“False” Microfossils Challenge our Interpretation of the Fossil Record
A new study by an international team of scientists has found that the presence of non-microbial “false” microfossils in early Earth sediments may challenge our current understanding of the early evolution of life.
在地球历史的大部分时间里, 生命仅限于微观领域, with bacteria occupying nearly every possible niche. Life is 一般 thought to have evolved in some of the most extreme environments, like hydrothermal vents deep in the ocean or hot springs that still simmer in Yellowstone. Much of what we know about the evolution of life comes from the rock record, which preserves rare fossils of bacteria from billions of years ago. But there is still uncertainty in whether or not a purported fossil is indeed a trace of life, and the field is plagued by “false positives”.
现在发表在 地质, researchers have found evidence that could help settle these arguments over which microfossils are signs of early life and which are not. They have shown that biomorphs – fossilised spheres and filaments made of organic carbon and similar in shape to bacterial fossils— can form without life’s influence, and might even be easier to preserve in rocks than bacteria.
图1. Spherical and filamentous “false” microfossils made of organic carbon and sulphur. 图片由朱莉Cosmidis提供.
Biomorphs were accidentally discovered while mixing organic carbon and sulfides in the laboratory; spheres and filaments were forming in experiments and at first were assumed to be the result of bacterial activity. “非常早期的, we noticed that these things looked a lot like bacteria, 无论是化学上还是形态上, 但实际上是非生物形成的,首席调查员说 朱莉Cosmidis 澳彩教授. “We thought, ‘What if they could form in a natural environment? 如果它们可以保存在岩石中呢?’ We have to try that, to see if they can be fossilised” she added.
第一作者, 克里斯汀年来, of the University of Michigan said “They start just looking like a residue at the bottom of the experimental vessel, 但是在显微镜下, you could see these beautiful structures that looked like bacteria. And they formed in these very sterile conditions, so these stunning features essentially came out of nothing. 这真是令人兴奋的工作.”
然后进行新的实验, testing to see if these abiotic “organic envelopes” could be fossilised in rocks, 就像细菌一样. 通过在结构中加入二氧化硅, they aimed to recreate the formation of chert, a silica-rich rock that commonly preserves early microfossils. The ‘fossilisation’ progress was constantly tracked in glass vessels. It was found that not only could the biomorphs be fossilised, but also that they were much easier to preserve than bacterial remains. These strong carbon-sulfur structures were more resilient and less likely to flatten out than their fragile biological counterparts.
图2. This “false” organic microfossil is morphologically similar to twisted filamentous bacteria. 图片由朱莉Cosmidis提供.
“Microbes don’t have bones,” Cosmidis explained. “它们没有坚硬的皮肤或骨骼. 它们只是黏糊糊的有机物. 为了保护它们, you need to have very specific conditions”—like low primary productivity and rapid sediment deposition—“so it’s kind of rare when that happens.”
在一个层面上, their discovery complicates things: knowing that these shapes can be formed without life and preserved more easily than bacteria casts doubt, 一般, 在澳彩早期生活的记录上. 但是有一段时间, geobiologists have known no better than to rely solely on morphology to analyse potential microfossils. 他们现在带来了化学反应, 太: the authors showed that these pseudo-microfossils may be chemically distinguished from bacteria based on their organic composition.
The organic objects that Nims created were formed in a high-sulfur environment, replicating conditions on early Earth (and some hot springs today). 黄铁矿, 或者“傻瓜的金子”,” is an iron-sulfide mineral that would likely have formed in such conditions, so its presence could be used as a beacon for potentially problematic microfossils. “If you look at ancient rocks that contain what we think are microfossils, 它们通常还含有黄铁矿,科斯米迪斯说. “For me, that should be a red flag: ‘Let’s be more careful here.’ It’s not like we are doomed to never be able to tell what the real microfossils are. 澳彩只需要在这方面做得更好.”
This work won’t only help scientists understand Earth; the same processes likely happened on Mars, 太. 《澳彩》, if it ever existed—or exists now—was probably microbial, so we’ll have to learn to recognise microbial life in Martian rocks”, Cosmidis说.
The study “Organic biomorphs may be better preserved than microorganisms in early Earth sediments” has been published in 地质 on January 27th, 2021. DOI: http://doi.org/10.1130/G48152.1
Article adapted from the 地质 press release by Rebecca Dzombak. 你可以在这里阅读完整版.