The Phanerozoic

The Phanerozoic is the era which began 590 million years ago. This period can be divided into three parts: the Paleozoic, Mesozoic, and Kaenozoic. One of the most important things to happen was the development of organic life. This development is relatively easy to follow for scientists, because animals in the Phanerozoic period mostly had hard parts (shells or skeletons). Unlike the soft parts, fossils of these hard parts can be found today. Besides shells and skeletons, many stones from the Phanerozoic can also be found today. Scientists can draw conclusions from these stones about the climate and the evolution of plants and animals.

The continents

The continents, as we know them now (Europe, Asia, Africa, Oceania, North and South America and Antarctica), were once connected as one. This super continent was called Pangea. Because the continents ‘bumped’ into each other, mountains such as the Appalachians in the United States were created. Within this giant continent, a northern and a southern part was created, separated by a new ocean, the Tethys. The northern part was called Laurasia, whereas the southern part was called Gondwana. Laurasia was later divided into North America, Greenland, Europe and Asia. Gondwana existed from present South America, Africa, India, Australia and Antarctica. During the Jura-era (between 205 and 135 million years ago) the two super continents began to seperate further. The continents slowly moved into their present positions. Africa, the Arabic peninsula and India collided with Europe and Asia. One of the results of this collision was the Himalayas and Mount Everest, the highest mountain on earth (8850 meters). The collision had such impact that the Himalayas are continuing to grow at a rate of a few centimeters per year. During this time, the mountains on the west coast of North and South America and the numerous islands on the eastern coast of Asia, were also born.

The climate

The climate of the Phanerozoic has undergone several fluctuations. During several eras ice masses developed, which even covered land. About 500 million years ago (the Ordovicium), ice covered parts of North Africa and South America. More recently, between 350 and 250 million years ago (the Carbon and the Perm), glaciers covered Gondwana. Following that, 65 million years ago from now, large parts of Antarctica, North America and Europe were also covered by ice.

Life

The oldest fossils that have been found are from the same period as the oldest stones. The oldest fossils are 3.4 billion years old and have bacteria-like, round and fibrous structures. Stromatolites, which are nowadays primarily found in Shark Bay (on the west coast of Australia) and in Yellowstone Park (United States of America), were common in the Archaic and the Proterozoic. The first sponges emerged during the end of the Proterozoic, about 700 million years ago. Generally, the animal kingdom can be divided into two groups: sponges and non-sponges. The big difference is that sponges have no digestive system, such as jellyfish and polyps. In the beginning of the Paleozoic period, an explosive development of the invertebrate non-sponges occured. Fossils show that all invertebrates that exist today, existed 500 million year ago. In the Ordovician, the first vertebrates emerged: fish.

Land habitation

Before the Paleozoic period, there was not an atmosphere as we would know today. It was only during this era that the amount of oxygen began to increase. Eventually, the air contained so much oxygen, the ozone layer was created. At great height oxygen molecules are broken apart under the influence of the sun's ultraviolet radiation. These oxygen molecules form together to create the ozone. A thick layer of ozone exists at a height of between 15 and 35 kilometers. This layer ensures that the harmful radiation of the sun does not reach the earth. The thicker the ozone layer, the less harmful ultraviolet radiation can reach the earth. Before this protective mantel developed, animals had primarily used water to protect themselves. Consequently, plants and animals could now start to live on the land. The first plants grew on land in the Silurian (about 450 million years ago). These were vascular plants, such as ferns. Several sorts of invertebrates emerged very quickly. In the Devonian, amphibians came into being, and in the Carboniferous, reptiles. On the barrier of the Triad and the Jura (200 million years ago) mammals first came into existence and finally birds. Mammals would fulfill a dominant role after the extinction of the dinosaurs at the end of the Cretaceous period (65 million years ago).