[yeahbut]

A little help would be appreciated from all you well read, well rounded, well informed Peakoil contributers...no, but seriously, I've just been reading the first few chapters of Richard Manning's "Against the Grain- how agriculture has hijacked civilization"(recommended by a Peakoiler, can't remember who). I was finding it fascinating, and convincing, til I got to this remarkable passage:

"On this planet, glaciation is not the exception but the norm. Over the last billion years or so, a regular cycle has governed the earth, characterized by glaciations lasting sixty to ninety thousand years, interrupted by brief interglacials of roughly ten thousand years."

Now, I'm no expert on the climatic and geological history of our planet, but I've done enough reading over the years to gain the distinct impression that the general consensus is rather different from Manning's summary. About exactly the opposite different in fact- glaciation is not the norm, but the exception. For most of our planet's history there was no polar ice at all. There have been four ice ages in the 4.5 billion years since earth was formed, and the ice age we find ourselves in right now only got going properly about 3 million years ago. That 3 million years has been characterized by glacial and interglacial cycles. The previous billion certainly was not.

Does that sound about right? Is it possible that Manning got it that wrong? If so, how can a guy who I've heard name-checked a lot over the years, and quite a few times here, be taken seriously? I'm kinda hoping someone will explain to me how I've got it all wrong, cos I was enjoying the book so much. If I'm not wrong, I really don't think I'll read anymore. If his understanding of the world(and basic research!)is that poor, I don't see why I should take seriously anything else he has to say. So, help me out with my ultra-geeky problem here, willya?

[Opies]

No actually he is quite correct. I've heard from numerous sources that glaciation and ice ages happen almost like clockwork. In fact, I recently learned in an earth sciences class that at one point our planet was a giant snowball. because of this the surface has a very high albedo in the 80-90% range, and the snow becomes like a giant mirror and the sunlight can't gain enough ground to melt the snow. At this point it would be considered a dead planet, but I believe our geologic activity saved us in one way or another... maybe something about volcanoes.

Either way, I do believe and have had it confirmed multiple times that glaciation is a regular event, not an exceptional one. I could always be wrong though, I'm no expert on the topic and what I've heard has always been second hand research.

[katkinkate]

I think he's confused on this point. The last glaciation period of a bit under 50 million years (MY) is the pattern he said. Before then was the extended period of warm which the dinosaurs dominated till 65 MYA. There were earlier periods of ice age, alternating with long warm periods, but the fine patterns are more difficult to figure the further back you go, so I don't think you can assume they were manifesting the same pattern of glaciation/ interglaciation as this latest one. I found this nice graph showing the last 500 MY in Wikipedia.

That being said, glaciation itself is not necessarily more common than warm periods, but it is one of the normal states of the planet and will likely happen again.

[Novus]

There have actually been a few super glaciations in the times before the Dinos when glaciers came all the way down to the equator.

[yeahbut]

$this->bbcode_second_pass_quote('Novus', 'T')here have actually been a few super glaciations in the times before the Dinos when glaciers came all the way down to the equator.