“巨型”磁性細菌化石填補了地球氣候歷史的空白

“巨型”磁性細菌化石填補了地球氣候歷史的空白

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.

磁性細菌用微小的定向氧化鐵鏈制造指南針，這樣它們就可以利用地球的磁場去更好的覓食地。它們已經(jīng)這樣做了上億年，但在地球歷史的某些時刻，鏈的大小是現(xiàn)代版本的許多倍——比如在蜥蜴中偶然發(fā)現(xiàn)的雷龍。

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.

雖然以我們的標準來看仍然很小，但更大的版本被地質(zhì)學家稱為巨磁化石，它可以幫助我們重建地球的氣候歷史。一項新技術(shù)使我們可以更廉價地閱讀這個故事，而且在閱讀過程中不必破壞磁性化石。

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.

5600萬年前的始新世早期的磁化石比其他時期的磁化石大20倍，盡管它的寬度只有人類頭發(fā)絲的50倍。更大的尺寸伴隨著比在其他時候看到的簡單條形的圓規(guī)復雜得多的形狀。這一突然的巨大變化與上一次全球氣溫急劇上升(盡管仍然比現(xiàn)代慢170倍)古新世始新世熱最大值相吻合。類似的大磁化石也出現(xiàn)在隨后的一段不那么引人注目的暖期——但仍然很重要——之后又從化石記錄中消失了。

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."

雖然我們不知道為什么高溫條件會讓磁性化石的體積急劇增大，但這種關(guān)系為古氣候?qū)W家提供了一個機會，讓他們發(fā)現(xiàn)我們可能在地質(zhì)記錄中錯過的其他溫暖時代。不幸的是，要做到這一點，必須從發(fā)現(xiàn)它們的沉積物中提取化石。猶他大學的博士生考特尼·瓦格納在一份聲明中說:“提取過程可能是耗時和不成功的，電子顯微鏡可能是昂貴的，而且樣品的破壞意味著它們不再適用于大多數(shù)其他實驗。”“收集和儲存這些樣本需要專門的人員、設(shè)備和計劃，所以我們希望盡可能多地保存材料，以便進行更多的研究。”

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.

瓦格納是一個研究小組的成員，該小組在《美國國家科學院院刊》上宣布了一種研究磁化石的新方法。這就是所謂的一階反轉(zhuǎn)曲線(FORC)測量，這使得他們能夠在不阻礙未來研究的情況下從更普通的尺寸中區(qū)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和他的合著者將FORC應用于新澤西州威爾遜湖的沉積層，證實了與全球溫室事件相一致的巨磁化石的存在。制造它們的生物體仍然未知，它們的細胞不像它們沉積的金屬那樣變成化石，但作者希望FORC也能幫助我們解開這個謎。

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.

該雜志的同一版還包含了另一篇論文，描述了一種閱讀更古老的氣候記錄的方法，可以追溯到第一種有殼動物出現(xiàn)之前。他們指出，碳酸鹽巖泥漿中氧同位素的比例揭示了它沉積時的溫度，就像海洋貝殼中的同位素揭示了更近期的溫度波動一樣。由此，研究人員得出結(jié)論，在寒武紀，也就是動物們第一次真正建立自我的時期，寒冷的時期與動物的繁盛有關(guān)，而溫暖的時期則見證了微生物的反擊。