Why did the dinosaurs become extinct?

The darkness that prevailed in the years after the asteroid hit caused the destruction of most of the animal and plant species that lived on Earth at that time. In an article published in the International Journal of Earth Sciences, Dr. Zeev Levy, a researcher at the Israel Geological Institute, explains that the ones who directly caused the extinction were the characteristics of the animals themselves in response to the ecological crisis. This explains why there were groups of animals that survived

Dr. Zeev Levy*
In the study of ancient life on Earth (paleontology) a noticeable change was noticed in the fossil assemblages of animals and plants between two sequences of layers. Fossils that were common in the lower layers disappeared as if all at once, and in the layers above (younger) new species of flora and fauna appeared along with some survivors. Disappearance of species and types while new ones appear has occurred in the past as part of the development of life (evolution), and with their help researchers distinguish between ancient and younger periods. The disappearance of many species at once (on a geological scale) is unusual in the history of the earth and indicates a sharp change in living conditions to the point of ecological disaster. Prominent events like these distinguish between three geological eras. The first includes early life and is called the Paleozoic. The middle age of life is the Mesozoic, and the new one is called the Cenozoic.

A change in the fossil collection between the Mesozoic and the Cenozoic occurred 66 million years ago and is characterized by the disappearance of many creatures with a diverse lifestyle on land, in the sea and in the air, which makes it difficult to decipher the mystery. The large terrestrial reptiles, the dinosaurs, that dominated the continents for about 150 million years and evolved into gigantic forms and swift and ferocious predators stand out. This image made them "stars" in movies and television and in commercials, which were admired by children and youth at the same time as their scientific research. Findings of dinosaurs are not common, usually only single bones are found, while the finding of a complete skeleton becomes an event that excites the scientific community and the general public. The disappearance of these super creatures raised imaginative hypotheses and unsuccessful scientific attempts, which did not fit in with the disappearance of certain creatures compared to the survival of other creatures. Any destructive physical or toxic chemical agent that might have exterminated certain organisms was rejected by the survival of organisms sensitive to that agent. The selectivity of the extinctions has not been deciphered so far, nor the duration of the ecological crisis, and especially not what caused the disappearance of the dinosaurs in this crisis. All of these were clarified in the author's research published in the December 2016 issue of the International Journal of Earth Sciences).

Today, researchers agree that during the transition between the two eras there was extensive volcanic activity in the Deccan Plateau region of India, where more than three thousand meters of tuff and basalt accumulated, that the emission of toxic gases and ash could have damaged the climate and living conditions around the world.

In 1980, Alvarez and his colleagues published that they had found unusually high concentrations of the element iridium in a thin layer of marine chalk in various parts of the world exactly at the border between the two eras, that is, at the end of the Mesozoic era, which is the end of the Cretaceous period (no explosions of kirton rocks). This element is rare on Earth and known in bodies that come from outer space such as meteorites. Therefore, the researchers proposed that a giant asteroid hit the Earth and exploded into particles down to dust and gases, which, together with terrestrial material, took off into the upper atmosphere in large quantities. They masked the sun's radiation and darkened the whole world, as evidenced by the disappearance at the end of the Cretaceous of all living plankton and marine plants, whose cells contain assimilating (photosynthetic) algae that need the sun's radiation for their activity and life. In this assimilation activity in the field of light penetration in the oceans (the photic field), carbon dioxide is absorbed and oxygen is released into the upper waters while also releasing it into the atmosphere. In part, the oxygen mixed with the deep water and life was possible even below the light penetration range. These tiny creatures were in the past, and are still today (new species) an important source of oxygen in the atmosphere and the marine environment, and also the basis of the food chain in the oceans. Their death within a few weeks of darkness severely damaged the food chain while the decline in oxygen concentrations was slow.

The darkness also stopped the assimilation activity of the land plants, but the disruption of the food chain there was more gradual. A few years after the publication of this presumed extinction mechanism, they discovered in the subsurface of the Yucatan Peninsula in Mexico a crater with a diameter of about 180 kilometers into deep sea sediments from the end of the Cretaceous period, indicating the impact of a large asteroid with a diameter of about ten kilometers. The impact at sea reduced the destruction that could have occurred from an impact on land, although evidence was found of tsunami waves that carried sand to remote areas. At the same time, research continues (researchers from Princeton University, USA) on the effect of the volcanism products of the Deccan region on global ecosystems.

Analyzes of oxygen isotope ratios in calcareous skeletons of single-celled animals from the Late Cretaceous have revealed in various parts of the world an increase in the temperatures of the upper and deep sea water by 30-50 that lasted about 250 thousand years. This warming was attributed to the greenhouse effect due to the masking of the earth by the ash and volcanic gases from the Deccan region in India, which prevented the emission of the heat of solar radiation. Although this disturbance weakened and disappeared about a hundred thousand years before the end of the Cretaceous, the group of researchers continued to adhere to the theory that volcanism and not the impact of the asteroid caused the biological-ecological crisis and extinctions at the end of the Cretaceous. However, when the abnormal appearance (anomaly) of iridium in the sea sediments of the end of the Cretaceous was discovered in northeastern India at the edge of the volcanic zone, the researchers agreed that these two factors were probably responsible for the extinctions, without explaining how this is consistent with the drop in the temperature of the ocean water to its normal temperature about a hundred thousand years ago The asteroid hit.

The devastating impact of a giant asteroid hitting the Earth is now accepted by most researchers, but what actually happened, why the extinctions are selective, how they happened and how fast have not been understood until now. In 2015, the author of this article proposed that the collision waves of the large asteroid in what is now the Yucatan Peninsula (Mexico) shocked the trending cell in the Deccan region, which was then almost on the other side of the Earth, and renewed the volcanic activity. The emissions of both together raised a huge amount of ash and gases, with the continuation of the emission of hot volcanic gases over several years slowing down the fallout of the particles from the asteroid's explosion and the molten terrestrial material from its impact. That's why the masking of the sun's radiation lasts far beyond a few months to about a year, which is known from unusual historical volcanic eruptions themselves.
Darkness of several weeks is enough to harm the assimilating creatures
in a sea whose life span is short. On the other hand, on land, the darkness of at least 3-2 years is needed to stop the growth of annual plants and the shedding of leaves even from non-deciduous trees while stopping the pollination of flowers and the formation of fruits and seeds. The lack of lighting over such a period damaged the seasonality that activates the breeding cycles of the animals, when the lack of births reduced the food of the predators. It is likely that within 3-2 years the number of animals decreased and the terrestrial food chain was damaged due to the reduction of fresh vegetation and the amount of prey. Geological evidence of the short time of the Dark Age and the global biological crisis was found in a continental-swamp sediment of layers of coal and chalky clay, containing plant pollen (pollen) and fern spores from the end of the Mesozoic, and on top of them appear pollen and spores known from the beginning of the Cenozoic.
The palynological boundary (according to a change from the pollen collectors) passes through a layer of coal, which, along a centimeter, was found to be enriched in the element iridium. In the lower 4 mm of this thin layer there are no flower pollen or fern spores but a wealth of fungi, which together indicate a period of lack of growth and flowering compared to the decay of the organic matter on the ground and the development of fungi. This fungus-decay layer was also located in the USA at the border between the ages so that this ecological crisis was global. It must be assumed that the first particles that fell passed through the cloud layers and formed condensation centers that resulted in a lot of rain. Together with the lack of solar radiation, they caused moisture on the surface of the ground and mushroom blooms on the surface of the earth. The shedding of the small iridium-bearing particles lasted a few years so that the period of total darkness represented by the mushroom layer was short.
The rapid damage to the food chain in the oceans and the gradual damage on the continents caused struggles for existence between the animals and overpredation of those who could not hide and continue to exist in alien environments with the remaining food. Examining the lifestyle and tolerance of the animals of the Upper Cretaceous to this ecological disaster shows that all those who could not cope with it disappeared. It was an extremely accelerated course of the evolutionary process of natural selection according to Charles Darwin, when the causes of extinction were the animals themselves and not any chemical or physical factor. It is true that in the late Cretaceous (Maastrichtian period) global ecosystems were undermined due to volcanism in the Deccan region and fertility decreased which increased predation pressures. This is manifested, for example, in strengthening the skeletons of ammonites, changing the way of life of Novartis crabs and reducing the breeding areas of the rudists (shellfish with a thick skeleton) that lived on the bottom of the shallow sea exposed to predators. This deterioration in living conditions and the disappearance of a number of animal species occurred over hundreds of thousands of years, this is in contrast to the collapse of living systems within a few years that resulted in the disappearance of groups of animals and plants due to the asteroid impact.

The disappearance of the dinosaurs at the same time as the cessation of assimilation activity in the sea and on land due to a period of darkness lasting about 3-2 years suggests that perhaps these reptiles were cold-blooded (as opposed to their bird relatives). All the spawning sites of dinosaurs were found along ancient beaches, floodplains of rivers in flat lowlands and on low (sandy) dunes, indicating life in flat spaces without tall vegetation where they could look at distances and identify predators, but also absorb the sun's rays at sunrise if they were cold-blooded .
The survival of other blood-blooded reptiles such as crocodiles, turtles, lizards and snakes is explained by their ability to hide from predators among the plants or in the water, when some of them slowed down their metabolism and reduced their diet to what they found in their environment. In contrast, the dinosaurs were naked, especially the largest ones, and after a short period without the solar radiation that gives them energy, they rested on the ground unable to eat or protect themselves from predators. The logical conclusion that the dinosaurs disappeared while the earth went dark for two or three years because they were cryo-blooded has been challenged by discoveries of dinosaur bones and pulleys at high latitudes, which were in the Cretaceous in the arctic and antarctic polar regions. The earliest (about 127 million years ago) were discovered in northern Norway, and younger ones from two periods of the Lower Cretaceous were found in southeastern Australia. Artifacts from the Upper Cretaceous have been discovered in New Zealand, but particularly large concentrations of bones have been found in North America and northern Russia in layers from about 69-73 million years ago. These sites yielded thousands of well-preserved individual bones that were concentrated along a layer. The wealth of these findings surprised the researchers who persisted in digging at these sites and uncovering the fossilized bones while discovering new species and types for science.

Among the skulls were large eye sockets, which were attributed to an anatomical adaptation to the lack of sunlight during the half-year winter at the poles. In doing so, they established the hypothesis that these are populations of "polar dinosaurs" adapted to life at the poles throughout the year. In recent years, the global climate in the Cretaceous (especially the upper) has been reconstructed and it has been found that higher temperatures prevailed than today with up and down fluctuations and ice-free poles. Therefore, the "polar dinosaurs" needed to overcome six months of a completely dark winter. One researcher pointed out that the dinosaurs had the ability to run and migrate and it is unlikely that they stayed in an unfriendly environment to the point of risking their lives, but this reasoning did not stop the researchers from continuing to point out that they were permanent residents of the poles.
The concentrations of bones in the North of the USA (Alaska) yielded along the layer over four hundred skulls and thousands of bones in excellent preservation that showed no signs of wear and tear. Therefore, some researchers have suggested that the dinosaur population was surprised by a flood of water and mud from melting snow and ice, which buried it to death. This reconstruction of the process of bone accumulation provided a reference for the existence of dinosaurs in the poles, which was strengthened over thirty-five years of increased sampling. The existence of dinosaurs at the poles throughout the year was tested on the bone structure, which changes with the rate of activity and nutrition from a spacious structure in rapid growth to a dense-compact structure in slowing growth under harsh conditions of existence. Comparing the bone structure of the "polar dinosaurs" to their relatives who lived in high latitudes outside the Arctic Circle did not show any significant difference.

Despite this, the researchers preferred to accept the theory that the dinosaurs went through the dark winter sleeping, without considering the mobility of the dinosaurs. The attempt to explain the accumulation of bones by burying herds of dinosaurs under a flood of mud raises questions. If indeed a flood covered a living population of dinosaurs then whole bodies were buried. In order for concentrations of individual bones to be obtained, the corpses had to be exposed, the skin (in some species quite difficult) and the flesh to be digested, and the complete skeleton had to be decomposed without noticeable damage to the bones and without scattering, all this before the next covering. That's why the explanation given is wrong, and you need to find another logical explanation for the concentrations of the bones. In 2016, I proposed a new explanation, which rejected the assumption of the existence of "polar dinosaurs" and established the reason for the disappearance of the dinosaurs being cold-blooded in contrast to their warm-blooded bird relatives.

Finding dinosaur remains at high latitudes of 50-60 degrees indicates that these reptiles also existed there in winter, which according to the research was warmer than today, but must have been dark for many days due to cloud cover. Activity in such weak lighting led over time to the development of particularly large eyes and the growth of eye sockets in the skull of a certain species. In these areas of North America, traces of vegetarian dinosaurs have been found for great distances that migrated in herds.

It is probable that towards the spring and the beginning of the flowering they happened to move into the polar region (above latitude 670). There they discovered that the sun's radiation continues without a break for about six months, a favorable climate and abundant vegetation, which created excellent conditions for the breeding season. This migration for reproductive needs became a constant instinctive move every year, similar to the practice today of certain whales that feed in the summer in the South Pole region on blooms of tiny crustaceans (krill) and towards the winter swim to the tropical region near the equator (northeast Australia) for reproductive needs. The animal breeding season is accompanied by competition for the chance to mate. These fights may end in serious injuries and death of the competitors and the accidental trampling of young people. All of these were eaten by carnivores among the meat-eating dinosaurs and by other carnivores, who discovered this seasonal event to their advantage and visited the place for nutritional needs.

The flesh of the dead was eaten while disassembling the skeletons into individual bones, which accumulated every year in the various polar sites for hundreds or thousands of years. At an Arctic bone site in northern Russia, fragments of dinosaur eggs were found, probably from laying by females who were early to mate and about two months later laid and incubated their eggs. Towards the end of summer, the dinosaurs began their migration back to lower latitudes where they live most of the year. This logical reconstruction matches the findings in the polar regions from the Cretaceous and proves that dinosaurs did not live there all year round but only visited these places for a long and successful breeding season. That is why there were no "polar dinosaurs" who were supposedly permanent residents of the polar regions and survived half a year of total darkness.

The disappearance of the dinosaurs took place during the few years of the masking of solar radiation by the emissions from the asteroid impact and the renewal of volcanism in the Deccan region, as evidenced by the cessation of the assimilation activity of terrestrial plants and marine planktonic creatures, which damaged the food chains on Earth. The disappearance of the dinosaurs in that event indicates that they were cold-blooded, that after a few weeks of the lack of sunlight they lay helpless on the ground exposed to any predator. Their cold-blooded relatives such as the crocodiles, turtles and lizards managed to hide among the plants and in the water from the predators and adapt to the temporary ecological change thanks to their ability to slow down the rate of metabolism in their bodies.

* Zeev Levy. Researcher (retired) at the Israel Geological Survey
lewy@gsi.gov.il

More of the topic in Hayadan:

• • Opinion/ Meteorite impact and extinction of dinosaurs - we should act to prevent man from a similar fate
  • The great extinction that paved the way for the development of the dinosaurs may also have been caused by a meteor
  • Debunking six myths about dinosaurs
  • The mammals almost went extinct with the dinosaurs