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Many people know about the long history of life on Earth: over the course of 3.8 billion yearsOrganisms have evolved from prokaryotes to eukaryotes, from single-celled eukaryotes to multicellular eukaryotes, and gradually evolved from simple life to complex life. On the earth today, animals, terrestrial plants, fungi and macro-body algae, including humans, are all complex life forms and multicellular eukaryotes.
Living phylogenetic tree (Wikipedia).
So, when did multicellular eukaryotes emerge on Earth? This is one of the major pivotal events in the history of the evolution of life. Previous studies have proven that this time is 15 years ago600 million years ago. Could it be earlier?
On January 25, 2024, the "Early Evolution of Earth-Life Systems" team led by Zhu Maoyan, a researcher at the Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, answered this question. Team member Miao Lanyun, Ph.D., Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences, in the Yanshan area of North China 16Fossils of multicellular eukaryotes have been found in strata 300 million years ago, and these microfossils with exquisite cellular structures are believed to be the earliest fossil records of multicellular eukaryotes found in the world so far. The results were published in the latest issue of the journal Science Advances (click "Read the original article" at the end of the article).
Are the fossils I found the earliest multicellular eukaryotes? How does this proof question work?
At the foot of the Great Wall, there are secrets of the early evolution of life
Researchers in the field of Yanshan (**Author provided).
Yanshan Mountain Range is one of the important mountain ranges in northern China, located in the south of the Bashang Plateau in Inner Mongolia, north of the Hebei Plain, east of the Baihe Valley, and west of Shanhaiguan.
Why did the research team set their sights on this? What everyone doesn't understand is,For geology and paleontology, the Yanshan Mountains have even more extraordinary significance.
At the foot of the Great Wall, there is a set of rocks called "Great Wall System" and "Jixian System", which are Cambrian sedimentary strata from 1.8 billion to 1.3 billion years ago, nearly 10,000 meters thick, and are one of the best and most classic areas in the world to carry out the early geological history and life evolution of the earth, represented by the Jixian (now known as Jizhou) area of Tianjin. In 1984, China established the first national nature reserve in Jixian County, Tianjin, and in 2001, Tianjin Jixian National Geopark was established, which records the natural scenery, cultural monuments and unique geological records of Yanshan.
The Middle and Upper Proterozoic stratigraphic section of Jizhou District records the geological evolution history here (**Provided by the author).
In the early 30s of the 20th century, Gao Zhenxi, an academician of the Chinese Academy of Sciences, and others established a standard section of the "Sinian system" in Jixian County, Tianjin, at the foot of the Great Wall. Over the past 100 years, generations of geologists have studied and their time has become more and more precise.
In 1997, Zhu Shixing and Huang Xueguang of the Tianjin Geological Survey Center of the China Geological Survey carried out field geological survey work in the Qianxi and Kuancheng areas of Hebei Province600 million years ago, large carbonaceous membrane fossils were found in the Gaozhuang Formation of the "Jixian system", which is a layer of dark carbonaceous material that is flattened and preserved in the process of fossilization after the organism is buried.
Higher than the Zhuang Formation macro-body carbonaceous membrane fossil (**Author provided).
In 2016, Zhu Maoyan's team, together with Zhu Shixing and other scholars at home and abroad, carried out a systematic study on these specimens, and believed that they belonged to multicellular eukaryotic fossils, 15 years ago600 million years. Moreover, this batch of multicellular eukaryotic fossils has grown "very large", up to 8 centimeters wide, and the incomplete fossils are up to 30 centimeters long. The appearance of such large macrofossils indicates that there will be a relatively simple microfossil (i.e., the kind that is invisible to the naked eye) before this. This result breaks through the previous scientific understanding, not only advanced the emergence time of large multicellular eukaryotes on Earth by nearly 1 billion years from the previously thought 600 million years ago, but also infers that the time of multicellularization of eukaryotes should be earlier.
In order to verify this inference of her predecessors, Miao Lanyun has been searching for multicellular eukaryotic fossil records in the Late Paleoproterozoic "Great Wall" strata in the Yanshan area earlier than 1.6 billion years since her doctoral studies.
Eight years of accumulation, every experiment is "opening the blind box".
Because most of the fossils in the Great Wall strata are microfossils that are invisible to the naked eye, and the details can only be seen clearly with the help of a microscope, and these fossils are deeply embedded in the shale, researchers have to bring the collected samples back to the laboratory and find the microfossils for analysis through rigorous microfossilic acid extraction experiments. For eight years, Miao Lanyun has been traveling back and forth between Nanjing and Hebei: collecting samples at the foot of Yanshan Mountain and returning to her laboratory in Nanjing.
Rock samples were collected (**provided by the author).
The reason why it is said to be "unpacking the blind box" is because not all shales have microfossils preserved, and the results of each microfossil acid extraction experiment are unpredictable
The process of "unpacking the blind box" is:
1) First of all, hydrofluoric acid is used to dissolve all the minerals in the shale, and the organic matter (mainly composed of carbon and hydrogen) is not affected by hydrofluoric acid because it can be retained;
2) Caf2 is produced during the previous step, which is a flocculent substance that makes the solution look cloudy like milk. In order to remove CaF2, hydrochloric acid is added after the residual hydrofluoric acid is removed, and then the flocculent CaF2 is removed by heating in a water bath.
3) The remaining solution is mainly hydrochloric acid, water and organic matter, and then the solution is washed to neutral by changing the water, and finally the remaining solution is mainly water and organic matter.
Fossils are formed and preserved in organic matter, so when looking for microfossils, we must look for them in organic matter.
Microfossil extraction experiment (**Provided by the author).
Microscopic topography analysis of fossils (**Author provided).
The paleontological version of the "blind box" looks something like this:
Samples treated with acid extraction (**Provided by the authors).
Teach you to identify fossils of multicellular eukaryotes
Finally, Miao Lanyun found it from the hundreds of samples collected278 micro-multicellular eukaryotic fossil specimens with beautifully preserved cell structuresThese specimens are from the middle and upper strata of the Chuanlinggou Formation in the Wengjiazhuang section of Kuancheng County, Hebei Province.
You may be wondering, the above samples all look similar, how can you tell which ones are multicellular eukaryotes? Let's analyze the characteristics of multicellular eukaryotic fossils in combination with **.
Figure 1The magnificent green algae found in the Kuanlinggou Formation. The fossil is preserved as a multicellular filament composed of organic matter walls, showing changes in filament morphology caused by changes in cell size. The diameter of the filamentous body shrinks to one end (a-d, f-i, k), the diameter of the filamentous body remains unchanged (j), and the filamentous body (e, l) with the intact end is preservedScale bars for F-H and K represent 100 μm, and the rest represent 50 μm (Miao et al.)., 2024b）
Figure 2Magnificent green algae with spore structure. Scale bars for a, c, d, and f represent 50 μm (Miao et al.)., 2024b）
The first feature: large cells.
Under the microscope, it can be seen that these fossils are made up of giant cells. They are unbranched filaments composed of a single row of cells (Figures 1 and 2) ranging from 20-190 μm in diameter and up to 860 μm in length without an outer sheath. (Note: Prokaryotic cells are generally smaller than 2 μm; Eukaryotary cells are generally 2-100 μm).
The second feature: the morphology shows a certain complexity.
Some of these fossils have filamentous bodies that remain the same in diameter, and the cells are short columnar to long columnar; Some filaments shrink uniformly toward one end, and the cells are columnar, barrel-shaped, or cup-shaped; Some filaments are tapered at only one end (Figure 1). By measuring different types of multicellular filaments that show a continuous transition in morphology, the researchers found that these fossilized multicellular filaments belong to the same species.
The complexity of these fossils is also reflected in the fact that some of the fossils have been found to have circular structures similar to living reproductive cells, spores, suggesting that the fossils are actually spores-reproducing organisms.
Through literature research, Miao Lanyun found that the morphology and size of the filamentous fossils are similar to the "Qingshania magnifica yan" (1989) found in the Chuanlinggou Formation in Jixian County, Tianjin before 1989, so these haveGiant cells with complex cell morphologyThe fossil should be the "magnificent green algae".
If you have giant cells and complex morphology, must you be a multicellular eukaryotic organism? There are still a few "screening questions" to be done.
If these conditions are met, the identity of "Magnificent Green Algae" is confirmed
To determine the identity of this fossil, it is necessary to compare it with living organisms and contemporaneous organisms.
1.Comparison with living creatures
Among living organisms, there is a very wide variety of filamentous organisms consisting of a single row of cells, which are widespread in both prokaryotes (bacteria and archaea) and eukaryotes. Researchers have based on the fossils found this timeGiant cells and complex filamentous morphologyThis feature begins to be excluded**.
The researchers first compared the magnificent green algae with the living prokaryotes. According to statistics, the currently known prokaryotic filaments are distributed in at least 147 genera in 12 phyla, and there is no type of prokaryotes that can be similar to that of Magnificent Qingshan algae by comparing the morphological complexity, cell size and reproduction mode of filaments. Most of these living prokaryotic filaments are small, while some of the larger organisms are relatively simple. Therefore,Exclusion of magnificent green algae is prokaryotes
Among the living eukaryotes, there are many filamentous organisms that resemble the magnificent green algae, for example: heterotrophic filamentous fungi and filamentous oomycetes, especially most eukaryotic algae contain filamentous bodies, such as brown algae, yellow algae, green algae, red algae, wheel algae, cococcus, etc.
Magnificent green algae are similar to heterotrophic filamentous fungi and filamentous oomycetes, especially most eukaryotic algae contain filamentous bodies, such as brown algae, yellow algae, green algae, red algae, wheel algae, cococcus cococcus, etc. (**Author provided).
The contrast between the magnificent green algae and some living green algae is close.
Courtesy of the author).
The comprehensive analysis showed that the algal filament morphology, cell size distribution and reproduction mode of some existing green algae were the most similar. Therefore,The research team believes that Magnificent Qingshan is a fossil of multicellular eukaryotic organisms, and it is likely to be a multicellular algae with the metabolic ability of photosynthesisHowever, it is not currently possible to attribute it to a specific living category.
2.With the help of high technology, compare with "peers".
In order to further verify the eukaryotic properties of S. magnificia, the research team used laser Raman spectroscopy to compare the organic matter composition of three species of cyanobacteria (multicellular prokaryotes) extracted from the same shale sample.
Raman spectroscopy showed that compared with the multicellular prokaryotes of the same level, Algae magnificus underwent low-level metamorphism (metamorphism refers to changes in the original material structure or composition due to temperature, pressure or other factors). For geological samples, after a long period of geological processes, such as geothermal gradients and pressures, its original material structure and composition will gradually change), and it is unlikely to be modern biological pollution. Moreover, the organic matter composition of the fossils is significantly different from that of cyanobacterial fossilsFurther support for the interpretation of multicellular eukaryotic properties.
eukaryoticFinally, a common ancestor
The time of origin may be earlier
The fossil-bearing strata found this time have a layer of volcanic tuff at the top, which has been dated by zircon uranium-lead isotopes and the result is 163.5 billion, which provides a direct age constraint for newly discovered fossils. Therefore, "Magnificent Qingshan Algae" is considered to be the earliest fossil record of multicellular eukaryotes found in the world to date. 16300 million years ago!
Based on the above "proof question" process, the researchers can determine that the magnificent green alborus is the earliest multicellular eukaryotic fossil with a cellular structure (16300 million years ago), and may be an extinct eukaryotic algae (exact relationship unknown).
Because the earliest fossil record of eukaryotes (single-celled eukaryotic fossils) that is generally accepted by the academic community is found in North China and northern Australia about 16 years ago500 million years old in the Late Paleoproterozoic strata. The magnificent green algae appeared only slightly later than these oldest single-celled eukaryotic fossilsThis indicates that after the emergence of eukaryotes, complex multicellular evolution has rapidly undergone.
Since eukaryotic algae (panchromosome plants) belong to a clade of crown eukaryotes (modern eukaryotes), if Magnificent Aoyama algae can be identified as eukaryotic algae that are responsible for photosynthesis, thenThe last common ancestor of eukaryotes (LECA) should be no later than 16300 million years ago! , nearly 600 million years ahead of the time generally accepted by the current academic community. This provides new thinking for further revealing the mystery of the origin and early evolution of complex life, as well as the evolution of the Earth's environment in the Proterozoic.
Simplified diagram of eukaryotic phylogenetic tree and early important fossil record of eukaryotes. In the eukaryotic tree, the dotted line represents the stem group of eukaryotes, and the solid line represents the crown group of eukaryotes (the last common ancestor of eukaryotes, Leca, and all its descendants).The light gray bands on the divergence points indicate the divergence time estimated by the molecular clock (Parfrey et al.)., 2011, pnas）.The figure on the right shows the earliest fossil record of various groups of eukaryotes (according to Miao et al, revised 2024b).
Professor Andrew Knoll of Harvard University and Qu Yuangao, a researcher at the Institute of Deep-Sea Science and Engineering of the Chinese Academy of Sciences, participated in the research on the results.
The research was jointly funded by the National Key R&D Program of China (2022YFF0800100), the National Natural Science Program of China (41888101, 41921002, 41972204), and the Interdisciplinary Innovation Team of the Chinese Academy of Sciences (JCTD-2020-18).
Related**:
1]miao, l., moczydłowska, m.*,zhu, s., zhu, m.*,2019. new record of organic-walled, morphologically distinct microfossils from the late paleoproterozoic changcheng group in the yanshan range, north china. precambrian research, 321:172-198.
2]miao, l., yin, z., li, g., zhu, m.*,2024a. first report of tappania and associated microfossils from the late paleoproterozoic chuanlinggou formation of the yanliao basin, north china. precambrian research, 400:107268.
4]miao, l., yin, z., knoll, a.h., qu, y., zhu, m.*,2024b. 1.63-billion-year-old multicellular eukaryotes from the chuanlinggou formation in north china. science advances.
5]zhu, s., zhu, m.*,knoll, a.h., yin, z., zhao, f., sun, s., qu, y., shi, m., liu, h., 2016. decimetre-scale multicellular eukaryotes from the 1.56-billion-year-old gaoyuzhuang formation in north china. nature communications, 7:11500.
Topic Selection Review |Somerset.
Copywriting |Somerset, Miao Lanyun, Zhu Maoyan, Zhu Pengfei.
Typography Editing |Zhu Pengfei.
Research Progress |Scientific research progress in the discovery of the world's earliest multicellular eukaryotic fossils in the Yanshan areaThe earliest typical fossil of eukaryotes discovered for the first time in the Yanshan area, Tappania Interview with Zhu Maoyan: It took 31 years to "travel" through the Cambrian and strive to solve Darwin's puzzle.
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