Global cooling.
Folding of the Sierras and Rockies.
Rise of anthropoids...

Timeline 6 - 25 million years ago to present

www.fsnielsen.com - return to graphic - previous - next - 

The Miocene is the next to the last geological age before our time. It is the age of the last - American - wave of mountain folding, and of steadily cooling global climates. More and more devastatingly and violently, great ice-ages are plying their way across the surface of the Earth. Nevertheless, the adaptive and intelligent mammals are thriving, particularly in the short interludes between glaciations; producing new species (the grazing animals) that will later play a key role in human history. And among the mammals, the most adaptive and intelligent of all, the anthropoids, are also thriving. They are the distant ancestors of human beings.

The violent conditions under which these species developed may be seen from the two graphs displayed below. They cover the last 2 and 1 million years respectively (i.e. the Miocene as such has by now already passed, and glaciations have become still more intense) but they may probably - at least for our purposes - be seen as fairly typical of the latter, more intensely glaciated period of the 25 million years that are covered by my present timeline.

Source: http://www.carleton.ca/~tpatters/teaching/climatechange/glacial/glacial2.html	Source: http://www.bom.gov.au/info/climate/change/gallery/17.shtml

The two graphs (one of which has been inverted, to show time in the same direction!) demonstrate several notable things:

• First, temperatures fluctuate strongly throughout the period. The schematic markings on the timelines do not in any way do justice to the complexity of the changes involved.
   
• Secondly, we are at present living in a truly remarkable age. The temperatures we consider "normal" are in fact highly atypical, much colder conditions being the rule, even during interglacials. (The line marked "0" on the right graph corresponds to the temperature we at present enjoy.) Indeed, judging from the right graph alone, one might be tempted to conclude that the last two interglacials - with their unusually high temperatures - indicate that global temperatures are on the rise. The left graph, however, dispells this impression. 1.7 million years ago, interglacials were quite as warm as today, and the glacial periods were not nearly as cold. If anything, temperature fluctuations during the last million years or so, seem to have become more violent.
   
• Third, we gain a new perspective on human history. Homo sapiens sapiens originated about 130,000 years ago, that is some time before the "last interglacial" marked on the graph to the right. In contrast, the history of the anthropoids, the first distinguishable ancestors of human beings, goes back some 30 million years, to when the first anthropoids evolved in Africa, from which they spread to Asia and evolved a number of new species, until Australopithecus Afarensis, a tool-using, bipedal anthropoid (known to us by the fossilized remains of a female of the species called "Lucy" by her finder) appeared, once again in Africa, a mere 3.5 million years ago. At the time it was only 3.37 million years until human history would begin.
   
• Fourth, the spectacular speed of anthropoid evolution is no doubt a reflection of the efficiency of the "evolutionary pump" of constantly alternating glacial, semi-glacial and interglacial conditions. Multiplying and spreading out during the interglacials, the anthropoids were stressed to evolve biological responses to dramatic reductions in and changes of their habitat.
   
• Fifth, and finally, homo sapiens sapiens evolved under glacial conditions and is more fundamentally adapted to glacial hardship than to the interglacial luxury of our day. The implications of this for our understanding of human beings and human society are not at all clear.

With this timeline, we are approaching conditions similar to our own age. But "our age" proper, the age of human history, the age of agriculture, cities and writing, is still only a thin red line (drawn too wide on the timeline) at the bottom right corner of the timeline.