9 The Last Big Bang Nationalism and the emergence of monolingualism are briefly described in Timothy Baycroft's Nationalism in Europe (1789-1945. - Cambridge University Press, 1998). The disappearance of world languages ​​is discussed in the book by David Nettle and Suzanne Romaine

5.2. Biological Explosion and Lack of Substance

The origin of arthropods - "arthropodization" (Vendian and Cambrian periods) In the "pre-molecular era" scientists had three scientific disciplines at their disposal, with the help of which it was possible to reconstruct the evolutionary history of organisms: 1. comparative anatomy, 2.

Cognitive Explosion The hypothesis of Machiavellian intelligence emerged in the late 1980s and has been steadily gaining ground ever since. In 2006, Sergey Gavrilets and Aaron Vause of the University of Tennessee at Knoxville developed a mathematical model that clearly demonstrates

10. Cultural explosion After the increase in the size of the brain opened up the possibilities for Homo sapiens to conquer the world, the human wave splashed out of Africa and, generation after generation, swept through the Old World, sweeping away everything in its path. Culture, at first imperceptible, then here, then

They arose on the border of the Cambrian almost suddenly, not being descendants of a pre-existing fauna.

However, other studies, both dating back to the 1970s and later, noted that complex animals similar to modern species arose long before the start of the Cambrian. In any case, numerous evidence in favor of the existence of life long before the Cambrian removed from the agenda the question of the "Cambrian explosion", as a phenomenon of the sudden emergence of life.

The question of the causes and mechanisms of the next increase in the complexity and diversity of life forms on the border of the Cambrian, which are not descendants of the disappeared Hainan and Vendian biota, remains open. To date, the problems of the "Cambrian explosion" are focused on two key issues:

• whether there really was an "explosive" increase in the diversity and complexity of organisms in the early Cambrian, and
• what could be the reason for such a rapid evolution.

Information sources

Building an accurate chronology of events at the boundary between the Precambrian and the Early Cambrian presents a significant difficulty. Because of this, the description of the sequence and interrelationship of certain phenomena in the framework of the discussion of the Cambrian explosion should be considered with some caution.

In addition to problems with dating, the study of events at the Cambrian boundary is hampered by the lack of paleontological material itself. Unfortunately, the further the period under study is from us, the less accessible its fossils are for studying. Among other things, the reasons for this are:

Remains of living organisms

Along with fossils, Cambrian deposits contain unusual high number deposits that have preserved imprints soft parts bodies of various organisms. Such prints allow us to study in detail animals that are not preserved as fossils, as well as the internal structure and functioning of organisms that are usually represented only by shells, spines, claws, etc.

In the Cambrian, the most important deposits are: Early Cambrian

Middle Cambrian

and Upper Cambrian deposit

• Orsten (Sweden).

Although all these deposits have excellently preserved the anatomical details of organisms, they are far from perfect. Most of the Cambrian fauna, perhaps, is not represented in them at all, since the deposits were formed in specific conditions (landslides or volcanic ash, which very quickly preserved the soft parts of the bodies). In addition, the known deposits cover only a limited period of the Cambrian and do not affect crucial time immediately before it starts. Since well-preserved burials are generally rare, and fossil deposits extremely rare, it is highly unlikely that they represent all types of organisms that have existed.

Fossilized footprints left by living organisms

Fossilized footprints consist mainly of paths and burrows left on seabed. Such tracks are extremely important because they provide the researcher with data on organisms whose bodies have not been preserved in fossils. Often, only they make it possible to study organisms belonging to a period from which the remains of animals capable of leaving such traces have not been preserved. Although it is generally not possible to accurately attribute tracks to the organisms that left them, tracks may provide the earliest evidence for the existence of relatively complex animals (like earthworms, for example).

Geochemical observations

In geological rocks belonging to the lower boundary of the Cambrian and its beginning, strong fluctuations in the isotopic composition of three elements are noted - strontium (87 Sr/ 86 Sr), sulfur (34 S/ 32 S) and carbon (13 C/ 12 C).

• mass extinction. Mass extinctions of organisms should directly increase the proportion of the 12 C isotope in sediments and thus reduce the 13 C/ 12 C ratio.
• Release of methane. In permafrost and on the continental shelf, bacteria-produced methane molecules are trapped in a "cage" of water molecules, forming a mixture called methane clathrate. Being produced by living organisms, this methane is enriched with the 12 C isotope. As the temperature rises or atmospheric pressure falls, the clathrates break down. This decay releases stored methane enriched in carbon-12 into the atmosphere. In the atmosphere, methane is converted to carbon dioxide and water, and the carbon dioxide reacts with minerals to form carbonaceous rocks with an excess of carbon-12. As a result, the isotopic composition of geological deposits shifts towards 12 C.

Comparative anatomy

Cladistics is a method of constructing an "evolutionary tree" of organisms, most often by comparing their anatomical structure. With the help of such an analysis, both modern and fossil organisms can be compared with each other in order to establish the course of their evolution. In a number of cases it can be concluded that group A must have appeared before the groups B and C, since they are more similar to each other than to A. By itself (without correlation with the data of paleontological excavations), this method does not say anything about the time when changes occurred, but it is able to restore the sequence of evolutionary development of organisms.

Molecular phylogenetics

Paleontological evidence

In this section, the main evidence is ordered by the time of formation of the deposits in which it was found, since dating is a central issue in the study of the Cambrian explosion. At the same time, one should keep in mind the ambiguity of the chronology of fossils belonging to this period.

The review of finds begins from a time long before the Cambrian and ends in the early Ordovician, since there is an opinion that the formation of the main types of modern fauna began before and ended after the Cambrian.

Molecular phylogenetic data (1.2 - 0.5 Ga)

There is still ongoing debate regarding the chronological interpretation of molecular phylogenetic data:

In any case, the data of molecular phylogenetics suggest that the formation of the main types of animals was a very long process, far beyond the 10 million years (about 543-533 million years ago) of the "Cambrian explosion".

Precambrian traces of metazoans

There is both indirect and direct paleontological evidence that multicellular organisms first arose long before the start of the Cambrian.

Decline of bacterial mats (1.25 Ga)

Precambrian stromatolite

modern stromatolites. Western Australia.

Stromatolites form an important part of the fossil record from about 3 billion years ago. Their heyday falls on a period of 1.25 billion years ago, after which they began to decline (both in total number and in diversity). By the beginning of the Cambrian, this reduction was already about 20%.

The most common explanation for the decline is the assumption that the microorganisms that make up the bacterial mats were preyed upon by other living organisms (which should indicate the existence of rather complex predators already about 1 billion years ago). This assumption is confirmed by the observed anticorrelations between the diversity and abundance of stromatolites - on the one hand, and the richness marine fauna- with another. Thus, the repeated decline of stromatolites occurred in the late Ordovician - immediately after another "outbreak" of the diversity and abundance of marine fauna. During the Ordovician-Silurian and Permian-Triassic extinctions, the recovery of stromatolites was again observed - with subsequent declines as the marine fauna recovered.

The development of means of protection among akritarchs. Early predation (1 Ga)

Acritarchs are fossilized fossils of an indeterminate nature, usually the shells of cysts of unicellular and multicellular algae. For the first time they are found in deposits dating back to 2 billion years ago.

About 1 billion years ago there was a sharp increase in their number, diversity, size, anatomical complexity and, especially, in the number and types of spines. The number of architarchs sharply decreased during the global glaciation, but subsequently recovered with the achievement of maximum diversity already in the Paleozoic.

Their exceptionally spiky forms, dating back to 1 billion years ago, may indicate the existence of predators already then, large enough to crush them or swallow them whole. Other groups of small Neoproterozoic organisms also have some form of defense against predators.

Traces left by multicellular organisms (1 billion years)

In India, sediments dated 1 billion years ago contain fossils that may be traces of organisms moving through and through soft rock. The traces found were apparently left directly under a layer of cyanobacterial mats that covered the seabed. The researchers concluded that the tracks owe their appearance to the peristalsis of three-layered multicellular organisms up to 5 mm in size - in other words, animals whose diameter was comparable to that of earthworms, and possibly had a coelom. Other researchers believe that these and similar finds older than 600 million years were left not by living organisms, but by physical processes.

Multicellular embryos from Doushanto (632-550 Ma)

However, the discovery in 2007 of embryos surrounded by a complex shell (in rocks aged 580-550 million years) indicates that the fossils in Doushanto are nothing more than resting eggs of multicellular invertebrates. Moreover, it became clear that some of the acritarchs found in the earlier rocks of Doushanto (632 Ma) actually represent shells of such embryos.

Another fossil from Doushantuo - Vernanimalcula(from 0.1 to 0.2 mm in diameter, age about 580 million years) - is considered by a number of scientists as the remains of a three-layer bilateral organism that had a whole, that is, an animal as complex as earthworms or molluscs. Despite doubts about organic nature these fossils, since all 10 specimens found Vernanimalcula are of the same size and configuration, it is unlikely that such uniformity is the result of inorganic processes.

The most recent Doushantuo deposits also show a sharp drop in the 13C/12C carbon isotope ratio. Although this change is worldwide, it does not coincide in time with other major events such as mass extinctions. Possible explanation consists in a "chain reaction" of the interconnected evolution of organisms and changes in the chemical composition of sea water. Multicellular organisms, actively absorbing carbon from water, could contribute to an increase in the concentration of oxygen dissolved in sea water, in turn, providing the emergence of new multicellular organisms (such as Namapoikia).

Ediacaran fauna (610-543 Ma)

spriggin

Multicellular fossils of the Ediacaran period were first discovered in the Ediacaran Hills in Australia, and then in deposits from other regions: Charnwood Forest (England) and the Avalon Peninsula (Canada). These fossils are 610-543 million years old (the Ediacaran period precedes the Cambrian). Most of them measured several centimeters and were significantly larger than their predecessors. Many of these organisms have no analogues with any of the species that lived before or after the Ediacaran period. It has been suggested that the most “strange” representatives of the Ediacaran fauna should be assigned to a separate kingdom - the “Vendozoa” (Vendozoa). It is among them that charnia is included - the most ancient of the finds of the Ediacaran period (age - 580 million years).

However, some Ediacaran organisms may turn out to be the precursors of later fauna:

Holes in sinks Cloudina. Selection in the "predator-prey" system

In some places up to 20% of fossils Cloudina contain holes with a diameter of 15 to 400 microns left by predators. Some Cloudina were damaged several times, which indicates their ability to survive attacks (predators do not re-attack empty shells). very similar to Cloudina fossils Sinotubulites found in the same burials do not contain holes at all. Such selectivity may indicate the existence already in the Ediacaran period of evolutionary selection of size classes, as well as specialization of prey in response to predation, which is considered as one of the causes of the Cambrian explosion.

Increasing diversity of traces left by organisms (565-543 Ma)

The earliest Ediacaran fossils, dating back to 610-600 million years ago, contained only traces left by cnidarians. About 565 million years ago, more complex traces appear. To leave them, the organisms required a skin-muscular pouch, and their general structure was to be more complex than that of cnidarians or flatworms.

Just before the beginning of the Cambrian (about 543 Ma), many new tracks appear, including upright burrows. Diplocraterion and Skolithos), as well as traces of possible arthropods ( Cruziana and Rusophycus). Upright burrows are evidence that worm-like animals have acquired new behaviors and possibly new physical abilities. Traces Cruziana and Rusophycus talk about the existence of an exoskeleton in the immediate predecessors of arthropods, although perhaps not as rigid as later.

Cambrian fossils

Shell fauna (543-533 Ma)

Fossils known as "small shelly fauna" (eng. small shelly fossils) have been found in different parts of the world and date back to the end of the Vendian (Nemakit–Daldynian Stage) and the first 10 Ma since the beginning of the Cambrian (Tommotian Stage). These include a very diverse collection of fossils: needles, sclerites (plates of armor), tubes, archaeocyates (a group of sponges or animals close to them), as well as small shells, very reminiscent of brachiopods and snail-like molluscs, although very small (1-2 mm in length).

Early Cambrian trilobites and echinoderms (530 Ma)

Fauna Sirius Passet (527 Ma)

The most common fossil of the Sirius Passet Greenland burial is arthropods. There are also a number of organisms with solid (mineralized) body parts: trilobites, chiolites, sponges, brachiopods. Echinoderms and mollusks are completely absent.

Sirius Passet's most bizarre organisms were Pambdelurion and Kerygmachela. Their long, soft-segmented bodies, with a pair of broad "fins" on most segments and a pair of segmented appendages at the back, make them similar to anomalocarids. At the same time, the outer parts of the upper surface of the "fins" had corrugated surfaces, which can be gills. Under each "fin" there is a short boneless leg. This structure allows you to associate them with arthropods.

Chengjiang fauna (525-520 Ma)

Haikouichthys - reconstruction

Anomalocaris - reconstruction

Hallucigenia - reconstruction

This fauna has been described from several fossil sites in Chengjiang County (Yuxi City, Yunnan Province, China). The most important is Maotianshan shale- a burial in which fossils of soft-bodied animals are very well represented. The Chengjiang fauna belongs to the period 525-520 million years ago - the middle of the early Cambrian, several million years later Sirius Passet and at least 10 Ma predates the Burgess Shale.

The body parts of the most ancient chordates (the type to which all vertebrates belong) were found in the fossils:

Representatives of groups close to arthropods were found in the same deposits:

These organisms probably belong to the group Lobopodia, to which of the modern groups the Onychophora belong.

About half of the Chengjiang fossils are arthropods, some of which had hard, mineralized exoskeletons, like most later marine arthropods. Only 3% of organisms had hard shells (mostly trilobites). Representatives of many other types of animals have also been found here:

• Priapulids (burrowing sea worms - ambush predators);
• Bristle-jawed (marine invertebrates that are part of plankton);
• Ctenophores (intestinal, outwardly similar to jellyfish);
• Echinoderms (starfish, sea cucumbers, etc.),
• Chiolites (mysterious animals that had small conical shells),

Early Cambrian crustaceans (520 Ma)

Burgess Shale (515 Ma)

Main article: Burgess Shale

Marrella

Pikaia - reconstruction

The Burgess Shale is the first known large burial site of the Cambrian period, discovered by Wolcott in 1909. The reanalysis of fossils by Whittington and his colleagues in the 1970s formed the basis of Gould's book " amazing life”, which opened the Cambrian explosion to the general public.

Among the Burgess fossil slates, arthropods are the most common, but many of them are unusual and difficult to classify:

Opabinia - reconstruction

Wiwaxia - reconstruction

In addition, samples of exotic organisms are presented in the burial:

Emergence of new ecosystems and types after the Cambrian

Due to a major extinction at the Cambrian-Ordovician boundary, typical Paleozoic marine ecosystems were formed only during the subsequent recovery of marine fauna. The earliest fossils related to bryozoans are also first discovered in the Ordovician period - well after the "Cambrian explosion".

findings

The long process of the emergence of multicellular

In Darwin's time, all that was known about fossils suggested that the main types of metazoans arose and formed within only a few million years - from the early to middle Cambrian. Until the 1980s, these ideas were still valid.

However, recent finds suggest that at least some three-layer bilateral organisms existed prior to the beginning of the Cambrian: Kimberella can be considered as early mollusks, and scratches on rocks near these fossils suggest a mollusk-like feeding method (555 million years ago). If we assume that Vernanimalcula had a three-layer bilateral coelom, this pushes back the emergence of complex animals by another 25-50 million years ago. Shell Hole Detection Cloudina also suggests the presence of advanced predators at the end of the Ediacaran period. In addition, some traces in fossils dating back to the mid-Ediacaran period (about 565 million years ago) could be left by animals that are more complex than flatworms and have a skin-muscular sac.

Long before this, the long decline of stromatolites (beginning about 1.25 billion years ago) speaks of the early appearance of animals difficult enough to "nibble" on. The increase in the abundance and diversity of spines in acritarchs at the same time leads to the conclusion that even then there were predators large enough for such protection to be necessary. At the other end of the time scale relating to the Cambrian Explosion, one should note the absence of a number of the main types of the current fauna up to the end of the Cambrian, and typical Paleozoic ecosystems - up to the Ordovician.

Thus, today the point of view is refuted, according to which animals of the "modern" level of complexity (comparable to living invertebrates) arose within only a few million years of the Early Cambrian. However, the vast majority of modern phyla first appeared in the Cambrian (with the exception of molluscs, echinoderms, and arthropods, possibly emerging in the Ediacaran period). In addition, an explosive increase in taxonomic diversity was also observed at the beginning of the Cambrian.

"Explosion" of taxonomic diversity in the early Cambrian

"Taxonomic diversity" means the number of organisms that differ significantly in their structure. At the same time, "morphological diversity" means the total number of species and does not say anything about the number of basic "designs" (many variations of a small number of basic types of anatomical structure are possible). There is no doubt that taxonomic diversity increased dramatically in the early Cambrian and remained at this level throughout the period - we can find modern-looking animals (such as crustaceans, echinoderms, and fish) at almost the same time, and often - and in common burials with organisms such as Anomalocaris and Halkieria, which are considered "uncles" or "great-uncles" of modern species.

Closer examination reveals another surprise - some modern-looking animals, such as early Cambrian crustaceans, trilobites and echinoderms, are in earlier deposits than some "uncles" or "great-uncles" of living groups that left no direct descendants. This may be the result of breaks and variations in the formation of fossil deposits, or it may mean that the ancestors of modern organisms evolved at different times and possibly at different rates.

Possible causes of the "explosion"

Despite the fact that rather complex three-layer animals existed before (and possibly long before) the Cambrian, evolutionary development in the early Cambrian seems to be extremely rapid. Many attempts have been made to explain the reasons for this "explosive" development.

Environmental changes

Increasing oxygen concentration

Earth's earliest atmosphere contained no free oxygen at all. The oxygen that modern animals breathe - both in the air and dissolved in water - is the product of billions of years of photosynthesis, mainly microorganisms (such as cyanobacteria). About 2.5 billion years ago, the concentration of oxygen in the atmosphere increased dramatically. Until that time, all the oxygen produced by microorganisms was completely spent on the oxidation of elements with a high affinity for oxygen, such as iron. Until they were completely bound on land and in the upper layers of the ocean, only local "oxygen oases" existed in the atmosphere.

Lack of oxygen could prevent the development of large complex organisms for a long time. The problem is that the amount of oxygen an animal can absorb from environment, is limited by the surface area (lungs and gills in the most complex animals; skin - in simpler ones). The amount of oxygen required for life is determined by the mass and volume of the organism, which, as the size increases, grow faster than the area. An increase in the concentration of oxygen in the air and in the water could weaken or completely eliminate this limitation.

It should be noted that a sufficient amount of oxygen for the existence of large vendobionts was already present in the Ediacaran period. However, a further increase in oxygen concentration (between the Ediacaran and Cambrian periods) could provide organisms with extra energy for the production of substances (such as collagen) necessary for the development of fundamentally more complex body structures, including those used for predation and defense against it.

Snowball Earth

There is abundant evidence that in the late Neoproterozoic (including the early Ediacaran period) the Earth was subjected to a global glaciation during which most of it was covered with ice, and the surface temperature was close to freezing even at the equator. Some researchers point out that this circumstance may be closely related to the Cambrian explosion, since the earliest known fossils date from a period shortly after the end of the last complete glaciation.

However, it is rather difficult to indicate a causal relationship of such catastrophes with the subsequent growth in the size and complexity of organisms. Maybe, low temperatures increased the concentration of oxygen in the ocean - its solubility in sea water almost doubles when the temperature drops from 30 ° C to 0 ° C.

Fluctuations in the isotopic composition of carbon

In deposits at the boundary of the Ediacaran and Cambrian periods, there is a very sharp decline, followed by unusually strong fluctuations in the ratio of carbon isotopes 13C/12C throughout the Early Cambrian.

Many scientists have assumed that the original fall is due to the mass extinction just before the start of the Cambrian. . It can also be assumed that the extinction itself was a consequence of the previous decay of methane clathrates. It is widely known that the emission of methane and the subsequent saturation of the atmosphere with carbon dioxide causes a global greenhouse effect, accompanied by various environmental disasters. A similar picture (a sharp drop in the 13 C/ 12 C ratio followed by fluctuations) was observed in the Triassic, when life was recovering from the mass Permian extinction.

However, it is rather difficult to explain how a mass extinction could cause a sharp increase in taxonomic and morphological diversity. Although mass extinctions, such as the Permian and Cretaceous-Paleogene, led to a subsequent increase in the number certain types from insignificant to “dominant”, however, in both cases, ecological niches were replaced, albeit by other, but equally complex organisms. At the same time, no abrupt growth of taxonomic or morphological diversity was observed in the new ecosystem.

A number of researchers assumed that each short-term decrease in the proportion of 13 C/ 12 C in the Early Cambrian represents a release of methane, which, due to the small greenhouse effect and an increase in temperature, led to an increase in morphological diversity. But even this hypothesis does not explain the sharp increase in taxonomic diversity at the beginning of the Cambrian.

Explanations based on the development of organisms

A number of theories are based on the idea that relatively small changes in the way animals develop from embryos to adults can lead to dramatic changes in body shape.

Emergence of the system of bilateral development

Hox genes various groups animals are so similar that, for example, you can transplant the human "eye formation" gene into a Drosophila embryo, which will lead to the formation of an eye - but it will be a Drosophila eye, thanks to the activation of the corresponding "working" genes. This shows that the presence of a similar set of Hox genes does not at all mean anatomical similarity of organisms (since the same Hox genes can control the formation of such different structures as human and insect eyes). Therefore, the emergence of such a system could lead to a sharp increase in diversity - both morphological and taxonomic.

Since the same Hox genes control the differentiation of all known bilateral organisms, the evolutionary lines of the latter must have diverged before any specialized organs could form. Thus, the "last common ancestor" of all bilateral organisms must have been small, anatomically simple, and most likely susceptible to complete decomposition not preserved in fossils. This circumstance makes its discovery extremely unlikely. However, a number of venodobionts (for example, kimberella, spriggin or Arkarua), may have had a bilateral body structure (according to a number of scientists, this is not so - the symmetry of venodobionts is not bilateral, but sliding, which fundamentally distinguishes them from most other organisms). Thus, such a development system could have arisen at least several tens of millions of years before the Cambrian explosion. In this case, some additional reasons are needed to explain it.

The development of sexual reproduction

Organisms that do not use sexual reproduction change very little. In most sexually reproducing organisms, the offspring receive about 50% of their genes from each parent. This means that even a small increase in the complexity of the genome can give rise to many variations in the structure and shape of the body. Much of the biological complexity probably arises from the action of relatively simple rules on a large number of cells functioning as cellular automata (an example of such an effect is the Conway game of Life, where complex shapes and complex behavior are demonstrated by cells acting solely on simple rules). The possible appearance of sexual reproduction or its significant development during the Cambrian explosion for very primitive and similar creatures may mean that there was the possibility of their interspecific and more distant interbreeding. This dramatically increased the variability. Only with the development of the genome do truly isolated species appear that do not interbreed with others. An example of modern creatures of this kind are corals.

development track

Some scientists suggest that as organisms become more complex, evolutionary changes general structure body superimposed secondary changes in the direction of better specialization of its existing parts. This reduces the likelihood of new classes of organisms passing through natural selection - due to competition with "improved" ancestors. As a result, as the general (at the level of the taxonomic class) structure is formed, a “development track” is formed, and the spatial structure of the body is “frozen”. Accordingly, the formation of new classes occurs "easier" in the early stages of the evolution of the main clades, and their further evolution takes place at lower taxonomic levels. Subsequently, the author of this idea pointed out that such a "freeze" is not the main explanation for the Cambrian explosion.

Fossils that could support this idea are ambiguous. It has been noted that variations in organisms of the same class are often greatest at the very first stages of clade development. For example, some Cambrian trilobites varied greatly in the number of thoracic segments, and subsequently this diversity has decreased significantly. However, samples of the Silurian trilobites were found to have the same high variability in structure as the Early Cambrian ones. The researchers hypothesized that overall decline diversity is associated with ecological or functional limitations. For example, one would expect less variation in the number of segments after trilobites (resembling modern woodlice) developed a convex body structure, which is an effective way to protect it.

Environmental explanations

Such explanations focus on the interaction between various types organisms. Some of these hypotheses deal with changes in food chains; others consider an arms race between predators and prey that may have caused the evolution of rigid body parts in the early Cambrian; a number of other hypotheses focus on more general mechanisms of coevolution (the most famous example is the coevolution of flowering plants with insect pollinators).

"Arms race" between predators and prey

By definition, predation presupposes the death of the prey, which makes it the strongest factor and accelerator of natural selection. The pressure on prey to better adapt must be stronger than on predators - because, unlike prey, they have a chance to make try again(This asymmetry is known as the "life versus lunch" principle - the predator only risks losing their lunch, while the prey risks their life).

However, there is evidence (for example, fossils of spiny acritarchs, as well as holes made in the shell of claudinids) that predation was present long before the beginning of the Cambrian. Therefore, it is unlikely that it in itself caused the Cambrian explosion, although it had a strong influence on the anatomical forms of the organisms that arose during this.

Appearance of phytophages

Stanley (1973) suggested that the appearance of protozoa (single-celled eukaryotes) 700 million years ago, "nibbling" microbial mats, greatly expanded food chains and should have led to an increase in the diversity of organisms. However, today it is known that "gnawing" arose more than 1 billion years ago, and the extinction of stromatolites began about 1.25 billion years ago - long before the "explosion".

Growth in size and diversity of plankton

Geochemical observations clearly show that the total mass of plankton became comparable to the current one already in the early Proterozoic. However, until the Cambrian, plankton did not make a significant contribution to the nutrition of deep-sea organisms, since their bodies were too small to quickly sink to the seabed. Microscopic plankton were eaten by other plankton or destroyed by chemical processes in the upper layers of the sea long before they penetrated into the deep layers, where they could become food for nekton and benthos (swimming organisms and inhabitants of the seabed, respectively).

In the composition of the early Cambrian fossils, mesozooplankton (medium-sized plankton, visible to the naked eye) was found, which could filter out microscopic plankton (mainly phytoplankton - planktonic "vegetation"). The new mesozooplankton may have been the source of the remains, as well as excreting excrement in the form of capsules large enough to submerge quickly - these may have been food for nekton and benthos, causing them to grow in size and diversity. If the organic particles reached the seabed, as a result of subsequent burial, they should have increased the concentration of oxygen in the water while reducing the concentration of free carbon. In other words, the appearance of mesozooplankton enriched the deep parts of the ocean with both food and oxygen, and thereby made possible appearance and the evolution of larger and more diverse inhabitants of the deep sea.

Finally, the emergence of phytophages among mesozooplankton could form an additional ecological niche for larger mesozooplankton predators, whose bodies, plunging into the sea, led to its further enrichment with food and oxygen. Perhaps the first predators among mesozooplankton were larvae of benthic animals, whose further evolution was the result of a general increase in predation in the seas of the Ediacaran period.

Many empty niches

James W. Valentine made the following assumptions in several papers: abrupt changes in body structure are "embarrassing"; change is much more likely to exist if it encounters little (or no) competition for the ecological niche it targets. The latter is necessary so that the new type of organisms has enough time to adapt to its new role.

This circumstance should lead to the fact that the implementation of major evolutionary changes is much more likely at the initial stages of ecosystem formation, due to the fact that subsequent diversification fills almost all ecological niches. In the future, although new types of organisms continue to emerge, the lack of empty niches prevents their spread in the ecosystem.

Valentine's model explains well the uniqueness of the Cambrian explosion - why it happened only once and why its duration was limited.

Notes

1. Darwin, C. On the Origin of Species by Natural Selection. - London, United Kingdom: Murray, 1859. - P. 315–316.
2. Walcott, C.D. Cambrian Geology and Paleontology // Smithsonian Miscellaneous Collections. - 1914. - T. 57. - P. 14.
3. Whittington, H. B.; Geological Survey of Canada. Origins and early evolution of predation // The Burgess Shale. - Yale University Press, 1985.
4. Gould, S.J. Wonderful Life: The Burgess Shale and the Nature of History. - New York: W.W. Norton & Company, 1989. - ISBN 0-393-02705-8
5. McNamara, K.J. Dating the Origin of Animals // Science. - 1996-12-20. - T. 274. - No. 5295. - S. 1993–1997.
6. Awramik, S.M. Precambrian columnar stromatolite diversity: Reflection of metazoan appearance // Science. - 1971-11-19. - T. 174. - No. 4011. - S. 825–827.
7. Fedonkin, M. A.; Wagoner, B. The late Precambrian fossil Kimberella is a mollusc-like bilaterian organism // Nature. - 1997. - T. 388. - S. 868–871.
8. Eskov, K. Drafts of the Lord God // Knowledge is power. - 2001. - № 6.
9. Jago, J. B., Haines, P. W. Recent radiometric dating of some Cambrian rocks in southern Australia: relevance to the Cambrian time scale // Revista Española de Paleontologia. - 1998. - S. 115–22.
10. Eskov K. Yu. Amazing Paleontology: A History of the Earth and Life on It. - M .: Publishing house of NTs ENAS, 2007. - 540 p. - (What the textbooks were silent about). - ISBN 978-5-93196-711-0
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In the same book “The Origin of Species”, Charles Darwin wrote: “If numerous species belonging to the same class began to exist simultaneously, then this will be a death blow to the theory that provides for evolution from a common ancestor by natural selection.

Modern scientists, having studied in detail the fossil remains, are convinced that living beings appeared on Earth suddenly. In the so-called Cambrian layer, the remains of trilobites, sponges, worms, starfish, snails, floating crustaceans, cephalopods, arthropods, etc. were found. Unicellular and bacteria were also found here and a little lower. The presence of any multicellular organisms earlier than the Cambrian is a controversial point. Thus it is evident that many species, distinct from each other, and already having perfect organisms, existed at the same time and have no ancestors from which they could have descended. In geology, this phenomenon is called the Cambrian Explosion.

Rice. Inhabitants of the Cambrian period

By the way, it is also difficult for evolutionists to unambiguously answer the question why in modern nature, as well as in the nature of the Cambrian period (which was supposedly more than 500 million years ago), there are sponges, worms, starfish, snails, floating crustaceans, etc.? Why are they for this a long period did not evolve into higher forms? If evolution is a positive, inevitable upward movement of all living things, then why hasn't it touched all beings? It would be more logical if at present only one crown of evolution remained on the planet - man!

Why do amoebas, insects, fish, amphibians, reptiles, mammals, monkeys and humans still live on Earth at the same time? Perhaps for the same reason that the coelacanth fish still exists: it lived a long time ago, continues to live today. Even if you try to believe in evolution, you will have to answer the question: has evolution stopped today or not? However, answering this question raises other questions that remain unanswered.

If we assume that all living creatures, from simple to complex, are still in the process of evolution, then we will immediately have to explain why there are no living transitional forms among them. If we imagine that evolution has ended and the creatures that have reached perfection stopped their development a long time ago, and the rest are exterminated through natural selection, then inexplicable fact why there are not enough dead intermediate links in evolution. But the remains of transitional forms should be in the trillions and even sextillions, being accumulated in the bowels of the earth supposedly for millions of years.

For ease of study, the history of our planet and life on it was divided into periods of time, the boundaries of which are geological changes in the earth's crust - the processes of mountain building, the rise and fall of land, changes in the shape of continents, global climate change.

The longest chronological periods in the history of the Earth are called eras (they lasted hundreds of millions of years). Eras are further subdivided into periods.

Scientists get all the information about the past of the Earth by examining the geological evidence of the world chronicle. The bowels of the planet consist of various layers of rocky and sedimentary rocks, which were formed under the continuous influence of external conditions that determined the appearance of the Earth in the distant past. Geological formations have preserved and carried through millions of years information about living organisms that inhabited the oceans and land in different geological periods. Thanks to this, today we have the opportunity to imagine the appearance of the Earth of the distant past and trace the evolution of life over 3.5 billion years from the moment of its appearance.

Researching ancient rocks and fossils, scientists have discovered two unexplained phenomena in the geological and biological past of the Earth. The first phenomenon is called World Disagreement, and is a contact rocks from different geological periods not following one after the other. Such contact violates the logical sequence of the layers, according to the chronological periodicals of various historical stages in geology. It should be noted that illogical contact of rocks is found everywhere. This is due to the mixing of the structures of the earth's crust as a result of tectonic activity and erosion processes. However, the Global Unconformity cannot be explained by this, as it is ubiquitous and reflects an uncoordinated contact between rocks approximately 2.9 billion years old and young Cambrian deposits that formed approximately 500 million years ago.

The second phenomenon concerning the biological past of the Earth is called the "Cambrian Explosion". Paleontologists gave this term to the sudden rapid increase in the species diversity of living organisms in the Cambrian period (at the very beginning of the Paleozoic era). It happened for chronological period at 30 million years (approximately 542–510 million years ago). For such an insignificant period of time by paleontological standards, the number species increased hundreds of times. Suddenly, a great variety of varieties of shell organisms appeared, the first chordates and prothoracids (the so-called trilobites) arose.

The most famous and studied proof of the existence of these two scientific phenomena located in the USA. This is grand canyon lying on the Colorado Plateau, Arizona. A favorite place for tourists from all over the world. It was there that paleontologists have found the largest number of fossilized life forms, so unlike the soft-bodied organisms that lived in the pre-Cambrian Ediacaran period.

For a long time, scientists from all over the world have been looking for a clue to the phenomena of the Cambrian period. Recently, a theory has emerged in scientific circles that explains the nature of the emergence of the Global Discord and the "Cambrian Explosion" and establishes the relationship between these two unique facts of planetary history.

About 600 million years ago, great changes began to occur in the depths of the Earth, causing tremendous shifts on the surface of the planet. There's been a movement lithospheric plates, which tore apart the once single continent - Gondwana, many volcanoes simultaneously erupted waves of lava. Widespread earthquakes generated huge tsunamis. The surface of the land was several times subjected to flooding by the waters of the oceans, which was the main reason for the formation of the World Discord.

Younger and located superficially sedimentary layers are destroyed by water and related factors several times slower than older and deeper rocks. It was during the periods of flooding of the continents that erosion and degradation of sedimentary rocks occurred, the exposure of ancient rocks, which were subjected to rapid erosion. The products of the destruction of rocks dissolved in billions of tons in the waters of prehistoric oceans. The concentration of potassium, calcium, magnesium, iron, phosphate, sulfate ions suddenly increased. The acid-base balance of the world's oceans has shifted sharply to the alkaline side.

The main principle of life says that in order to exist, a living organism must constantly maintain the constancy of the internal environment. The primitive soft-bodied descendants of modern organisms had to evolve rapidly to withstand drastic change living conditions. The momentary leap in the evolution of ancient life was a forced response to a sudden increase in the concentration of various salts in sea water. The result of this evolutionary leap was the mechanisms of mineralization, which directed the evolution of ancient animals in a different way.

This theory is supported by the simultaneous appearance of a mineral skeleton in unrelated organisms during the Cambrian period. The main three varieties of mineral salts determined the direction of the further evolution of life - these are calcium phosphate, the mineral basis of the chordate skeleton, calcium carbonate and silicon oxide, which are the material of the shells of the first shell creatures. Calcium, silicon and phosphates are the main components of the Cambrian formations that formed the areas of the World unconformity.

The newly emerged young life forms had an advantage over the primitive soft-bodied, devoid of hard organs. The new organisms had teeth for attack and defense, shells for defense, chords, and hard skeletons that allowed them to move purposefully and at higher speeds through the water. The suddenly acquired mechanisms of mineralization allowed the young creatures to multiply in unprecedented numbers and supplant the old forms of life. The mass of the very first creatures with mineral organs was the basis for the formation of geological layers of the Cambrian period, which formed on the ancient layers of rocks.

Forms of life with mineral skeletons began to form as early as the Precambrian, but it was the geological anomalies that formed the World Unconformity that accelerated this process many times and gave it an explosive character. The trigger of the processes that created the appearance of the bulk of modern animal species was the rapid mineralization of the world's oceans. Geological processes determined biological evolution for millions of years to come.

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02.12.2016

Hello everyone again! In this post I will try to talk about a unique event in the history of life on Earth. We will talk about the Cambrian explosion, or as it is also called, the Cambrian radiation. The Cambrian explosion is the brightest event in the paleontological record of the planet, when in a relatively short period of time (several tens of millions of years) there is a sharp increase in the number of fossil remains of living beings and, at first glance, as if from nowhere, almost all modern types of animals appear (chordates, arthropods , mollusks, echinoderms, etc.).

It had predecessors, but Cloud managed to capture the idea of ​​the Cambrian explosion with the greatest eloquence and geological sophistication. In addition to his great leadership and mentoring of a generation of paleontologists, he developed an integrative approach to paleontology, adding skills in paleogeography, carbonate stratigraphy, and carbonate sedimentology. His later career in University of California, Santa Barbara, expanded his interests to astrobiology and the origin of life. His observations as a paleontologist led him to characterize the Phanerozoic fossil record as a series of evolutionary eruptions, with the Cambrian being the largest of all.