Quaternary
From 2 million years ago to today
The beginning of the new Era (Quaternary Era, or Quaternary) already presents the symptoms of what will be the most striking and dramatic phenomenon of the last 2 million years, the glaciation.
Scientists have long questioned and questioned the Earth for clues or testimonies about the reason for this glaciation. Many hypotheses have been formulated when it was not yet known that the phenomenon of glaciations is a bit of a "recurring motif" in the history of the planet. It has long been thought that this glaciation was the glaciation.
Today we know that this does not correspond to reality.
Considering the phenomenon exceptional, unique, scientists in the past proposed explanations that required exceptional events. It has been said (and written) that the phenomenon was due to profound alterations in the way the planet rotates (an angular displacement of the rotation axis). The large drop in temperature has been attributed to a sequence of "oscillations" in the flow of energy provided by the Sun.
In reality today no one denies that even astronomical phenomena have had a certain weight in the general picture: even meteor showers or asteroid falls (the same events called into question to "explain" the extinction of the dinosaurs) may have occurred.
However, greater weight is given to the interpretation of previous glaciations. In most cases, glaciations occurred when large continental masses were concentrated in the polar regions. The coincidence does not seem accidental. On these masses large accumulations of snow and ice formed, giving rise to "cold" deposits of impressive size. Recall that today 99% of the existing ice on Earth is concentrated on Antarctica and Greenland, the two largest land areas close to the polar regions.
If the polar regions correspond to areas without land, the ice caps form less thick layers, therefore less voluminous: a greater recycling of water is possible, thaws can be more frequent, the ice blocks shatter and the water becomes liquid again (this is what happens today in the North Pole pack). Perhaps astronomical phenomena or other elements not yet fully understood can explain a series of "accessory" events of the glaciation.
These are the recurring thaw periods that allow to distinguish cold (glacial) and milder climate (interglacial) phases during the glaciation. There is no lack of evidence on the periodic retreat of the ice in the glaciations of the past, but they are not always easy to interpret. It is probable that the alternation of glacials and interglacials also occurred in the most ancient glaciations. At this point, in order not to get lost in the sea of numerous hypotheses, we should limit ourselves to the news. It is a chronicle that we can write quite well because the "facts" are, after all, very recent (in geological terms).
Pleistocene: glacial and interglacial
During the glacial period, the thickness of the ice caps may have been in some places over 3 km. The mass of frozen waters was enormous: the sea level therefore lowered and several areas emerged.
Among these:
- the connection between East Asia and North America
- the Isthmus of Panama
- many "land bridges" between the islands of Indonesia
Animal migrations, again possible, were many, as a response to environmental changes.
Obviously the conifers, "pushed" by the advancing ice caps, moved southwards, taking away space for other plants, thus altering the ecology of large areas. The climate was probably cold and rather dry in the temperate belts. The humidity was concentrated in the equatorial zone and partly in the adjacent tropical zones where rainfall was abundant (rainy periods, especially in Africa).
About 1 million years ago there were the first cold waves. The first Donan glacial occurs in several stages. A first interglacial follows.
New glacial: Gùnz
The names of the glacials, for the Alpine region and Europe in general, are taken from those of the Danube, Donau, and some of its tributaries, in whose valleys traces of glacier activity were found.
Interglacial Gùnz-Mindel
Glacial Mindet Interglacial Mindel-Riss. Glacial Riss. Interglacial Riss-Wùrm. Glacial Wùrm.
This glacial (the last, for now) lasted from about 80,000-70,000 years ago to about 12,000-10,000 years ago. The glacial beginning of the Quaternary and ends in the Pleistocene. It follows, with the last interglacial, the Holocene period, in which we are living now. What were the "winning" adaptations?
In some cases the reduction in size (for many rodents, such as mice and similar forms, the salvation was given by being able to be satisfied with little food): but in other cases the solution was given by the opposite trend. Larger animals could cope better with adverse climatic conditions, could eat a lot, accumulate fat or other reserve substances and then face even difficult times.
Thus there were gigantic forms in many orders:
- proboscideans (mastodons, mammoths)
- artiodactyls (deer, cattle)
- rodents (giant beavers)
- perissodactyls (rhinoceros Elasrnotherium, with a 2 m long "horn", a 1 m skull and a body overall more than 6 m long)
Also among the primates there was a giant: the Gigantopithectis Pongid, 3 meters tall.
All mammals developed thick furs. Let's not forget that, in the Pleistocene, no matter how cold the climate was, there was always an alternation of the seasons: there were still summers with a certain luxuriance of vegetation, albeit in very limited areas.
During the glacial periods there were intense migrations: the animals of the temperate zones moved several times from South to North and vice versa, crossing the equatorial regions.
Thus, for example, megaters and glytodons reached North America. In some isolated environments with particular characteristics, faunas developed in which there were forms of medium or small size derived from others, present elsewhere, of large or gigantic size. The ecological roles of these dwarf animals were roughly the same as that of large species. In Sicily (Italy), for example, during the interglacials, tiny deer developed, a megatherium as large as a cat and the famous dwarf elephants (Palaeoloxodon falconeri) only 90 cm tall at the shoulder. Even in the islands off the coast of Indonesia and in the Celebes group there were dwarf elephants, while in Santa Barbara, California, small woolly mammoths lived.
While large mammals gave smaller and smaller shapes, some of modest size, thanks to isolation, produced giant shapes instead. Dormice and rats of considerable size were found, for example, in various islands of the Mediterranean: an obvious "answer" to the abundance of food and the lack of predators.
