犹他大学的博士生考特尼·瓦格纳在一份声明中说:“提取过程可能是耗时和不成功的,电子显微镜可能是昂贵的,而且样品的破坏意味着它们不再适用于大多数其他实验。”“收集和储存这些样本需要专门的人员、设备和计划,所以我们希望尽可能多地保存材料,以便进行更多的研究。”

Wagner is part of a team that has announced a new method for studying magnetofossils in Proceedings of the National Academy of Sciences. Known as first order reversal curve (FORC) measurements, this allows them to distinguish giant magnetofossils from the more common sizes without impeding future research.

瓦格纳是一个研究小组的成员,该小组在《美国国家科学院院刊》上宣布了一种研究磁化石的新方法。这就是所谓的一阶反转曲线(FORC)测量,这使得他们能够在不阻碍未来研究的情况下从更普通的尺寸中区分巨磁化石。

Giant magnetofossils don't all have the same shape, often tapering at the ends. Image Credit: Courtney Wagner, Ioan Lascu, and Kenneth Livi

Wagner and co-authors applied FORC to layers of sediment taken from Wilson Lake, New Jersey, confirming the presence of giant magnetofossils coinciding with global hothouse events. The organisms that make them are still unknown, their cells not fossilizing like the metal they deposit, but the authors hope FORC may help us solve this mystery too.

Wagner和他的合著者将FORC应用于新泽西州威尔逊湖的沉积层,证实了与全球温室事件相一致的巨磁化石的存在。制造它们的生物体仍然未知,它们的细胞不像它们沉积的金属那样变成化石,但作者希望FORC也能帮助我们解开这个谜。

The same edition of the journal contains another paper describing a way to read far more ancient climate records, dating back to before the first shelled animals. The ratio of oxygen isotopes in carbonate mud reveals the temperatures at the time it was deposited, they show, just as more recent temperature fluctuations are revealed from the isotopes in marine shells. From this, the researchers established that during the Cambrian Era – when animals were first truly establishing themselves – cooler periods were associated with the flourishing of animals, while warmer interludes saw microbial life strike back.

该杂志的同一版还包含了另一篇论文,描述了一种阅读更古老的气候记录的方法,可以追溯到第一种有壳动物出现之前。他们指出,碳酸盐岩泥浆中氧同位素的比例揭示了它沉积时的温度,就像海洋贝壳中的同位素揭示了更近期的温度波动一样。由此,研究人员得出结论,在寒武纪,也就是动物们第一次真正建立自我的时期,寒冷的时期与动物的繁盛有关,而温暖的时期则见证了微生物的反击。


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