It is time for ice!
Older ice ages
The best kept traces of the glaciations can be found on the southern continents, which altogether formed Gondwana during the Perm and the Carboniferous periods. Only few sediments from the ice ages are known from the Devonian and the Silurian periods. Unfortunately, the traces which stem from the Ordovician (505 to 438 million years ago) and the Cambrian (590 to 505 years ago), are not reliable enough to point out on which scale the glaciers occurred. In contrast, many traces have been found from the era earlier than 600 million years ago. From those traces, one can derive that primarily North-America, Norway, the British islands and other northern islands were harmed by the ice. Land ice has been quite normal during the earth’s history. However, during the main era, the Mesozoic, which consisted of the Triad, Jura and Cretaceous periods, and lasted from 225 until 65 million years ago, there were barely any ice ages. It was an era during which many sorts, among which reptiles, dinosaurs, ammonites, fish, mammals, birds and broad-leaved trees, flourished in numbers and variety.
Ice ages in the Netherlands
During the Pleistocene (1.8 million years ago until 10.000 years ago), the Netherlands was partly covered with ice on two occasions. Both happened during the Elsterene and the Saline. The land ice came up from the north during the Saline and completely reshaped the scenery. The land ice continued until the Haarlem-Nijmegen boundary. Parts of the lateral moraines that were created then are still visible today. The hills in the surroundings of Nijmegen or in the ‘Veluwe’ are examples of this. You can also find many traces in the scenery of Drenthe. The characteristic megaliths are built from the stones that were imported during the ice ages.
In the last two hundred years, many theories have been put forward to try to explain the ice ages. These theories need to meet two demands. Firstly, they need to explain why ice ages can emerge and vanish so quickly. Secondly, they need to explain why there were some periods where the ice ages alternated, and why there were periods when barely any ice ages existed. In the 19th century it was already thought that ice ages could have extraterrestrial causes. During the 20th century, scientists got more and more techniques to carry out extensive and thorough research. The influence of structural astronomical factors, such as the distance between the sun and the earth, were proved in the 1970s. At the same time, further knowledge was gained about climate changes in general, through the CLIMAP-research. Much is still unknown about the causes of ice ages. The sun activity could for instance have increased or decreased temporally. Also, the amount of clouds could have influenced the reflection of the sunlight. Finally, it is possible that the atmospheric content of carbon dioxide and ash, due to volcanic activity, could have caused small changes.