290 million years ago, beginning of the Permian. The creature that jumps out of the water is an eriops, an advanced two-meter amphibian, a relic of a previous era - the Carboniferous period.
How did prehistoric animals live in the Triassic period - the time when nature first began to think about creating a mammal? The author publishes paintings by Canadian artist Julius Chotogni and tells how the world looked more than 200 million years ago.
Want more pictures of Julius Ciotonyi with explanations?
290 million years ago, beginning of the Permian. The creature that jumps out of the water is an eriops, an advanced two-meter amphibian, a relic of a previous era - the Carboniferous period. Remember how the first tetrapods arose - neither fish nor meat? It was even earlier, in the Devonian, 360 million years ago. And so it turns out, for almost 70 million years - more than the time has passed from the extinction of the dinosaurs to the present day - these very tetrapods continued to sit in the swamp. They had nowhere and no reason to get out in particular - the land surface, free from glaciers (and the Carboniferous period was a rather cool era), was either swamps littered with rotting tree trunks, or a continental desert. In the swamps, the creatures swarm. In fact, they did not waste time in vain and changed little only in appearance - anatomically, the most advanced of them managed to go from almost a fish through a "classic" amphibian to almost a reptile - that's how this eriops belongs to the class of temnospondyls.
By the beginning of the Permian period, the most primitive of the temnospondyls still retained fish features - a lateral line, scales (and in some places, for example, on the belly), but these were not openwork creatures like modern newts and frogs - no, they were powerful, like crocodiles, with skulls resembling towers tanks: solid, streamlined, only with loopholes for the nostrils and eyes - these were these amphibians. Previously, they were called "stegocephals" - shell-headed ..
The largest is a sclerocephalic, judging by the rounded mouth, it is young (in old individuals that grew up to two meters in length, the muzzle was elongated and resembled the muzzle of an alligator, and the tail, on the contrary, was shortened - perhaps with age, sclerocephals became more “ground-based” and resembled way of life of crocodiles, this is how their remains are distributed - young in the sediments of deep lakes, skeletons of old ones in the former shallow waters and in swamps). A sclerocephalic is chasing an acanthode fish, and in the background is an ortacanth - a freshwater shark, also young (an adult would reach a length of three meters and would chase the sclerocephalic itself). On the right, lying at the bottom near the shore - even more than eriops, an advanced creature - seymuria: no longer an amphibian, not yet a lizard. She already had dry skin and could stay out of the water for a long time, but she still spawned, and her larvae had external gills. If she laid eggs, she could already be called a reptile. But Seymuria is stuck in the past - eggs were invented by some of its relatives at the end of the Carboniferous, and these relatives laid the foundation for the ancestors of mammals and reptiles.
All these creatures in the pictures are not ancestors to each other - these are all side branches of the evolutionary chain that ultimately led to the appearance of mammals, and only illustrate its stages. Evolution is usually done by small non-specialized critters, but it is not interesting to show critters - at that time they all looked like lizards ... their mighty relatives, albeit dead-end branches, are another matter:
On the left is Ophiacodon, on the right is Edaphosaurus. One with a sail, the other without, but both of these creatures belong to the same order of pelycosaurs and are evolutionarily closer not to dinosaurs, but to mammals - more precisely, this group got stuck somewhere in the third of the way from amphibians to mammals and remained so until they not supplanted by more progressive relatives. The sail on the back is one of the first attempts of synapsids not to wait for favors from nature, but to learn to regulate their body temperature on their own; our ancestors and their relatives, in contrast to other lizards, having barely stepped onto land, for some reason immediately began to be interested in this topic.
Theoretical calculations (we don’t have experimental pelycosaurs anyway) show that a 200-kilogram cold-blooded dimetrodon (and in the figure it is also a pelycosaurus, but predatory and from a different family) would warm up without a sail from 26 ° C to 32 ° C in 205 minutes, and with a sail - in 80 minutes. Moreover, due to the vertical position of the sail, he could use the earliest hours of the morning, while the unsailed had not yet come to their senses, and quickly move on to outrages:
For breakfast, God sent Xenacanthus, another freshwater shark, to the Dimetrodons. More precisely, those that are closer are dimetrodons, and further away their smaller brother secodontosaurus drooped - more frail and with a muzzle resembling a crocodile. On the left, an eriops silently drags a diplocaulus in its mouth - a strange amphibian with a head like a hammerhead shark; sometimes they write that such a head is a protection against swallowing by larger predators, another theory suggests using it as a kind of wing for swimming ... but I just wrote about the hammerhead shark and thought: maybe it, like the hammerhead shark, was electric detector to search for small organisms in the mud? Behind them is an edaphosaurus, and from above, on a branch, you can, looking closely, see an areoscelis - a creature resembling a lizard - one of the first diapsids. That's how it was then - the relatives of the ancestors of mammals tore meat, and the tiny insectivorous relatives of the ancestors of dinosaurs looked at them with mute horror from the branches.
As a result, the sail turned out to be an unsuccessful design (imagine carrying such a radiator yourself - it was not foldable!). In any case, sailing pelycosaurs basically died out by the middle of the Permian, supplanted by the descendants of their sailless relatives ... but the fact remains that therapsid animal lizards, of which we are descendants, descended from sphenacodonts - a group of pelycosaurs, to which the ugly Dimetrodon belonged (only not from dimetrodon, of course, but from some of its small relatives). Some kind of successful alternative was found to the sail - perhaps even such creatures already had primitive metabolic warm-bloodedness:
On the left - titanosuchus, on the right - moschops. This is already the middle of the Permian, about 270 million years ago, South Africa. More precisely, today their bones ended up in South Africa, and then they lived on the same mainland with a decorated carenite. If pelycosaurs have gone a third of the way from amphibian to mammal, then these monsters are two-thirds. Both of them belong to the same order of tapinocephals. Very massive - however, this is typical for all tetrapods of that time, the skeletons of creatures the size of a dog or horse have proportions like those of an elephant - thick bones with swollen condyles, a solid, like in stegocephalic ancestors, a skull with three eye sockets ... I don’t know, with what it is connected with, hardly with any external conditions(arthropods of that time have approximately modern proportions), rather, with imperfection of bone tissue - less strength was compensated by greater thickness. Both animals in the picture reached two meters in length and moved like a cross between a rhinoceros and a Komodo monitor lizard, including a predatory (or omnivorous) titanosuchus. They could not chew food for a long time - they did not have a secondary palate that allows them to eat and breathe at the same time. They didn’t really know how to bend down, especially Moschops, and he didn’t need to - there was no grass yet, he ate leaves and half-rotten trunks, and grazed, perhaps lying down - you won’t stand for a long time - or in the water.
The climate in the Permian period was characterized, on the one hand, by increasing aridity, on the other hand, by the appearance and spread of plants capable of growing not only knee-deep in water - gymnosperms and true ferns. Following the plants, animals also moved to dry land, adapting to a truly land-based way of life.
This is already the end of the Permian period, 252 million years ago. Horned red-blue creatures in the foreground are wonderful elginia, small (up to 1 m) pareiasaurs from Scotland. Their coloration, perhaps, the artist hints that they could be poisonous - it is known that the skin of pareiasaurs contained a large number of glands. This other branch of the path from amphibians to reptiles, independent of synapsids, apparently remained semi-aquatic and also became extinct. And here are the plump ones in the background - Gordonia and two Geikia - dicynodonts, creatures completely independent of water with dry skin, a secondary palate that allowed chewing food and two fangs for (probably) digging. Instead of front teeth, they had a horny beak, as later in ceratopsids, and their main diet may have been the same. Like ceratopsians at the end of the Mesozoic, dicynodonts at the end of the Paleozoic were many, different and everywhere, some even survived the Permian-Triassic extinction. But who is sneaking up on them is not exactly clear, but it seems to be some small (or just young) gorgonopsid. There were also large ones.
These are two dynogorgons discussing over the body of some non-small dicynodont. Dinogorgons themselves are three meters high. These are one of the largest representatives of Gorgonopsians - already almost animals, less progressive than dicynodonts (for example, they did not acquire a secondary palate and diaphragm, they did not have time), while standing closer to them to the ancestors of mammals. Very agile, strong and dumb creatures for those times, apex predators of most ecosystems ... but not everywhere ..
In the foreground are dicynodonts again, and further to the right is an archosaurus, a three-meter crocodile-like creature: not yet a dinosaur, but one of the lateral branches of the ancestors of dinosaurs and crocodiles. He has about the same relation to dinosaurs and birds as dynogorgons have to us. Long fish - saurichthys, distant relatives of sturgeons, who played the role of pikes in this ecosystem. To the right underwater is Chroniosuchus, one of the last reptiliomorphs with which we started this story. Their time is up, and for the rest of the creatures depicted in the picture, the world will soon change ...
The question of how old the human race is: seven thousand, two hundred thousand, two million or a billion is still open. There are several versions. Let's consider the main ones.
Young "homo sapiens" (200-340 thousand years)
If we talk about the species of homo sapiens, that is, "reasonable man", he is relatively young. Official science gives him about 200 thousand years. This conclusion was made on the basis of a study of mitochondrial DNA and the famous skulls from Ethiopia. The latter were found in 1997 during excavations near the Ethiopian village of Kherto. These were the remains of a man and a child, whose age was at least 160,000 years old. To date, these are the most ancient representatives of Homo sapiens known to us. Scholars dubbed them homo sapiens idaltu, or "oldest sane man."
At about the same time, maybe a little earlier (200 thousand years ago), the progenitor of all modern people, “mitrochondria Eve”, lived in the same place in Africa. Her mitochondria (a set of genes that is transmitted only through the female line) is present in every living person. However, this does not mean that she was the first woman on earth. Just in the course of evolution, it was her descendants who were most fortunate. By the way, “Adam”, whose Y-chromosome every man has today, is relatively younger than “Eve”. It is believed that he lived about 140 thousand years ago.
However, all these data are inaccurate and inconclusive. Science is based only on what it has, and more ancient representatives of homo sapiens have not yet been found. But the age of Adam has recently been revised, which can add another 140 thousand years to the age of mankind. A recent study of the genes of one African American, Albert Perry, and 11 other villagers in Cameroon showed that they have a more “ancient” Y chromosome, which was once passed on to his descendants by a man who lived about 340,000 years ago.
"Homo" - 2.5 million years
Homo sapiens is a young species, but the genus Homo itself, from which it comes, is much older. Not to mention their predecessors, the Australopithecus, who were the first to stand on both legs and start using fire. But if the latter still had too many features in common with monkeys, then the oldest representatives of the genus “Homo” - homo habilis (handy man) already looked like people.
Its representative, or rather its skull, was found in 1960 in the Olduvai Gorge in Tanzania, along with the bones of a saber-toothed tiger. Perhaps he fell prey to a predator. Then it was already established that the remains belonged to a teenager who lived about 2.5 million years ago. Its brain was more massive than that of typical Australopithecus, the pelvis allowed easy movement on two legs, and the legs themselves were only suitable for upright walking.
Subsequently, the sensational find was supplemented by an equally sensational discovery - homo habilis himself made tools for labor and hunting, carefully selecting materials for them, following them for long distances from the sites. This was found out due to the fact that all his weapons were made of quartz, which was not near the places of residence of the first person. It was homo habilis who created the first - the Olduvai archaeological culture, from which the era of the Paleolithic or Stone Age begins.
Scientific creationism (from 7500 years ago)
As you know, the theory of evolution is not considered fully proven. Its main competitor was and remains creationism, according to which both all life on Earth and the world as a whole were created by the Higher Mind, the Creator or God. There is also scientific creationism, whose followers point to scientific confirmation of what is said in the Book of Genesis. They reject the long chain of evolution, arguing that there were no transitional links, all living forms on earth were created complete. And they lived together for a long time: people, dinosaurs, mammals. Until the flood, traces of which, according to them, we still meet today - this is a large canyon in America, dinosaur bones and other fossils.
Creationists do not have a single opinion on the age of mankind and the world, although they all in this matter are guided by the first three chapters of the first Book of Genesis. So-called "young earth creationism" takes them literally, insisting that the entire world was created by God in 6 days, about 7,500 years ago. Followers of "old-earth creationism" believe that God's work cannot be measured by human standards. Under one "day" of creation may be meant not a day at all, millions and even billions of years. Thus, the true age of the earth and humanity in particular is almost impossible to determine. Relatively speaking, this is a period from 4.6 billion years (when, according to the scientific version, the planet earth was born) to 7500 years ago.
MOSCOW, June 7 - RIA Novosti. Paleontologists have discovered in Morocco today the oldest remains of modern humans, Homo sapiens, whose age is at least 300 thousand years old and suggests that people appeared much earlier than was commonly believed, according to an article published in the journal Nature.
"These ancient hominids, especially one of the women, if dressed in modern clothes, combed and released into the crowd of modern people, would absolutely not stand out against their background. They would look completely normal in the eyes of the townsfolk, and would stand out from the crowd only with an unusually elongated skull and "stocky" body, visible to professional anthropologists," says Jean-Jacques Hublin of the Institute for Evolutionary Anthropology in Leipzig, Germany.
Dark Ages of Humanity
Until recently, anthropologists and paleontologists believed that modern man, Homo sapiens, originated in East Africa about 200 thousand years ago, several hundred thousand years after the separation of the ancestors of Neanderthals and Cro-Magnons. The first people, as shown by excavations, penetrated into the Middle East about 70 thousand years ago, and into Europe - about 45 thousand years ago.
Scientists: Neanderthals interbred with humans already 100 thousand years agoScientists have found inclusions of the human genome in the oldest samples of Neanderthal DNA from the Altai, which tell us that the first people entered Asia already 100 thousand years ago, long before the migration of the Cro-Magnons to Europe.On the other hand, finds recent years and genetic studies suggest that people could have left Africa much earlier, at least 130,000 years ago, and contacted Neanderthals for a long time. Moreover, South Africa also claims to be the ancestral home of mankind today, in the caves of which scientists recently found Cro-Magnon tools aged 150 thousand years and the remains of Homo naledi, potential human ancestors who lived in the Naledi cave about 330 thousand years ago.
Ublin and his colleagues say that in fact neither region can claim to be the "ancestral home" of mankind, based on the finds they made at Jebel Iroud in northwestern Morocco.
The first excavations, according to Ublin, began here back in the 1960s, when local miners working on pyrite deposits accidentally stumbled upon a layer of sedimentary rocks in which they found a skull and other human remains, stone tools dating back to the Middle Paleolithic, and many bones of gazelles, wildebeest and other animals.
The skulls and bones of the people found in this mine were very similar to the remains of modern Homo sapiens and Neanderthals, which is why the chief geologist of the mine and scientists from the University of Rabat, to whom he gave this remains, did not give them special attention. They considered that these Cro-Magnons or Neanderthals were buried in the soil quite recently, about 40 thousand years ago, in the era of the colonization of the Earth by the first tribes of people.
Ublin says his team began excavating at Jebel Irud in 2004, trying to find new human remains, classify them and calculate their age. In total, scientists were able to find 22 fragments of human skulls and bones belonging to five different individuals - one man, two children and two women.
Paleontological pan-Africanism
The shape of the bones and especially the skull, as the scientist recalls, immediately indicated that they were dealing with ancient Homo sapiens, and not Neanderthals or the alleged common ancestors of man and the first "natives of Europe." The inhabitants of Jebel Irud generally resembled modern humans, except that they had a heavier build, a slightly elongated skull, and a less developed brain.
This discovery led paleontologists to seek the help of physicists, who helped them accurately measure the dates of burial of skulls and bones from the isotope fractions of uranium and other heavy elements contained inside tools burned in the hearths of the inhabitants of Jebel Irud.
When Ublin and his colleagues saw these dates, they realized that they were actually dealing with potentially the oldest remains of modern humans on Earth - their age exceeded 300,000 years, which is 100,000 years older than the oldest remains of people from Ethiopia.
This discovery, as the paleontologist notes, completely overturns our ideas about the evolution of mankind. It turns out that modern people spread and existed in three different parts of Africa already 300 thousand years ago. This, accordingly, suggests that the species Homo sapiens arose much earlier than previously thought - at least several tens of thousands of years before the mark of 300 thousand years and not earlier than 650 thousand years ago, when the ancestors of Neanderthals and humans separated.
"People often don't realize that there are two completely different questions - the origin of our species, Homo sapiens, and the emergence of modern humans who look exactly like us. Our discovery only addresses the first question, and we are only talking about the fact that people began to spread across Africa earlier than 300 thousand years ago. It is possible that some kind of "cradle of mankind" existed, but we still have no hints of where it could be - in the south, in the east, and maybe in the north of Africa, " the scientist explained in an interview with RIA Novosti.
According to Ublin, the problem may actually be even wider - it is quite possible that the metaphorical "Gardens of Eden" where the first people appeared did not exist, and that modern people are the product of the "co-evolution" of several populations of members of the genus Homo. They could contact each other and live in different parts of Africa, periodically falling into isolation due to the formation and disappearance of deserts.
"We assume that early humans existed in all regions of Africa and gradually evolved towards the growth and complexity of their brains, periodically exchanging genes during periods favorable climate. And so we believe, and in the past I was of the opposite opinion, that there were no solitary "gardens of Eden". If they were, then they should be called the whole of Africa as a whole," Ublin concludes.
One of the curves showing sea level fluctuations over the past 18,000 years (the so-called eustatic curve). In the 12th millennium BC. sea level was about 65 m below the present, and in the 8th millennium BC. - already at incomplete 40 m. The rise in level occurred quickly, but unevenly. (According to N. Mörner, 1969)
The sharp drop in ocean level was associated with the widespread development of continental glaciation, when huge masses of water were withdrawn from the ocean and concentrated in the form of ice in the high latitudes of the planet. From here, the glaciers slowly spread towards the middle latitudes in the northern hemisphere by land, in the southern hemisphere - by sea in the form of ice fields that overlapped the shelf of Antarctica.
It is known that in the Pleistocene, the duration of which is estimated at 1 million years, three phases of glaciation are distinguished, called in Europe the Mindelian, Rissian and Würmian. Each of them lasted from 40-50 thousand to 100-200 thousand years. They were separated by interglacial epochs, when the climate on Earth warmed noticeably, approaching the modern one. In some episodes, it even became 2-3° warmer, which led to the rapid melting of ice and the release of huge spaces on land and in the ocean from them. Such dramatic climate changes were accompanied by equally sharp fluctuations in ocean levels. During the epochs of maximum glaciation, it decreased, as already mentioned, by 90-110 m, and in the interglacial period it increased to +10 ... 4-20 m to the current level.
The Pleistocene is not the only period during which there were significant fluctuations in ocean levels. In fact, they marked almost all geological epochs in the history of the Earth. Ocean level has been one of the most unstable geological factors. And this has been known for quite some time. After all, ideas about the transgressions and regressions of the sea were developed back in the 19th century. And how could it be otherwise, if in many sections of sedimentary rocks on platforms and in mountain-folded areas clearly continental sediments are replaced by marine ones and vice versa. The transgression of the sea was judged by the appearance of the remains of marine organisms in the rocks, and the regression was judged by their disappearance or the appearance of coals, salts or red flowers. Studying the composition of faunistic and floristic complexes, they determined (and still determine) where the sea came from. The abundance of heat-loving forms indicated the intrusion of waters from low latitudes, the predominance of boreal organisms spoke of transgression from high latitudes.
In the history of each specific region, its own series of transgressions and regressions of the sea were distinguished, since it was believed that they were due to local tectonic events: sea waters associated with downfalls earth's crust, their departure - with its uplifting. In application to the platform regions of the continents, on this basis, a theory was even created oscillatory movements: the cratons either fell or rose in accordance with some mysterious internal mechanism. Moreover, each craton obeyed its own rhythm of oscillatory movements.
It gradually became clear that transgressions and regressions in many cases manifested themselves almost simultaneously in different geological regions of the Earth. However, inaccuracies in the paleontological dating of certain groups of layers did not allow scientists to come to a conclusion about the global nature of most of these phenomena. This conclusion, unexpected for many geologists, was made by the American geophysicists P. Weil, R. Mitcham and S. Thompson, who studied the seismic sections of the sedimentary cover within the continental margins. Comparison of sections from different regions, often very distant from each other, helped to reveal the confinement of many unconformities, hiatuses, accumulative or erosional forms to several time ranges in the Mesozoic and Cenozoic. According to these researchers, they reflected the global nature of ocean level fluctuations. The curve of such changes, constructed by P. Weil et al., makes it possible not only to single out the epochs of its high or low standing, but also to estimate, of course, in the first approximation, their scales. Strictly speaking, this curve summarizes the experience of geologists of many generations. Indeed, one can learn about the Late Jurassic and Late Cretaceous transgressions of the sea or its retreat at the turn of the Jurassic and Cretaceous, in the Oligocene, Late Miocene, from any textbook on historical geology. Perhaps what was new was that now these phenomena were associated with changes in the level of ocean waters.
The scale of these changes was surprising. Thus, the most significant marine transgression, which flooded most of the continents in the Cenomanian and Turonian times, was believed to be due to a rise in the level of ocean waters by more than 200-300 m above the modern one. The most significant regression that took place in the middle Oligocene is associated with a drop in this level by 150-180 m below the modern one. Thus, the total amplitude of such fluctuations in the Mesozoic and Cenozoic was almost 400-500 m! What caused such grandiose fluctuations? You can’t write them off as glaciations, since during the late Mesozoic and the first half of the Cenozoic, the climate on our planet was exceptionally warm. However, many researchers still associate the Middle Oligocene minimum with the onset of a sharp cooling in high latitudes and with the development of the Antarctic ice sheet. However, this alone, perhaps, was not enough to lower the ocean level immediately by 150 m.
The reason for such changes was tectonic restructuring, which led to a global redistribution water masses in the ocean. Now we can offer only more or less plausible versions to explain fluctuations in its level in the Mesozoic and early Cenozoic. Thus, analyzing the most important tectonic events that occurred at the turn of the Middle and Late Jurassic; as well as the Early and Late Cretaceous (with which the long rise of the water level is associated), we find that it is these intervals that were marked by the opening of large oceanic depressions. In the Late Jurassic, the western arm of the ocean, Tethys (the region of the Gulf of Mexico and the Central Atlantic), was born and rapidly expanded, and the end of the Early Cretaceous and most of the Late Cretaceous epochs were marked by the opening of the southern Atlantic and many basins of the Indian Ocean.
How could the initiation and spreading of the bottom in young oceanic basins affect the position of the water level in the ocean? The fact is that the depth of the bottom in them at the first stages of development is very insignificant, no more than 1.5-2 thousand meters. The expansion of their area occurs due to a corresponding reduction in the area of ancient oceanic reservoirs, which are characterized by a depth of 5-6 thousand meters. m, and in the Benioff zone, sections of the bed of deep-sea abyssal basins are absorbed. The water displaced from the disappearing ancient basins raises the general level of the ocean, which is recorded in the land sections of the continents as a transgression of the sea.
Thus, the breakup of continental megablocks must be accompanied by a gradual rise in ocean level. This is exactly what happened in the Mesozoic, during which the level rose by 200-300 m, and maybe more, although this rise was interrupted by epochs of short-term regressions.
Over time, the bottom of the young oceans in the process of cooling the new crust and increasing its area (the Slater-Sorokhtin law) became deeper and deeper. Therefore, their subsequent opening had much less effect on the position of the level of ocean waters. However, it inevitably had to lead to a reduction in the area of the ancient oceans and even to the complete disappearance of some of them from the face of the Earth. In geology, this phenomenon is called the "collapse" of the oceans. It is realized in the process of convergence of continents and their subsequent collision. It would seem that the collapse of the oceanic depressions should cause a new rise in the water level. In fact, the opposite happens. The point here is a powerful tectonic activation that covers converging continents. Mountain-building processes in the zone of their collision are accompanied by a general uplift of the surface. In the marginal parts of the continents, tectonic activation is manifested in the collapse of the blocks of the shelf and slope and in their lowering to the level of the continental foot. Apparently, these subsidence also cover the adjacent areas of the ocean floor, as a result of which it becomes much deeper. General level ocean waters sinks.
Since tectonic activation is a one-stage event and covers a short period of time, the level drop occurs much faster than its increase during spreading of the young oceanic crust. It is precisely this that can explain the fact that sea transgressions on the continent develop relatively slowly, while regressions usually begin abruptly.
Map of possible flooding of the territory of Eurasia at various values of the probable sea level rise. The scale of the disaster (with a sea level rise of 1 m expected during the 21st century) will be much less noticeable on the map and will have almost no effect on the life of most states. Zoomed in areas of the coasts of the North and Baltic Seas and southern China. (The map can be enlarged!)
Now let's look at the issue of MEAN SEA LEVEL.
Surveyors performing leveling on land determine the height above "mean sea level". Oceanographers who study sea level fluctuations compare them to the marks on the shore. But, alas, even the “average long-term” sea level is far from constant and, moreover, not the same everywhere, and the seashores rise in some places and fall in others.
The coasts of Denmark and Holland can serve as an example of modern land subsidence. In 1696, in the Danish city of Agger, a church stood 650 meters from the shore. In 1858, the remains of this church were finally swallowed up by the sea. During this time, the sea advanced on land at a horizontal speed of 4.5 m per year. Now on the western coast of Denmark, the construction of a dam is being completed, which should block the further advance of the sea.
The low-lying shores of Holland are exposed to the same danger. The heroic pages of the history of the Dutch people are not only a struggle for liberation from Spanish rule, but also a no less heroic struggle against the advancing sea. Strictly speaking, here it is not so much the sea that advances, but the sinking land recedes before it. This is clear even from the fact that middle level full waters on about. Nordstrand in the North Sea from 1362 to 1962 rose by 1.8 m. The first benchmark (altitude mark) was made in Holland on a large, specially installed stone in 1682. soil subsidence on the coast of Holland occurred at an average rate of 0.47 cm per year. Now the Dutch are not only defending the country from the onset of the sea, but also reclaiming land from the sea, building grandiose dams.
There are, however, places where the land rises above the sea. The so-called Fenno-Scandinavian shield after liberation from heavy ice Ice Age continues to rise in our time. The coast of the Scandinavian Peninsula in the Gulf of Bothnia is rising at a rate of 1.2 cm per year.
Alternate subsidence and rise of coastal land are also known. For example, the shores of the Mediterranean Sea fell and rose in places by several meters even in historical time. This is evidenced by the columns of the temple of Serapis near Naples; marine lamellar-gill mollusks (Pholas) have burrowed into them up to the height of human growth. This means that since the construction of the temple in the 1st c. n. e. the land sank so much that some of the columns were submerged in the sea, and probably for a long time, since otherwise the mollusks would not have had time to do such a great job. Later, the temple with its columns again emerged from the waves of the sea. According to 120 observation stations, the level of the entire Mediterranean Sea has risen by 9 cm in 60 years.
Climbers say: "We stormed a peak so many meters above sea level." Not only surveyors, climbers, but also people who are not at all connected with such measurements are accustomed to the concept of height above sea level. She seems unshakable to them. But, alas, this is far from the case. The ocean level is constantly changing. It is swayed by tides caused by astronomical causes, wind waves excited by the wind, and as changeable as the wind itself, wind revolvers and water surges off the coast, changes in atmospheric pressure, the deflecting force of the Earth's rotation, and finally, the heating and cooling of ocean water. In addition, according to the studies of Soviet scientists I. V. Maksimov, N. R. Smirnov and G. G. Khizanashvili, the ocean level changes due to episodic changes in the speed of the Earth's rotation and the displacement of its axis of rotation.
If only the upper 100 m of ocean water is heated by 10 °, the ocean level will rise by 1 cm. Heating by 1 ° of the entire thickness of ocean water raises its level by 60 cm. Thus, due to summer heating and winter cooling, the ocean level in middle and high latitudes subject to significant seasonal fluctuations. According to the observations of the Japanese scientist Miyazaki, the average sea level off the western coast of Japan rises in summer and falls in winter and spring. The amplitude of its annual fluctuations is from 20 to 40 cm. Level Atlantic Ocean in the northern hemisphere begins to rise in summer and reaches a maximum by winter, in southern hemisphere reverse is observed.
Soviet oceanographer A. I. Duvanin distinguished two types of fluctuations in the level of the World Ocean: zonal, as a result of the transfer warm waters from the equator to the poles, and monsoon, as a result of prolonged surges and surges excited by monsoon winds that blow from the sea to land in summer and in reverse direction in winter.
A noticeable inclination of the ocean level is observed in areas covered by ocean currents. It is formed both in the direction of the flow and across it. The transverse slope at a distance of 100-200 miles reaches 10-15 cm and changes along with changes in the speed of the current. The cause of the transverse slope of the surface of the current is the deflecting force of the Earth's rotation.
The sea also reacts noticeably to changes in atmospheric pressure. In such cases, it acts like an "inverted barometer": more pressure - lower sea level, less pressure - higher sea level. One millimeter of barometric pressure (more precisely, one millibar) corresponds to one centimeter of sea level.
Changes in atmospheric pressure can be short-term and seasonal. According to the studies of the Finnish oceanologist E. Lisitsyna and the American J. Patullo, level fluctuations caused by changes in atmospheric pressure are isostatic in nature. This means that the total pressure of air and water on the bottom in a given section of the sea tends to remain constant. Warm and rarefied air causes the level to rise, while cold and dense air causes it to fall.
It happens that surveyors are leveling along the seashore or overland from one sea to another. Arriving at the destination, they discover a discrepancy and begin to look for an error. But in vain they rack their brains - there may not be a mistake. The reason for the discrepancy is that the level surface of the sea is far from equipotential. For example, under the influence of the prevailing winds between the central part of the Baltic Sea and the Gulf of Bothnia, the average difference in level, according to E. Lisitsyna, is about 30 cm. Between the northern and southern parts of the Gulf of Bothnia at a distance of 65 km, the level changes by 9.5 cm. the difference in level between the sides of the Channel is 8 cm (Creese and Cartwright). The slope of the sea surface from the English Channel to the Baltic, according to Bowden's calculations, is 35 cm. Level Pacific Ocean and the Caribbean Sea at the ends of the Panama Canal, which is only 80 km long, differs by 18 cm. In general, the level of the Pacific Ocean is always slightly higher than the level of the Atlantic. Even if moving along the Atlantic coast North America from south to north, a gradual rise in level by 35 cm is found.
Without dwelling on the significant fluctuations in the level of the World Ocean that occurred in past geological periods, we will only note that the gradual rise in the level of the ocean, which was observed throughout the 20th century, averages 1.2 mm per year. It was caused, apparently, by the general warming of the climate of our planet and the gradual release of significant masses of water, bound until that time by glaciers.
So, neither oceanologists can rely on the marks of surveyors on land, nor surveyors on the readings of tide gauges installed off the coast in the sea. The level surface of the ocean is far from an ideal equipotential surface. Its exact definition can be reached through the joint efforts of geodesists and oceanologists, and even then not earlier than at least a century of material of simultaneous observations of the vertical movements of the earth's crust and sea level fluctuations in hundreds, even thousands of points is accumulated. In the meantime, there is no "average level" of the ocean! Or, which is the same thing, there are many of them - each point has its own coast!
Philosophers and geographers of hoary antiquity, who had to use only speculative methods for solving geophysical problems, were also very interested in the problem of ocean level, although in a different aspect. We find the most concrete statements on this subject from Pliny the Elder, who, by the way, shortly before his death while observing the eruption of Vesuvius, rather presumptuously wrote: “There is currently nothing in the ocean that we could not explain.” So, if we discard the disputes of the Latinists about the correctness of the translation of some of Pliny's arguments about the ocean, we can say that he considered it from two points of view - the ocean on a flat Earth and the ocean on a spherical Earth. If the Earth is round, Pliny reasoned, then why does the water of the ocean on the other side of it not drain into the void; and if it is flat, then for what reason does the ocean waters not flood the land, if everyone standing on the shore can clearly see the mountainous bulge of the ocean, behind which ships hide on the horizon. In both cases he explained it this way; water always tends to the center of the land, which is located somewhere below its surface.
The problem of ocean level seemed unsolvable two thousand years ago and, as we see, remains unresolved to this day. However, the possibility is not ruled out that the features of the level surface of the ocean will be determined in the near future by means of geophysical measurements made with the help of artificial earth satellites.
Gravity map of the Earth compiled by the GOCE satellite.
These days …
Oceanologists re-examined the already known data on sea level rise over the past 125 years and came to an unexpected conclusion - if for almost the entire 20th century it rose noticeably more slowly than we previously thought, then in the last 25 years it has grown very rapidly, according to article published in the journal Nature.
A group of researchers came to such conclusions after analyzing data on fluctuations in the levels of the seas and oceans of the Earth during the tides, which are collected in different parts of the world using special tide gauges over the course of a century. The data from these instruments, as scientists note, are traditionally used to estimate sea level rise, but this information is not always absolutely accurate and often contains large time gaps.
“These averages do not correspond to how the sea actually grows. Tide gauges are usually located along the banks. Because of this, large areas of the ocean are not included in these estimates, and if they are included, then they usually contain large "holes", - the words of Carling Hay from Harvard University (USA) are quoted in the article.
As another author of the article, Harvard oceanologist Eric Morrow, adds, until the early 1950s, mankind did not systematically observe sea levels at the global level, which is why we have almost no reliable data on how quickly the world's ocean in the first half of the 20th century.
sources
http://ria.ru/earth/20150114/1042559549.html
http://www.okeanavt.ru/taini-okeana/1066-mif-o-srednem-urovne.html
http://www.seapeace.ru/oceanology/water/68.html
http://compulenta.computerra.ru/zemlya/geografiya/10006707/
Here we examined, and also tried to find out where it is. See what happens and here is the information The original article is on the website InfoGlaz.rf Link to the article from which this copy is made -