he 'reindeer' cave art we saw in chapter 8 was located in southern France and there are certainly no reindeer there now. Reindeer are caribou, a sub-arctic animal. So as the big-brained human-like fossils go back some 300,000 years perhaps we should look at what our scientists tell us about the last ice age and its ending.

No one seems to know why it ended when it did; in fact there are various theories about how and why ice ages come and go. It has been recognized that oxygen isotope ratios vary with the volume of glacial ice. The earth also has magnetic field reversals from time to time, which can be identified. By taking deep sea cores and checking the oxygen isotope fluctuations against the magnetic polarity reversals, we get this:

I prefer to read the scale horizontally as shown here, although it was originally vertical. Our present time is now at the right. Warm is up, cold is down. The horizontal time span is almost 2 million years. You can see that we are now reaching a peak of temperature after a climb from the last ice age. That climb is longer than any other in the last 1.9 million years, which suggests we are in for falling temperatures towards another ice age fairly soon. Temperatures have on average been in decline over the last 300,000 years. We can also note that the swings between warm and cold spells are becoming much more severe than they were earlier in the last two million years or so. Present conventional wisdom tells us the last ice age ended about 10,000 BP or at most started its decline about 12,000 years ago. If so, this chart may be of limited value unless the 10-12,000 BP change was too small or too recent to register, because by actual measurement it appears to me from the time scale given that the low point occurred at just over 30,000 BP and temperature has been rising since then.

As the interglacial ages advance, the amount of water in the oceans and elsewhere becomes correspondingly greater, producing a terraced effect, like this:

When the ice increases the sea levels go back down.

What this means is that as the planet is at present in a warm spell with sea levels rising, much low lying land is flooded that was inhabited during or soon after the end of the last ice age. Even Roman docks and wharves in the Mediterranean can be seen under water today. Land also rises when the weight of ice melts off it, and continents are always drifting about. So our planet has plenty of change and surface movement.

When we consider the time scale of ice ages against the known specimens of big-brained individuals, say back to about 300,000 years ago, we see they can be traced to the peak of a warm period and their history since then has spanned three ice ages and three warm periods. But during all that time it is apparently only in the last 5,000 to 6,000 or so years that urban civilizations have arisen.