A TIMELINE FOR THE PLANET click for Home page

The great Varangerian Ice Age

The Varangerian was a terrible series of ice ages that occurred around 700 million years ago (or possibly later) and lasted nearly 200 million years. Some geologists reckon that the entire planet froze over for lengthy periods and life very nearly died out.

I’ve read of compelling geological evidence for this view. But other geologists have put forward evidence that things didn’t get nearly as bad as that.

And there’s palaeontological (fossil) evidence that, in some places anyway, life sailed through almost unscathed (more)

The important thing however is this. Something pretty dreadful certainly happened at that time, even if we can’t say exactly how dreadful.

I doubt whether the two camps differ much on the basics of what happened. The argument is probably over how bad things got before plate tectonics came to the rescue.

This diagram comes from a rather old New Scientist article (6.11.99). It depicts a catastrophic ‘positive feedback’ event. Note that the continents were all sitting around the Equator at the time. This may have had something to do with why the event was so catastrophic

Something caused a reduction in atmospheric carbon dioxide. The ancient supercontinent of Rodinia was breaking up at the time, which will have led to there being much more coastline. I’ve read that organic matter – carbon – gets buried rapidly around coastlines, leaving less for the atomosphere. This cooled the planet, and the polar oceans started to freeze over. The ice reflected much sunlight back into space, cooling the planet further, and encouraging more ice to form. And so it went on until, according to some scientist, almost the entire planet eventually froze over, and life almost died out.

However, as we’ve hinted, the plate tectonic processes carried on regardless. They continued to power the volcanoes. And the volcanoes gave succour to populations of bacteria and algae. It seems that there was no ‘weather’ – no rainfall, no evaporation and no weathering of rocks. So the carbon dioxide that was still spewing out of the volcanoes began to build up in the atmosphere.

Eventually the positive feedback process flipped. The temperature soared, the ice retreated back to the poles, and the temperature soared even further. I’m not clear why the rise in temperature should have been so catastrophically quick. But I’ve read articles with convincing-sounding evidence that it really was.

And apparently this entire cycle repeated itself 3 or 4 times over, as we’ve said, nearly 200 million years.

Eventually however some of the continents moved away from the Equator. This appears to have broken the cycle (no I can’t explain why) and conditions gradually returned to normal.

But of course much of the planet, or even very nearly all of it, had been wiped clean of all life. This left vast niches for the strains of bacteria, algae and emerging animals that had survived to expand into. As we saw earlier, opinions differ on how many of these there were.

And it was only to be expected that new lifeforms that emerged took an entirely different turn.

It was shortly after the end of the ice ages that the first decent sized fossils appear. This is surely significant too. Hard times seem generally to inspire rapid change. It seems that this particular trauma taught Life that Big is Beautiful.