Photo from open sources
A giant stream of mantle matter rose from the bowels of the earth to north-eastern part of Pangea – where Siberia was located, and melted the stone shell. Eruptions of basaltic lava and ash lasted several thousand years and coincided with the most massive the extinction of animals in the history of the planet. It is frozen strata basalts form the characteristic stepped landscape of many elevations of Eastern Siberia, such as the Putorana plateau. Fig. Olga Orekhova-Sokolova
EASTERN SIBERIA, 251 MILLION YEARS BACK
For a long time, global disasters that could affect the evolution of earthly life was of little interest to scientists. Geologists and it was more important for paleontologists to understand progressive and continuous species change. Only relatively recently, in the middle of the past centuries when it was established that mass extinctions coincide in time with catastrophic events such as outbreaks volcanism and the fall of meteorites, they began to study purposefully.
For the first time about disasters that happened on Earth in the past, French scientist Georges spoke at the beginning of the 19th century Cuvier. A talented paleontologist understood that animals of past eras completely unlike the current ones, for example, bones ichthyosaurs and plesiosaurs are found in certain layers of the Alps and looking for them in later sediments is futile. And bones of manatees and seals, on the contrary, should not be searched next to the remains of ichthyosaurs. As an experienced comparative anatomist, having studied extensive collections mummies of animals and their stone bas-reliefs taken out by soldiers Napoleon from Egypt, he saw that for 2000-3000 years species of animals do not change.
So that in the history of the Earth, as it was then believed, no more than 100,000 years, frequent changes in the species of the animal world took place, we need some destructive short-term events. And Cuvier suggested the idea of periodic catastrophes, the victims of which were countless living beings: “Some of the inhabitants of the land were absorbed floods, others that inhabited the bowels of the water, ended up on land together with a suddenly raised bottom of the sea … ”
A photo from open sources Crater and special rocks found in the area of the Yucatan Peninsula, in the territory of modern Mexico, indicate that an asteroid fell there. His fall caused catastrophic consequences: a blast wave burned out almost all living things in the vicinity, and a monstrous tsunami devastated the coast. The wave carried on coast of marine life such as hidden in a spiral Ammonite mollusks and marine lizards – Mosasaurs. Their remains turned out to be miles from the water and served as food for rare surviving land inhabitants. Upon hitting the earth, the asteroid vaporized and knocked out of the crater a mixture of dust, ash, caustic vapor, which, rising into the atmosphere, poisoned her and eclipsed the sun. Sharp cooling and acid rain probably lasted several years. it the event was accompanied by the extinction of 35% of the species of marine inhabitants, and also all large reptiles: marine dinosaurs, dinosaurs and pterosaurs. Fig. Olga Orekhova-Sokolova
NORTH AMERICA, 65.5 MILLION YEARS BACK
Scientists returned to the idea of geological disasters 100 years later, when you noticed that the progressive growth of diversity organisms inhabiting the Earth, interrupted by at least two grandiose drops in their numbers. These breaks coincide with the boundaries of geological eras: Paleozoic, Mesozoic and Cenozoic.
The most massive extinction of living things in the entire history of the Earth happened 251 million years ago, at the end of the Paleozoic era. Over 90% of marine and 70% of terrestrial species have forever disappeared from the face of the Earth – only the smallest and simplest remained. In the oceans reef formation, previously widespread throughout seas, and on land – the accumulation of coal, as it covered disappeared lush forests of tree-like plunds, ferns and various ancient gymnosperms. Scientists are looking for the causes of this extinction as in the state of the biosphere itself, and outside it. Among external causes extinction today is most often called a disaster caused by powerful volcanic eruptions in Eastern and partly Western Siberia. It was short in geological scale event, greatly influencing the biosphere. His footprints captured in the form of a vast thickness of basalts, with a capacity of several kilometers, called Siberian traps.
A photo from open sources
In the cliff of the Putorana plateau, the thickness of basalts is clearly visible, poured 251 million years ago in the shortest possible time – thousands of years. The cover of ancient lava in these places reaches a thickness of 1.8 kilometers. Photo: SERGEY FOMIN / RUSSIAN LOOK
They formed for the shortest by geological standards the period of time is approximately 160,000 years, and maybe no more 8000 years. Basaltic lavas covered a maximum of 7 million square kilometers of land. From the depths of 2 to 3 million cubic meters kilometers of volcanic materials, including millions of gigatons carbon dioxide. The content of the latter in the atmosphere of that time increased by 7-10 times. (For example, if humanity this century will burn all fossil fuels, concentration carbon dioxide in the atmosphere will rise 2-3 times.) Moreover, heating of the atmosphere due to greenhouse gases and peculiar clouds in the form of clouds, consisting of large particles volcanic ash and soaring over the entire planet, led to warming the upper ocean and the release of billions of tons methane, until then shackled by ice crystals on the shelf. This gas is one of the most effective greenhouse factors; moreover, it is fast oxidized, taking oxygen from the atmosphere. The overall effect of atmospheric changes was reinforced by a peculiar paleogeography the planet. In those days, all the continents united into one supercontinent – Pangea, stretching from pole to pole. (The Siberian platform was in its northeastern part.) Above central, remote from the coast, vast area supercontinet hardly rained, it was dry and almost lifeless. Land animals focused on the outskirts of Pangea, bordered by mountain ranges, and gradually moved to its southern, Antarctic coast, where there was no too hot. The drop in atmospheric oxygen made life in the mountains is impossible, and only small ones remained inhabited lowlands.
In such an environment, under the most unfavorable conditions most reptiles and fish, as well as calcareous algae, corals, sponges. The first suffered from a lack of oxygen and poisoning carbon dioxide, the second ruined the acidification of sea water caused by dissolving in them an excess of carbon dioxide. Some survived terrestrial amphibians, as well as reptiles, for example, proterozuchia – ancestors dinosaurs, cynodonts – beast-lizards, mammalian ancestors, and listrosaurs are their distant relatives. These were animals. small size, which needed to maintain activity less energy costs, which means they consumed less oxygen. The Listrosaurs had devices that allowed on the contrary, absorb more air, and therefore oxygen, enlarged chest and parts of the skull associated with breathing. Among marine animals, the smallest also survived the disaster. foraminifera, brachiopods, bivalves, as they needed less food and oxygen. Their large relatives disappeared. Terrestrial flora not less affected than the fauna – excretions containing chlorine volcanoes destroyed the ozone layer, hard ultraviolet radiation crippled spores not yet germinated, sulfate rains burned leaves, and the last juices from dying trees sucked proliferated mushrooms. Past biodiversity on Earth recovered only 60 million years later, by the middle of the Jurassic period.
Space factor
In many places on Earth, where the ancient seabed goes to surface, you can see a thin clay layer formed by 65 million years ago. It is along it that geologists draw the border Mesozoic and Cenozoic Eras. A notable example of such a boundary discovered recently in southeastern Spain, near the town Caravaca de la Cruz – thin, a few millimeters layer reddish clay among the many-meter strata of white marls. Below that layer remains of diverse animals inhabiting the sea Mesozoic era: bones of marine dinosaurs, ammonite shells and the smallest planktonic creatures – foraminifera and coccolithophore, from which formed sludge silts, which eventually turned into calcareous rocks – marls. There are also petrified the shells of tiny crustaceans that swallowed clay particles, pressed them into lumps – pellets – and in such a more “weighty” form sent to the bottom, creating a mass of sedimentary material. And suddenly” all these animals disappeared and therefore completely stopped the formation of calcareous sediments, the rate of accumulation of clay particles fell hundreds of times – this is evidenced by low power boundary layer. For several thousand years, the sea remained almost uninhabited, then life took its toll, and the geological record captured her recovery, starting with rampant breeding of few and small surviving species of foraminifera. The shells of their descendants formed new layers of white marl.
A photo from open sources
While in East Africa the ancestors of Australopithecus mastered the savannah, the Mediterranean experienced the strongest ecological crisis. Growing mountain ranges blocked his message with the Indian and Atlantic oceans, due to lack of water the sea gradually dried up. A huge hollow with a depth of up to 5 in places kilometers hundreds of thousands of years remained almost anhydrous. The crisis ended with a sudden breakthrough of Atlantic waters through Gibraltar strait. At the same time, a key role could be played simultaneously by three factors: sea level rise, tectonic processes and erosion of the walls of the basin. Sea water plunged into a hollow, forming the largest waterfalls known today. Drying out and the catastrophic filling of the Mediterranean is captured in many kilometers of salt and gypsum, numerous caves, buried river canyons and stepped bottom topography Strait of Gibraltar. Fig. Olga Orekhova-Sokolova
WESTERN EUROPE, 5.33 MILLION YEARS BACK
What happened on land in these millennia can only guess because the border is clearly traceable to marine strata, in land deposits no. It is well established that the owners sushi – diverse and numerous dinosaurs and pterosaurs – this milestone did not survive.
What events happened 65 million years ago, which divided have geological epochs caused such global changes? IN in search of an answer to this question, scientists turned to space factors. In the mid-20th century, astrophysicists discovered the phenomenon of birth supernovae associated with huge energy surges and paleontologists have suggested that this the released energy, reaching the Earth, could pluck it the magnetosphere that protected the planet from hard radiation, and thereby doom its inhabitants to death. However, to substantiate this hypothesis, studying the geological record, failed.
Also, another idea about a space disaster soon came to life, which quickly gained popularity. American geophysicist Walter Alvarez discovered near the Italian town of Gubbio in a thin a clay layer denoting the boundary of the Mesozoic and Cenozoic eras, unusually high iridium content, hundreds of times higher than average its concentration in ordinary rocks. Walter’s father nuclear physicist Luis Alvarez helped find an explanation for this phenomenon. It turned out that the fragments of meteorites that fell to Earth also contain a lot of iridium and other metals of the platinum group. Mean these elements could get into the clay layer as a result of impact cosmic body.
Alvarez became interested in the coincidence of the time of the alleged the fall of the meteorite and the death of dinosaurs and related these two events in a single hypothesis of an “asteroid winter” by analogy with the “nuclear winter”: if an asteroid crashed into the Earth at a speed of 20 kilometers per second over 10 kilometers across, a monstrous surge occurred 10,000 times more energy than all current nuclear stockpiles earthlings. Part of the Mesozoic inhabitants immediately died from shock and heat waves, the rest are extinct from the effects of the fall – dust soaring into the atmosphere reflected the sun’s rays. Started cooling and vegetation left without light and heat became to die. Then followed the mass extinction of the foodless animals.
After the appearance of a small note by Alvarez in 1980 in Science magazine the number of scientific articles on global disaster, has grown hundreds of times. First searched evidence of the correctness of physicists who have affected the interests of paleontology. And they found a lot: in almost all sections, where the boundary layer 65 million years old is quite well expressed, marked iridium anomaly, as well as shock quartz crystals – small parallel cracks that occur with a very large pressure, tektites (chilled drops of the melt formed during impact of a large meteorite on rocks), interlayers of soot. Discovered and the Chicxulub Crater in Mexico, whose time of occurrence is approximately coincides with this border.
Mediterranean flood
Georges Cuvier considered the prime cause of global extinctions floods, but this hypothesis has not been confirmed by modern geologists. To flood all land except high mountains, and destroy large part of the land inhabitants, at least two conditions are necessary: hundreds of meters increase in sea level and transience events. Nowadays, when the average height of the continents above the level of the sea is 670 meters, it is necessary that the volume of the World Ocean almost doubled. Such an event never in earthly history did not happen and due to the lack of such free water reserves hardly possible in the future.
Two main phenomena regulate the level of the oceans – change in the area of continental glaciers and mid-ocean ranges (high mountain ranges located in the central parts all oceans). Proliferation of glaciers incorporating huge water masses, and the compression of mid-ocean ridges lead to that oceans and seas are retreating, draining vast territories the shelf. Reverse processes – melting glaciers and network expansion seamounts pushing water out of the ocean, contribute to sea level rise. Coincidence of these two factors can cause a very significant rise in the sea like this happened in the middle of the Cretaceous, about 90 million years back. According to recent estimates, then the level of the oceans rose 250 meters, flooding vast tracts of land. However consider it increased catastrophic flood prevents long duration events – millions of years, this is how much the growth of undersea mountain chains. The ocean comes slowly, conquering land by millimeter in year. At this rate, the animal world manages to adapt, and rapid mass extinction does not occur.
A photo from open sources
Cretaceous seabed before it is empty 65 million years ago. On the left are the shells of molluskovrudists, “dinosaurs of the seas” so named for their large size and simultaneous extinction. The diorama is made from genuine paleontological objects, its author is Santiago Lafarga. A photo: ANDREI ZHURAVLEV
Local floods, i.e. rapid flooding of land, occurred in the past repeatedly, but at a very limited space – they never covered the whole planet no damage to the inhabitants of the land. The largest reliably confirmed flood happened just 6 million years ago on the territory of the Mediterranean. By then, due to isolation from Indian and Atlantic oceans the Mediterranean Sea is dry turning into a vast hollow, almost 5 places deep kilometers relative to the level of the oceans. Her bottom gradually filled with a three-kilometer layer of gypsum and salt formed in the process of evaporation of sea water, and in warm brines shallow lakes preserved in some places could survive only special bacteria are haloarchaea.
This stage in the history of the region is called the Messinian crisis – according to the name of the province in Sicily, where salt was mined from ancient times. Geologists very accurately established the time when the Messinian crisis came to the end – it happened 5.33 million years ago when the waters Atlantic Ocean began to penetrate tectonic fissures across the west side of the basin. At some point, the water flowed into the rocks are quite wide – the current Strait of Gibraltar – and poured a waterfall into a dry, saline lowland. Filling The Mediterranean Sea was very fast – only 15,000-20,000 years during which ordinary marine communities settled in it. The catastrophically fast flood hypothesis in the basin One of the first to express the Mediterranean Sea was the Soviet geologist Ivan Chumakov, who worked on the construction of the Aswan Dam in Egypt in 1970s and discovered according to drilling the ancient channel of the Nile, filled with marine sediments. Messina flood significantly influenced the climate in their region, but to significant realignments in the biosphere did not.
In neocatastrophism – the so-called updated Cuvier theory – a lot of assumptions, not yet actual evidence. If the existence of epochs of powerful volcanism is not is doubtful, because they left unambiguous traces in the earth crust, then prove the fall of the asteroid and especially the exact time of this falling is not easy. In addition, in both cases it is extremely difficult. establish exactly how the consequences of the disaster led to extinction species. There is no explanation yet for the fact that some major disasters (e.g. basalt outflows in South America and Africa 130 million years ago) did not lead to the mass death of living organisms. Not for all major extinctions in the history of the Earth (their there are six) were able to find catastrophic reasons – volcanic, space or some other. Due to lack It’s still hard to judge how strong the impact of disasters on evolution of life, however scientists, even those who support neocatastrophism, agree on one thing: and the most destructive of ancient catastrophes could not destroy earthly life completely. There was always someone who gave rise to new inhabitants the planet.
Andrey Zhuravlev
Africa Water Time Dinosaurs Egypt Life Crisis Mexico Siberia Evolution
