The Cretaceous Period longed for almost 80 million years between 145 and 66 million years ago. It was the third and longest period of the Mesozoic Era, and ended with the Cretaceous-Paleogene large mass extinction event.
In the Cretaceous the fragmentation of Gondwana into present-day continents was accelerated and become mostly complete, though they still had very diffrent positions than today. The distance between Africa and Antarctica, Australia and South-America was growing and the Atlantic Ocean widened gradually. During the Late Cretaceous, India also drifted away from Africa and Madagascar, and the Indian Ocean was formed.
The Earth's continents in the Cretaceous Period, 110 mya.
The Cretaceous period was relatively warm. There were no ice-caps at the poles, thus the sea level was higher than today. Though there was glaciation only at the high-latitude mountains, seasonal snowfalls occurred in higher latitudes during the first age of the Cretaceous. However, later in the period the temperatures were higher. One of its reason could be the intense volcanic activity which resulted higher carbon-dioxide levels in the Atmosphere. The weak temperature gradient between the Equator and the polar regions resulted weaker global winds, and thus also led to much weaker ocean currnents. Therefore, oceans were more stagnant than present-day, and they were also much warmer than today.
Flowering plants (angiosperms) appeared during the Early Cretaceous, and after a rapid diversification, they become the dominant element of the Earth’s flora by the end of the period. Conifers also remained significant, however, some other taxa which were inportant during the Mesozoic, like Bennettitales, gone extinct by the end of the Cretaceous.
In the marine fauna, modern sharks, rays and teleosts become more significant. Ichthyosaurs gone extinct by the end of the period due to an anoxic event of marine habitats), but other reptiles, like plesiosaurs thrieved during the entire period, and mosasaurs evolved in the Late Cretaceous and became importand aqatic predators.
Different species from the Cretaceous Hell Creek Formation. Source: By Durbed - http://durbed.deviantart.com/art/Happy-New-Year-from-Hell-Creek-345906630, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=37131266
The dinosaurs remained the predominant elements of the terrestrial fauna, and they reached the peak of their diversity during the Cretaceous. Small-sized mammals became also very diverse, and birds evolved and also started to diversify. During this period pterosaurs started to decline.
The Cretaceous Period was closed by the Cretaceous-Paleogene extinction event, which was a sudden mass extinction about 66 million years ago. The key reason of the event was the impact of a massive asteroid, which devastated the global biosphere. Nevertheless, other factors, like Deccan traps, mass volcanic activity and climate change also might have contributed to the extinction vent. Approximately 75 percent of the plant and animal life forms were eradicated from Earth. This extinction event caused the extinction of dinosaurs, though a handful of their populations might survive and exist on for a short time during the early Tertiary.
The impact of the meteorite which eradicated the dinosaurs. Source: pixabay.com License: Pixabay License. License link: https://pixabay.com/service/license/