The term ice age was first applied in 1837 by the botanist Karl Schimper (following the proposition of theories by, among others, the Swiss civil engineer Ignace Venetz in 1821 and the Swiss naturalist Louis Agassiz in 1837 in contrast to the held belief that the rocks and sediment left behind were caused by the biblical flood) to refer to a period of glaciation occurring in the Earth' s history, but is particularly applied to that in the Pleistoceneepoch, immediately preceding historic times when an ice sheet spread over northern Europe, leaving its remains as far south as Switzerland. There were several glacial advances separated by interglacial stages during which the ice melted and temperatures were higher than today. There were once thought to have been only three or four glacial advances, but recently it has been discovered that about twenty major incidences have occurred during earth's history. Other ice ages have occurred throughout geological time: there were four in the Precambrian era, one in the Ordovician, and one at the end of the Carboniferous and beginning of the Permian. The occurrence of an ice age is governed by a combination of factors known as the Milankovitch hypothesis: firstly, the Earth's change of attitude in relation to the Sun; and secondly the 92,000-year cycle of eccentricity in the earth's orbit around the Sun, changing it from an elliptical to a near circular orbit, the severest period of an ice age coinciding with the approach to circularity. Research Ice Age
In geology, the Carboniferous was the seventh geological period, 250,000,000 years ago. This era marked the formation of the coal beds. It is the great group of strata which lie between the Old Red Sandstone below and the Permian or Dyas formation above, and is named from the quantities of coal, shale, and other carbonaceous matter contained in them. They include the coal measures, millstone grit, and mountain limestone, the first being uppermost and containing the chief coal-fields that are worked. Iron-ore, limestone, clay, and building-stone are also yielded abundantly by the carboniferous strata which are found in many parts of the world often covering large areas. The thickness of the coal measures in South Wales has been estimated at 10,000 to 13,000 feet. As coal consists essentially of metamorphosed vegetable matter, fossil plants are very numerous in the carboniferous rocks, more than 1500 species of them having been named, a large proportion of which are ferns, tree, lycopods and large horse-tail like plants. The animals include insects, scorpions, amphibians, numerous corals, crinoids, molluscs, cephalopoda, sharks and other fishes. Research Carboniferous
The trias is the formation situated between the Permian and Lias, and so named by the Germans, because it consists of three series of strata, which are called in German the Bunter Sandstein, Muschelkalk, and Keuper. Research Trias
Abbreviations
Research Ice Age
