deep time

If we assume that, on average, humans produce a new generation approximately every 20 years, then five human generations equate to a century, 50 generations to a millenium and 500 generations, or 10 millenia, takes us back to the end of the last Ice Age and the dawn of civilization. If we step up a scale and use the entire length of human civilization as our basic unit, then we need at least 100 of these (50,000 human generations) just to reach back a million years. This means that to rturn to the last moment in time when pterosaurs existed - the final days of the Mesozoic, 65 million years ago - one would have to experience a time span equivalent to the whole of human civilization repeated 6,500 times, which is equivalent to about 3 million human generations.

For pterosaurs, however, this was the end of what had already been a stupendously long history. At this, their final moment on Earth, they had been around (or rather above) for more than 150 million years, having first appeared at least 215 million years ago. Or, to try to frame this in a human context, pterosaurs lived, died and evolved for a period equivalent to more than 15,000 human civilizations. This also means, rather surprisingly, that the last pterosaurs existed much closer to us in time than their earliest ancestors.


- The Pterosaurs from Deep Time, by David M Unwin