Life on Earth in Cretaceous Period

The Cretaceous period is the last epoch,the final Mesozoic era. He changed the Jurassic, according to geologists, somewhere around 145 million years ago and lasted about eighty million years, after which the tertiary period of another, the Cenozoic era, "the era of a new life" began. The name of this rather long stage of the Earth's development was due to the fact that it left us a legacy of powerful deposits of chalk, marl and sand. Although during these eighty million years there have not been any catastrophes of a planetary scale and, consequently, the extinction of a large number of plant and animal species on Earth, yet the movement of tectonic plates, the change in the level of the world's oceans and the change of climate have made their corrections in the evolution of living beings .

Cretaceous period is divided into sub-sections: lower and upper chalk. To understand how life developed in the seas, on land and in the airspace of that time, it is necessary to briefly describe the tectonic mountain-forming processes that took place since the Jurassic stage. In the Lower Cretaceous, Gondwana and Laurasia continued to move away from each other. The same process took place with Africa and South America. Thus, the Atlantic Ocean acquired more and more familiar shapes. But in the east, Gondwana united with Laurasia. Australia was where it is now, but only a third of the present territory was rising above the water.

Upper chalk is characterized by the fact that in the Northernhemisphere, the level of the world ocean began to rise, and the vast areas of Eastern Europe, Western Siberia, the whole of Arabia and almost all modern Canada were under water. However, by the end of the Cretaceous period, the Earth began to resemble with its outlines a modern globe.

In the Cretaceous period, the climate changed. Of course, it was much warmer than the modern one. Spaces of today's Europe covered the real tropical jungle. However, in the high latitudes the seasons have already changed, and in the winter snow has fallen. Such climate change gave the impetus to the fact that, along with spore and gymnosperms, there were occlusive plants. Such trees as beech, birch, ash and walnut, appearing in the era of the chalk, have survived to this day unchanged. The earth has found the first flowering plants - first magnolias, then roses. The flowers had the advantage that not only the wind but also the insects carried their pollen. Fruit plants, hiding the seed in the fruit, spread with the help of animals that ate fruits. Thus, fruit and flowering plants flooded the entire planet.

Changes in the flora in the Cretaceous period entailed andthe emergence of new species of fauna. The first butterflies began to flutter in the air and the bees that feed on the nectar of flowers fly. In the sea comes dominance foraminifera, dead and crumbled shells which gave the name to all this geological time. Along with them there are other molluscs-ammonites. The fish kingdom is dominated by sharks and bony fishes. Animals of the Mesozoic era - first of all, dinosaurs and the first mammals - safely "migrated" from the Jurassic period to the Cretaceous. But during the chalk several dead-end branches of bird-like lizards die, for example, archeopteryxes. But there are birds - the ancestors of modern geese, rzhanok, ducks and eiders.

Mesozoic era (Jurassic period in particular),judging by the famous film, is also known as the era of dinosaurs. In general, the primacy of the ancient lizards is preserved in the chalk. But during the last period the stegosaur disappears from the face of the earth, and its niche is occupied by a tyrannosaurus. The rich plant world contributed to the emergence of new species of herbivorous dinosaurs: triceratops, iguanodons, ankylosaurs and others. We can say that in the Cretaceous, the species diversity of dinosaurs reached its peak. And at this time, hiding from the giants by their burrows, the future masters of the Earth - mammals - also lived. These animals, like rats, rarely reached one meter in length, most of the species were small oviparous, shell or marsupial animals, up to 500 grams in weight. But behind them was the future.