1 Introduction
PaleoChemistry is an interdisciplinary field combining chemistry and Paleology, which includes the study of Ancient Objects and their subordinate branches, such as Paleontology, Archeology, Palaeoanthropology, etc. This paper focuses on "Paleontology + Chemistry", focusing on the situation of Paleontology at that time, the process of fossil formation, and the Chemistry and changes of the entity and its adjacent surrounding rocks. Based on the thinking of "Look into the Bone and Cell", this paper explores the internal and external composition and changes of fossils, trying to understand what happened when paleontology was alive, when it died and after a long period of time, and then to understand the evolution of life on Earth. It goes into paleontological fossils from another angle and provides a more complete content, which is detailed in the An Introduction to PaleoChemistry of the Introduction to Paleobiochemistry
[1].
Chemistry, the study of matter in the universe and its transformation; The familiar chemical reaction formula refers to the process from "Reactants" to "Products" under a certain "Condition". The chemical reaction formula expresses the change of substances.
Interestingly, the Chinese translation of the word Fossil is "Fossil", which not only uses the word "fossil", but also essentially explores the product of paleontological Petrification, trying to understand the possible situation of paleontology and its environment, life evolution and so on. However, current paleontological research methods usually focus on and are limited to describing taxonomic features from the outside, but rarely from the inside. In the hands of paleontologists, only the last incomplete "product" of chemical reactions-fossils, and many of the essence and characteristics of the original organisms, that is, the reactants, are usually or almost not completely preserved. There is little or no information about the "reaction conditions" in the middle. At most, they can only be inferred from the incomplete "products", but can not be clearly understood or controlled. After all, the formation conditions of fossils are often geological changes of millions or even hundreds of millions of years.Unable to replicate in the laboratory, it can only be inferred and guessed that it is impossible to be completely sure. Most (99%) of the organisms that once lived on the earth have been extinct. Only the very lucky ones have fossils preserved. In terms of the number of individuals, it is estimated that the probability is one in a thousand to one in ten thousand. Many species, such as many microorganisms and mollusks, have little chance of forming fossils, so how they are can only be imagined and speculated, and their reliability can not be predicted.
To study paleontology, we must start from the direction of paleontology, go deep into fossil bones and cells, and explore what changes have taken place in the chemical composition and fine structure of paleontology over a long period of time? What is preserved today? For example, it is a common phenomenon to preserve organic residues in solid fossils, so what is the chemical Mechanism for preserving these organic residues? What role does condensed matter chemistry play? In short, paleobiochemistry is the study of the "transformation" of paleontology from before life and after death to the present.
Because this is an unprecedented new discipline, we try to make systematic integration here. In terms of chemistry, this paper attempts to explore the most basic and fundamental mysteries related to paleontology from the perspective of condensed matter chemistry. For example, it is generally believed that fossils are ancient organisms that have changed into stones, from organisms to inorganic minerals, and organisms cannot be preserved for tens of millions of years. However, our team found preserved Native Collagen I in the bones of Lufengosaurus embryos 200 million years ago
[2,3]. This paper gives three examples to illustrate. Condensed matter chemical reactions, which certainly play a key fundamental mechanism in paleobiochemistry, await our revelation.
2 Fossil formation
Figure 1 shows the possible path of an organism from "Life" to becoming a "Discovery" fossil, in which all the changing factors, namely "reaction conditions",Any one of them may affect the condition of the final fossil found, especially from the perspective of paleontology, almost every change factor may cause the chemical differences related to the examination of fossils, that is, the parameters of chemical changes over hundreds of trillions of years
[4]. For details, see Section 1, Chapter 3 of Ref.
In this long journey of reaction "conditions", the starting point is an organism with many very complex biochemical components, and many factors in the map will affect the chemical changes and chemical composition of fossils and adjacent surrounding rocks. In the long time, how many times have there been geological changes? Water quality at different pressure and temperature? Are constantly reacting chemically with fossils and adjacent country rocks; That is to say, from birth to death to fossil, it is actually a very complex and often difficult to determine the "condition" change system, and it is difficult to determine what the reaction "condition" mentioned above is. Moreover, not all fossils are equally well preserved, and if proteins or other soft tissues are to be preserved, they must be protected from too much external influence, with very little water flow, and be protected from microbial attack. The quality of preservation is also affected by how long one usually lies on the surface of the deposit after death. Soft tissues in rapidly buried bones are better preserved than those exposed for a long time. However, for large animals, such as sauropod dinosaurs, rapid burial may be difficult, while small animals may be quickly buried as a whole. In addition, the type of bone also affects the preservation of organic residues, and the compact bone cortex of large animals is more easily preserved than the usually fragile skull components, or the delicate bones of small animals.
3 Detection method
3.1 in situ in loco Multiple Examination
Before doing the sample to discuss the experimental process, we should first deal with the sample. In the process of sample preparation, several serious questions must be considered in each sample treatment process: Will the physical methods or chemical agents used in the treatment process destroy the fossil or cause chemical changes? Was there any chemical change that went unnoticed so that subsequent analysis gave the wrong result?
Sample preparation, such as using the popular Focus Ion Beam (FIB), can cut very accurately and thinly, but it should also be considered that under the high-energy Ion Beam, the organic matter will be burned long ago? Please see Figure 2. This is a Paleoproterozoic fossil sample. In order to perform three-dimensional Raman scanning, the operator first used a focused ion beam to "gently" smooth the surface. Through the three-dimensional Raman scanning image, it can be seen that the focused ion beam burned off a lot of organic residues.
Paleobiochemical analysis should use all possible non-destructive analyses first, and destructive tests as a last resort. Fig. 3 shows the results of overlapping images of four different illumination sources at the same position of the same sample, from top to bottom: FTIR, Multiple Harmonic Genera-tion Microscopy (MHGM), general optics, and Neutron Tomography; This means that multiple different detection methods can be used at the same location of the same sample to obtain multiple information at the same location for research and analysis. The "in situ isotopic multiplex detection (in situ in loco multiple examinations)" proposed here is of great significance to paleobiochemistry. It is not only non-destructive, but also obtains multiple data from the same specimen, and can superimpose a variety of non-destructive detection images. It can integrate multiple data of the same fossil and the same detection point to obtain more complete information, which is a very meaningful research method.
3.2 Chemical Morphology
In biological and paleontological conventions, the morphological description of an organism is a critical part of the identification of a fossil organism. However, in the process of fossilization, the morphology of the original organism has changed to varying degrees and the chemical composition has changed
[5][6]. Paleobiochemistry, by providing three-dimensional chemical forms of the fossil itself and its surrounding rocks, opens up new ways to "see into the bone and cells" to more fully explore the comprehensive information of an organism before and after death
[7]. Many chemical analyses are very destructive, and samples must be ground into thin slices or dissolved in chemical reagents before chemical analysis can be carried out
[8]. The in situ isotopic multiple detection and three-dimensional chemical morphology proposed here are shown in the femur of Lufenglong embryo in Fig. 4. Fig. 5 is a screenshot of the 2.2 billion year-old Xiaoxiamiliang Mountain (Xiaoxiamiliang Mountain, Eukaryotic Domain, Huangxin, New Species, Liangshania shrimpy Huang gen. et sp. nov. 2021) unearthed in Daqing, Yunnan Province, showing the three-dimensional distribution of chemical components in these two different body fossils. Ideally, all nondestructive tests should be performed to obtain internal histologic and chemomorphologic information, and only then should destructive analysis be performed.
Fig. 4 is a Raman-CT image of the chemical composition in the fossil bone of Lufenglong embryo, in which the blue is the apatite group represented by the phosphate peak in the fossil bone, the green is the carbonate represented by the carbonate peak, and the red is the type I collagen represented by the amide III peak. It can be clearly seen from the figure that the Carbonate does not go too deep, about less than half the depth from the surface, which is consistent with the "Carbonate Cementing" mentioned in the second example. Carbonate forms a cement layer that does not go very deep into the fossil, which is called carbonate cementation.
Fig. 5 is a Raman tomography of the mountain of the oldest multicellular eukaryote Xiaoxiami. From mass spectrometry analysis, it is known that the fossil preserves 18 basic amino acids, and through non-destructive X-ray fluorescence (XRF) analysis, it is known that iron, titanium, manganese and barium metal ions are enriched in the fossil body, which should form some kind of combination with those amino acids. The results show that organic and inorganic substances are closely mixed and sandwiched together, rather than existing independently.
4 Case Example
This paper describes three examples of organic residues preserved in fossils and attempts to explore the role of condensed matter chemistry in fossils: (1) the preservation of type I collagen in the bones of dinosaurs and dinosaur embryos about 200 million years ago; (2) The universality of organic residues preserved in solid fossils, and the discussion of Carbonate Cementing preservation; (3) combination of metal ion with protein/peptide/amino acid. With these three examples as an introduction, we hope to further understand the mystery of condensed matter chemistry behind these interesting facts that violate "common sense" at first glance.
4.1 About 200 million years ago, dinosaurs and dinosaur embryos preserved type I collagen in their bones
"Dinosaur Embryology" is a new field in the field of dinosaurology established by the discovery of the world's oldest Dinosaur embryo fossils in 2003. Through the research policy of "looking into the bone" and using various advanced scientific research instruments and methods (Fig. 6-8), we can deeply understand why the embryonic development process of dinosaurs is so fast and why dinosaurs grow so big? To establish dinosaur embryology through these small bones from 195 million years ago.
Fig. 6 shows the research results at the National Synchrotron Radiation Research Center (NSRRC) in Taiwan, China, using Synchrotron Radiation FTIR Microscopy to scan the femur sections of these dinosaur embryos nearly 200 million years ago.Peaks of organic residues were found at the junction of bone and many "Primary Tubular Cavity". This spectrum is the earliest record of achievements. Subsequent analysis (Fig. 8) finally proved that these organic residues were the first collagen and its decomposition products, and some related papers have been published
[3,9,10]. These results, in addition to proposing that this is the oldest evidence of organic matter preserved in fossils, have completely overturned the wrong understanding that "organic matter cannot be preserved in fossils" and have a significant impact.
Fig. 7 shows the synchrotron radiation Micro-X-ray fluorescence (sr-Micro XRF) of the maxilla of Lufenglong embryo. The blue-green background of the image is phosphorus and calcium, representing apatite group minerals, and the red is organic sulfur, showing the two-dimensional distribution of organic sulfur in the maxilla. The source of organic sulfur should come from sulfur-containing amino acids after protein degradation, such as cysteine, cystine, methionine, etc. This is another evidence of preserved organic residue within the fossil.
To discuss the possible Preservation Mechanism of organic residues of Lufenglong and embryo fossils, from Fig. 4 and Fig. 6 to Fig. 8, in general, the three-dimensional chemical morphology is combined with two kinds of spectroscopy and element distribution.The relationship between organic residues and inorganic minerals in this fossil sample is very clear, and it can be confirmed that hematite, rather than goethite, plays a key role in preserving collagen. However, how does iron bind to organic matter so that collagen, which is easily degraded, can be preserved for so long? What is the underlying condensed matter chemistry mechanism? It remains to be further explored.
In addition, in the process of studying dinosaur embryology, interesting phenomena about rare earth elements in fossil bones have also been found.
The total concentration of 14 natural lanthanide rare earth elements in the bones of Lufenglong unearthed from Dawa Dinosaur Mountain in Lufeng and Yimenlong Chenglong found in Yimen is more than 20000 ppm, which is about 11 times that of the lanthanide rare earth elements in embryonic bones. The concentration of uranium in actinide rare earth elements is also five times higher. This phenomenon is the same in both dinosaurs and their embryos in Yunnan (Fig. 9)
[11,12]. Dinosaurs are late-maturing animals, and their young need to be fed for a period of time. Whether the combination of rare earth elements with apatite group minerals and the preservation of organic residues in dinosaur bone fossils are related to this is worth discussing.
4.2 The prevalence of organic residues preserved in solid fossils and the discussion of Carbonate Cementing preservation
"Fossil" literally means "change into stone." The organic parts of ancient organisms died and decayed into inanimate inorganic matter-stone. However, after using Fourier Transform Infrared Spectroscopy (FTIR), including synchrotron radiation sources, 63 different geological periods, sites and burial environments were examined, plus 15 living and 9 wall rock samples, each of which was scanned multiple times, a total of 107 spectra were selected from 525 scans. The results show that the preservation of organic residues in solid fossils is a common phenomenon, not a special case
[14]. Almost all organic compounds have alkyl groups (—CH
3,—CH
2) that show two or more well-defined peaks between 2800~3000 cm
-1, as shown in Figure 10; If a spectrum has these peaks, it is said that the sample contains alkyl functional groups, that is, organic matter, and alkyl groups can be used as indicators for confirmation screening. From the alkyl groups examined, it can be said that the preservation of organic residues in solid fossils is a common phenomenon, not a special case.
After obtaining the data, we propose two hypothetical mechanisms of organic matter preservation/non-preservation: "Saran Wrap" and "Carbonate Cementing" mechanisms. (1) It is possible that during the petrochemical process, the outermost protein or its degradation products undergo Repolymerizarion through some metal catalysts, forming a protective "fresh-keeping film" to protect the organic substances inside; (2) Another possibility is "carbonate gluing", in which carbonate encapsulates the organic matter and preserves the organic matter inside
[13].
There is a large group of fossils, such as shells and sea urchins, which are different from the bones dominated by apatite minerals and are fossils with carbonate matrix background. Within these fossils, there are also preserved organic residues. Fig. 11 shows the infrared spectra of three calcite (calcium carbonate); The upper is pure calcium carbonate synthesized in the laboratory, and the characteristic peaks are at 900 cm
-1 and 1440 cm
-1; The middle is a natural calcite crystal collected from Montana, USA. In addition to the two peaks characterized by pure calcite, there are other obvious peaks at 1800 cm
-1 and 2500 cm
-1, and a typical and clear alkyl peak at the alkyl characteristic, indicating that the calcite crystal produced in nature still preserves organic residues (represented by alkyl). The lower part is the calcite in the nacre. The alkyl group in the shell decreases with the heating temperature after 6 H, and the alkyl peak almost disappears at 600 ℃. The lower wavelength part (1900~600 cm
-1) also changes significantly, indicating that part of the organic matter has been burned
[14].
Fig. 12 a ~ J is a comparison of infrared spectra of mammal fossils from different sites, different burial environments, and different geological periods, from the Ediacaran body fossils about 565 million years ago, through the Paleozoic, Mesozoic, and Cenozoic, to the Mammalian fossils fished out of the Penghu Trench about 30,000 years ago
[15]; With the exception of fig. 12j, a well-defined alkyl peak can be seen within the alkyl wavelength; Comparing the mammal fossil Fig. 12i unearthed in Guanmiao, Tainan, Taiwan, China about 30,000 years ago with the mammal fossil Fig. 12j in the Penghu Trench, which was immersed in seawater for an unknown period of time, there is a very obvious difference in the alkyl peak between the two. The former fossil was produced in the continental facies.It has been preserved in the continental facies, so it is obvious that the organic residues represented by alkyl groups are preserved in it. In contrast, the animals that originally lived in the continental bridge were later soaked in the sea water with the rise of the sea level at the end of the glacial period, and the organic residues in them were washed out almost.
The most obvious example of carbonate gluing is shown in Figure 13. This is a two-dimensional infrared spectrum distribution of the serrules of the teeth of carnivorous dinosaurs. The upper three rows show the distribution of carbon dioxide physical adsorption (Physisorptions,2345 cm-1) and chemical adsorption (Chemisorption,1640 cm-1) of three carnivorous dinosaurs. The second row shows physical adsorption (2345 cm-1), and carbonate apatite A(Carbonatoapatite-A,879 cm-1) with carbonate apatite B(Carbonatoapatite-B,867 cm-1), respectively; The left side of the bottom row is the overlapping image of the three distribution maps in the fourth row, and the right side is the distribution map of alkyl groups. Comparing the distribution of carbon dioxide and the two carbonate apatites with the distribution of alkyl groups, it is clear that the cement layer formed by carbonate protects the organic residues in Dentine. On the bottom right is the distribution of alkyl groups (red), with a white line marking the rough boundary between organic residues and inorganics.
This phenomenon of carbonate bonding is most evident in dinosaur teeth with apatite group minerals as the matrix, and is also seen in fossil bones
[9][16]. Carbonate-based fossils have not been further explored, so whether the phenomenon of carbonate cementation is closely related to the preservation of organic residues remains to be further explored.
4.3 Metal Ions and Protein/Peptide/Amino Acid Compounds and Cells and Organelles
In recent years, through the study of Paleoproterozoic body fossils 2.2 billion years ago, paleochemical methods have been used to prove that these ancient organisms are the earliest "Multicellular + Eukaryote" in the history of life evolution on the earth:Eukaryotic domain, Liangshania peanuti Huang gen. et sp. nov. 2021) (Fig. 14), mass spectrometric analysis clearly shows Steranes, a fossilized degradation product of eukaryotic cell membranes
[17⇓⇓⇓⇓~22]; The cell membrane degradants of Prokaryote without nucleus, such as bacteria and archaea, are Hopanes without steranes
[23]. Mass spectrometry analysis showed a high proportion of steranes (Fig. 15, top), proving that these shrimps are eukaryotes
[24]; In the petroleum industry, the carbon number of steranes and hopanes is used to determine the original species of organisms that formed oil
[25]. The carbon number of steranes in these later organisms is more than C
28, and there are almost no steranes less than C
28[26⇓~28]. However, the carbon number of sterane in small shrimp has its own characteristics (Fig. 15B): in its body, short-chain C
20 accounts for the largest proportion (61%), plus C
22 and C
24 account for 70%.
Methylation and Demethylation of eukaryotic sterane side chains (at the C
17 position) were proposed in two papers, wondering if there is another possibility.The C
28 and the C
30 of the small shrimps are obtained by methanation from the side chain of the short-chain C
20~24,Or conversely, C
20~24 is the removal of side alkanes from C
28 and C
30[29,30]. It can be seen from Fig. 15 that the C
20~24 is only in the body of the small shrimp, and there is only a small amount of C
20 in the adjacent surrounding rock M1, and there is no C
22 and C
24 at all. However, M1/M2/M3 had high concentrations of C
28 and C
30, which were much higher than those in dried shrimps, with
M1C
28/
BodyC
28 and
M1C
30/
BodyC
30: of 2.64 and 4.03, respectively. Moreover, the concentrations of C
28 and C
30 in M2 and M3 were also relatively high, and the
M2C
28/
M3C
28 and
M2C
30/
M3C
30 were 1.56 and 0.021, respectively. Does this mean that there is alkylation from short chain to long chain or dealkylation from long chain to short chain between short chain and long chain?
It was confirmed to be a multicellular organism by multi-frequency microscopy, with an average cell size of 12.6 × 2.9 μm for shrimps and 20.5 × 5.2 μm for peanuts (Fig. 16)
[31,32]; Synchrotron Radiation Transmission X-Ray Microscopy (sr-TXM) with 30 nm resolution can be used to clearly observe many organelles in shrimp cells (Fig. 17). Such as Nucleus, Nuclear Envelope, Nucleolus, Nuclear Lamin, Golgi Apparatus, Heterochromatin and Endoplasmic Reticulum. This technique can see the cells and many organelles in fossils, which is different from the cells in fossils observed in other reports, usually only square or round images
[33].
In addition, 18 amino acids were found in these shrimps (fig. 18): Gly, Ala, Ser, Pro, Val, Thr, Cys, Ile, Asn, Asp, Gln, Glu, Met, His, Phe, Arg, Ty, Trp and Cys-Cys, with Ser and Asp being the most abundant. From the point of view of the preservation of organic residues in fossil bodies, excluding Biomarker compounds, this is the oldest record of the preservation of organic residues in solid fossils. Amino acids are basically water-soluble. These organisms have been in the sea for hundreds of millions of years after they died. Even after the strata rose to the land, there was a lot of water washing into the strata. How to preserve these amino acids
[34]. It is also suspected that these fossils may be the remains of bacterial colonies. However, different protein sources have different amino acid compositions. Through the Composition of amino acids that make up proteins, it can be inferred that the source proteins of the two are different
[35]. The most common amino acids (> 5%) in eukaryotes are Gly, Ser, Thr, Pro and Gln, which are higher than those in the wall rock in shrimps. The most common amino acids in prokaryotes are Arg, Ile, Ala, Glu, Lys, Asp, Leu and Val, which are higher in the wall rock than those in fossils
[36]. This rules out bacterial invasion into colonies and is another proof that the shrimp is a eukaryotic organism.
From the Raman spectra of shrimp and peanut (Fig. 19), they are almost the same, but there are some differences in intensity, so it can be said that the chemical composition should be the same. Is peanut the larva of shrimp. It is called Metamorphosis in the biological world. How to explain that the Raman spectra of the two are so identical?
Through XRF detection, it is found that there are four kinds of metals in these organisms: iron, titanium, manganese and barium (Fig. 20). Therefore, it is considered that the metal amino acids are combined in the body of the shrimp, which becomes a water-insoluble conjugate. Chelates of transition metals and amino acids, which have been used in the food industry, are insoluble above pH 7, while the pH of seawater is usually 7.2 or higher
[37,38][39]; This may explain why these amino acids are not washed out by water.
The Raman spectrum showed good results, with inorganic metal and organic peaks, as well as Ser-Ba
2+(1574 cm
-1) peaks in the Raman spectrum of peanuts
[40].
The metamorphic temperature of the formation can be calculated from the D and G bands of the Kerogen section of the Raman spectrum. The metamorphic temperature of the formation is about 221 ℃, which belongs to very low metamorphism
[41]. This can be used as a condition for the preservation of fossils. If the temperature of compressional metamorphism is very high, the organic material in the formation is burned out, and no solid fossils can be preserved.
Raman spectroscopy can also be used to perform three-dimensional scanning to produce the three-dimensional distribution of different Chemical components in fossils, which is called Chemical Morphology. The right side of Figure 21 shows the chemical Morphology of small shrimps 2.2 billion years ago. The length and width of the image are 60 μm. In the image, the cool color is the location of inorganic metal minerals, and the warm color is organic matter, including kerogen 1300~1650cm-1 alkyl. It can be seen that organic substances and inorganic substances are closely wrapped with each other, indicating that these metals and amino acids are closely combined. Fig. 21 is an image taken from the three-dimensional Raman video of shrimp and peanut.The yellow dotted line marks the outline of the cell. In terms of size, the cell size from the three-dimensional scanning of Raman spectra of shrimp and peanuts is consistent with that from multi-frequency microscopy and synchrotron radiation TXM, which is within a reasonable range. This is the third solid evidence of these two ancient biological cells.
An interesting phenomenon found in the course of this discussion is that the Raman spectra taken in situ at the same point in the two laboratories with different incident laser wavelengths have considerable changes in the positions and peak intensities of the D and G bands, as shown in Figure 22. The possible reason is that the chemical composition in these fossils,It shows the influence of "Electron-Phonon Coupling" in Condensed Matter Physics, which causes such a phenomenon. It has also been reported that the relationship between the Raman signal and the excitation laser wavelength cannot be explained by the principle of Non-Resonance Raman Scattering
[42]. The Raman signal decreases with the increase of the vibrational frequency. By resonance Raman scattering of these compounds, the electrons in the sample are excited to the excited State, and then the excited electrons return to the Ground State through several Relaxation Phases through some electron-phonon coupling in the excited state, as shown in fig. 23. The spectral results obtained in the relaxation phase of this excited state may be different from those of non-resonant Raman scattering.
Therefore, it is a reasonable inference that there are products of condensed matter chemistry in Daqing organisms. Nature used condensed matter chemical reactions more than 2 billion years ago, otherwise how could there be condensed matter physical phenomena? That is to say, there are condensed chemical products in peanut fossils! It proves that there were condensed chemical reactions in nature 2.2 billion years ago.
5 Discussion and Summary
5.1 Discussion
Effects of oxygen on eukaryotes. The increase of oxygen in the atmosphere has greatly changed the chemical environment of the earth's surface, leading to the emergence and survival of some organisms on the earth
[43,44]. During the Proterozoic Great Oxygenation Event (GOE) (blue box in Fig. 24) after Archean, the oxygen concentration in the atmosphere (2% -3%) increased by about ten times compared with that in Archean (0.2% -0.3%), and maintained for a long time. In the 200 million years before that, oxygen concentration fluctuated, especially during the period of 2.3-2.35 billion years. According to the evidence of carbon-13 drift (δ
13C Excursion), there were two high oxygen peaks in the Neoarchean, two small blue background parts on the left of Fig. 24. Many inorganic geochemical evidences show that there was also biological oxygen production in the 1 billion years before the Great Oxidation Event, and the early oxygen accumulation may be very dynamic. Chemical Photosynthesis of oxygen produces a large amount of oxygen. Many organisms on the earth, especially multicellular eukaryotes, need enough oxygen to appear, and the survival of these multicellular eukaryotes depends on the existence of a stable high concentration of oxygen. Therefore, after 2.22 billion years, it is theoretically possible that other multicellular eukaryotes will appear and exist. At present, only two multicellular eukaryotes of the Daqing Biota have been known for 2.2 billion years. Neoarchean fossils have been found in the fossil materials of central Yunnan, and the possibility of finding multicellular eukaryotes cannot be ruled out. Unlike central Yunnan, a series of ancient fossils appeared in other parts of the world during the long period of more than 2.2 billion years from Neoarchean to Neoproterozoic (28-540 million years).
Consideration of reaction solvent. These chemical reactions of organic preservation, not necessarily in a sufficient liquid water environment, are rapidly buried by terrestrial animals, possibly landslides and debris flows. Marine organisms are covered and buried after death before they begin to petrify, so they are not completely immersed in unlimited water. In both cases, chemical reactions, such as replacement of elemental ions in fossilization, come from a relatively limited amount of water in the adjacent formation. In addition, when fossils are pressed in thick sediments, the pressure of the stratum itself or the sea water above is very high, and the temperature of deep burial will be different from that of the surface. In addition, in the buried environment, which is usually anaerobic or hypoxic, there are also microorganisms, so the chemical reaction environment of the petrochemical process is whether the chemical reaction of hypoxia is condensed in such a small amount of water, high pressure and temperature. Once the fossil formation is uplifted or the surface is weathered to about 10 m, it will be affected by atmospheric oxygen and weather, and the chemical reaction conditions of the fossil will change. It is worth exploring what changes the chemical reaction conditions will have after the participation of oxygen.
The formation of silicified wood (commonly known as fossil wood) is a puzzling study. It is generally believed that the formation of wood fossils is usually due to the large amount of dust and silt brought by volcanic eruptions or crustal movements, or the sudden subsidence of marshes, which quickly buries the living plants, and silicate minerals replace organic matter, resulting in the wood fossils found so far. Another theory is that ancient plants were covered by sandstone for a long time, and the cell tissue was silicified by silicates to form hard wood fossils.
The above two mechanisms of wood fossil formation mention that the organic tissue in wood is replaced by "high concentration" of silicate during burial, thus preserving the original wood structure. However, the problem is that the water solubility of silicate is very low, even if the solubility of silicic acid in water is about 0.002 mol/L at 25 ℃, so how much water containing silicate needs to penetrate into the wood to replace it cell by cell? How long does it take to be replaced by silica from the core to the bark, how much high-concentration silicate-containing groundwater infiltration is required, what is the chemical mechanism of wood fossil formation, and how is it related to condensed matter chemistry? These problems are worthy of further study.
Amber is another important kind of fossil, which often contains ancient animals and plants, many of which are extinct species, providing valuable information about paleoecology and biological evolution. The paleontology preserved in amber should be the least variable of all fossils in terms of morphology and color. But from the point of view of chemical composition, these chemical reactions occur in viscous organic matter, almost no or very little water environment, what is the chemical reaction mechanism, what is the chemical change mechanism, and what role condensed matter chemistry plays here is still unknown.
5.2 Sum up
In a word, although we still don't know much about the role and mechanism of condensed matter chemistry in paleontology, from these examples of paleontological fossils,It can be seen that condensed matter chemistry is not only a bystander of theoretical chemistry, but also a key player. Its importance deserves our in-depth discussion to uncover the mystery of the bottom chemistry of countless chemical reactions from ancient organisms to fossils in our hands.
Declaration of Interest:The authors declare no competing interests。
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