How the cretaceous period started. The cretaceous period started with the end of the Jurassic. It was the last of the three periods. It was the longest and most alive of the three periods. The cretaceous period lasted a very long time. It lasted 79 million years. It began 145.5 million years ago. There were new species and were very exotic. It was the time of the largest dinosaurs. It was the beginning for new plants to start growing with the perfect temperatures. The temperature was similar but also different from today. It was more mild and hot all across the world. (“The climate was generally warmer and more humid than today, probably because of very active volcanism associated with unusually high rates of seafloor spreading.”) Most dinosaurs
