Dinosaurs
Dinosaurs were very large crawling animals that have lived on Earth since ancient times and were among the most widespread animal groups on our planet for a period of 160 million years. The dinosaurs, of all kinds, suddenly disappeared from Earth some 65 million years ago. Scientists differed in determining the cause of their extinction. There are still many different interpretations, but a large part of the scientific community tends to agree the cause was the collision of a large asteroid coming from outer space with Earth's surface, where the clouds of scattered dust resulting from the collision blocked the sun’s rays, and therefore causing sudden and severe climate changes on the planet. Many animals were unable to adapt to those changes. The result was the extinction of all kinds of dinosaurs that lived back then, in addition to about 60% of all life forms that existed on the planet at that time.
Age of the dinosaurs
Dinosaurs appeared on the planet at the beginning of the Triassic period, about 230 million years ago, and belong to the reptile group, which also includes turtles, crocodiles, snakes and lizards of various kinds. The diversity of dinosaurs grew at an accelerated pace throughout the post-Triassic ages, becoming one of the largest, most diverse and widespread animals on Earth. But scientists can only recognize these organisms through their fossils and remnants, which are very difficult to find, making it difficult to study. However, since 1824, scientists have discovered more than 1,000 species of dinosaurs that have lived throughout 160 million years of our planet's history. Many unusual animals have lived on Earth together with dinosaurs, which people sometimes mistakenly believe to be dinosaurs, but they actually belong to other species of reptiles. A striking example of these organisms is the so-called Pterosaurs, a very large winged reptile that had wings of some its types up to more than 10 meters wide. Many exotic alien reptiles also lived in the sea, such as the Plesiosauria, which benefited from its long neck catching fish, and the 17-meter-long Mosasaurus, one of the largest carnivores that lived on the planet in history.
Theories about extinction
Although the scientific agreement is moving increasingly towards the idea that an asteroid colliding with the earth was the main factor behind the extinction of the dinosaurs, there are many proposed theories that attempt to explain the disappearance of these organisms off the face of the planet. They are very diverse and varied, some of the most important of these are:
• Asteroid collision: discovered Sediments from the late Cretaceous period indicate that Earth experienced a series of severe seismic waves during the extinction of dinosaurs, an event that could be accompanied by a large collision of an asteroid. On the other hand, abundant amounts of iridium, a very rare chemical element in the earth's crust but widespread in the chemical composition of many outer space asteroids, have been discovered in the same sediments. In addition, many high-shock quartz crystals have been detected in same layers, which strongly supports such a theory. In such a case, the impact of an asteroid impact on the Earth will not be the primary cause of extinction, but rather the debris of the asteroid, which is likely to have evolved into a giant dust cloud into the atmosphere, blocking sunlight and thus lowering the surface temperature on Earth massively and causing the destruction of vegetation and the elimination of many forms of life, as well as causing severe climatic disturbances, such as thunderstorms, arid and infrared emissions in large quantities.
• Volcanic eruptions: This theory is associated with the belief that the extinction of dinosaurs was gradual. Rather than suddenly occurring 65 million years ago, it could have been an event that took hundreds of thousands or millions of years. Evidence suggests a series of volcanic eruptions West of India (the Deccan Plateau) from 68 million years ago to more than 2 million years later. Volcanoes may have contributed to the extinction of dinosaurs in various ways, such as the release of toxic sulfur gas into the air, or the blocking of sunlight from plants by the heavy smoke they emitted.
• Continental drift: The theory of tectonic plates states that continents are based on separate blocks of land floating above the inner layers of the earth, and that these clusters converge or move away from each other continuously, and it is possible that this phenomenon has played a role in the extinction of dinosaurs, where evidence suggests that The continents were drifting from the equator towards the poles during the Cretaceous period, which may be the cause of climatic changes in different regions, reaching up to six degrees Celsius in some areas. There are, however, several gaps in this theory, such as its inability to explain why dinosaurs could not survive longer near the equator.
• Poisonous plants: This theory suggests the emergence of poisonous plants in the last era of the Cretaceous era, that most plant eating dinosaurs fed on which led to them getting poisoned and die, sequentially causing the death of carnivorous dinosaurs since the prey to feed them became scarce. However, this theory has been rejected by many scientists and researchers for finding it difficult to believe, poisonous plants spread in modern times through many different types and species, but did not cause the extinction of any species of living organisms, this theory also fails to explain the cause of the extinction of marine organisms at the end of the Cretaceous period, which were not affected by those poisonous plants on land.
• Epidemic: This theory assumed the emergence of an infectious germ that affected all types of dinosaurs and spread between them causing death. This theory is weak because it is difficult to have a single germ that affects different types of dinosaurs that differ in strength and ability to fight germs and diseases.
• White robbers: The authors of this theory tended to assume that a rodent appeared in the late Cretaceous period, feeding on the eggs of the dinosaurs in a large and rapid manner, which stopped its propagation, but many scientists found it difficult to accept this theory.
Dinosaurs survive extinction
Although most of the evidence suggests that birds are the only species classified as dinosaurs that survived the Cretaceous extinction, there is little confidence that a small number of them survived shortly afterwards and continued to live in isolated areas. There aren’t many signs of this happening, and many scientists still doubt it, but there are discoveries supporting this theory; scientists have found in a rock formation in the state of Montana dinosaur fossils rising 1.3 meters higher than the rock layer in which the extinction of the Cretaceous period has supposedly occurred in. which means that some species of dinosaurs may have lived up to 40,000 years after the main extinction. However, such discoveries can easily be answered by the fact that the bones found may have been relocated by climate factors, and were incidentally transferred to modern rock layers which, in fact, do not belong to them.
