HarrisonGrey's+Cretaceous+Period

__The Dusk Of The Dinosaurs__ (The Cretaceous Period) By: Michael Hume See My Text Bibliography See My Photo Biography See My Reflection

Introduction: The Cretaceous period started 144 million years ago and ended 65 million years ago. When you think of the Cretaceous Period, you think dinosaurs. However the largest dinosaurs thrived during the [|Jurassic] period. When Pangaea continued to break apart. Sea levels rose, and the very first birds and flying retiles appear. So you think that since the Cretaceous period doesn’t have big dinosaurs it isn’t cool. Wrong again, during the Cretaceous period the continents moved toward where they are today. Volcanic activity occurs throughout the continents. The first flowering plants appeared, while dinosaurs dominate. Snakes appear and survive through the mass extinction that completely wiped out all dinosaurs. Then came along what we know as the Tertiary period. During this period the most famous mountains such as the Rockies, and the Alps form. Glaciers cover Antarctica about 25 million years ago. Flowering plants developed to more extreme plants. Grasses and mammals develop into more extreme animals. Primates such as horses and elephants appear. Mammals return to the ocean in forms of whales and dolphins. Ancestors of you and I developed into hominids. Glaciers cover part of North America about 2.5 million years ago. You see… the Cretaceous period is cool… in it’s own way.

Abiotic: In one of the epochs in the Cretaceous called the Berriasian epoch, there was a cooling trend that started in the late Jurassic. There was more snowfall in the higher altitudes and the tropics became wetter than the Jurassic. There were only alpine glaciers on some high-latitude mountains. At the end of the Berriasian epoch, temperatures increased once again. The temperature was consistent from here on in during the Cretaceous period. This high temperature trend was due to volcanic activity, which released large quantities of carbon dioxide into the atmosphere. The large amounts of magma made the tectonic plates shift rapidly. This made most of the seas rise up and that made the landmasses be covered by shallow seas.

Landforms: Since there were shallow seas on top of most of the landmasses, a lot of the stone that was from Cretaceous period was marine limestone. Chalk is one of the rock types that are commonly found in the Cretaceous. The continents consisted of all seven continents we have today, yet there are many differences. Such as Asia and Europe are not connected, during the Cretaceous period there was a sea that ran right through the point were they connect today. Massachusetts is very close to were it is today. If the Rocky Mountains were there during the Cretaceous, they would be in the exact same point of longitude they are today.

Biotic: Flowering plants spread during this period; their evolution was aided by the appearance of bees. The first representatives of most leafy trees such as figs, planes and magnolias, appeared in the Cretaceous. Marine life flourished with animals such as the woolungasaurus and the hesperotnis. The mammals on land were a small and still relatively minor component to life during the Cretaceous. Primitive marsupials evolved in the E arly Cretaceous. Some of the most dominant creatures were reptiles, big reptiles… the dinosaurs. One of the most common reptiles in the Cretaceous period was the pterosaur. The pterosaur was a flying reptile that dominated the skies in search of food for their young. The tyrannosaurus rex is one of the most well known dinosaurs in the world. This giant lizard is a fierce carnivore that will eat practically anything. These two dinosaurs were examples of carnivores. There were also herbivores such as the triceratops. During the Cretaceous omnivores were the outsiders. The three levels of the food chain lived in completely different environments. I talk about all this life and happiness and glee, but come the end of the Cretaceous period there is no such thing.

A Mass Extinction: A mass extinction created by a meteor the size of the empire state building crashed into earth and a speed of 65,000 mph. If all life on earth wasn’t dead by then, just wait until you hear the next part. Soot mixed with the oxygen in the air to make a poisonous atmosphere. All dinosaurs were either killed on impact or choked to death because of the toxic oxygen. Now all that is left were what evolved into us. If some creatures didn’t survive the extinction you and I would not be were we are right at this exact moment.