A few days ago I was reading an article on the discovery channel site about the discovery of large tree fossils in the Antarctic. How is this possible I wonder, that trees could survive in a latitude where there is NO sunlight at all for half the year. It reminded me of a theory put forth by Einstein and others that would also explain the ice ages of the earth. The theory is one of 'crustal displacement' caused by the build up of mass (in the form of ice) at the poles - which eventually caused a centrifugal shift in the lithosphere relative to the earth's semi-solid mantle. Could it be that antarctica has gone through a cycle of shifting in latitude over the past hundreds of millions of years??? http://dsc.discovery.com/news/briefs/20041101/leaves.html
The theory was not put forward by Einstein. If I am not mistaken, Einstein wrote a preface for Charles Hapgood's book. Einstein was not a geologist, yet proponents of this absurd theory will quote him again and again. Charles Hapgood was not a geologist either. One reason I think that this theory is absurd is because it disregards palaeomagnetic data (although, to be fair, I'm not sure that this was available to Hapgood at the time of writing). The main reason, though, is the infeasibility of moving the entire lithosphere as a single unit. The lithosphere consists of the crust and that part of the upper mantle which behaves as a brittle solid. Beneath the lithosphere is the aesthenosphere, which many people mistakenly think is molten rock. In reality, it is a ductile solid, with molten material making up about five percent. Over geological timescales it can 'flow' by deforming plastically. The aesthenosphere is not defined by a smooth surface, as the base of the lithosphere varies in depth by around 100 kilometres. Relatively cold, brittle slabs of subducting lithosphere also intrude down into the mantle to depths of many hundreds of kilometres. Supporters of this theory would have you believe that the crust can slip hundreds of kilometres in a geological instant. Unless they postulate a globally uniform slip surface at some arbitrary depth in the crust, this must also involve the movement of these subducting plates. Instantaneously. Through hundreds of kilometres of solid rock. The theory is also not supported by hot-spot trails, such as the Emperor Seamounts. These mark the path of the plate over a (presumably) static mantle plume. As the article you linked to says, the Glossopteris plants lived in the Permian period, when the Antarctic continent was a lot closer to the equator. They have been moved to their current location not by some sudden, cataclysmic shift, but by the slow and steady jostling of the plates.
Excellent commentary there Laika! I looked up a map of the geological ages and realized that Antarctica has indeed changed latitude and moved further south through plate shifting over endless eons. The article I linked seems to ignore this shift and states that these trees somehow were able to live without sunlight for half the year. Please Register or Log in to view the hidden image!
Oh wait...I just noticed that according to the map I posted, its actually Africa that has moved much further north than antartica has moved south, so even though they are further apart, antartica itself doesn't seem to have ever been in a high enough latitude - remaining south of 60 degrees from the earliest times???
Please excuse me. This is a classic case of me starting a rant off the top of my head before I've actually researched at all. You're right - it does look like Antarctica has been at high latitudes since the Permian. It's been much longer since the continent was at low latitudes. I still stand entirely by my argument against whole crustal displacement.
Although that ECD theory is definitely refuted, I believe it was not about paleaomagnetics. As the magnetic poles wander around even outside the pole circle like the south pole right now, the geographic poles could easily have displaced a few degrees without paleaomagnetics even noticing it. The main rebuting I think was in the alignment of volcanic hot spots, Hawaii, Iceland, Canaries, etc, If you believe that hot spots originate from below the lithosphere then an ECD would carry away the source of the volcanism. Despite all that noise of that ECD being so deeply flawed, I wonder why nobody ever has published a study about the correlation between increased tectonic activity and the 100 ky cycle of the late Pleistocene.
I was under the impression that 'hot spots' were simply 'thin spots' in the lithosphere, in which case it wouldn't matter where they were, relative to the mantle.
Here is a balanced rebuttal which mentions hotspots too: But this is apart of all kind of other hypotheses about hot spots.
Modern deciduous trees essencialy live for half the year in zero light- they shed their leaves each autumn and can't photosynthesise again until spring. I wonder if this seasonality actually developed as a consequence of these early trees living so near the pole. The hotspot debate at the moment is certainly an interesting one. If anyone wants to explore alternative theories I reccommend www.mantleplumes.org
Even if hotspots turn out to have a lithospheric origin, the whole crustal displacement theory is refuted by the detectable presence of sections of lithosphere penetrating the mantle at subduction zones. These are delineated by seismic tomography and earthquake first motion seismic studies. If the crustal displacement theory was correct, I would expect many small sections of subducted lithosphere to be detected under locations unrelated to subduction zones. Perhaps there have been... I don't know.
Well, according to this site anyway, the continent has indeed moved very far south from more temperate latitudes: http://www2.corvallis.k12.or.us/chs/departments/science/marine/Antarctic/Pages/history.html Its hard to imagine how they were even able to find any fossil-bearing rock... under all that desolation. At the Mountains of Madness: Please Register or Log in to view the hidden image!
Yes Please Register or Log in to view the hidden image! There's a theory that that is exactly what happened - deciduous trees originally evolved in polar regions during the Cretaceous (when the whole world was much warmer and there were no ice caps even at the poles) and their leaf shedding is a response to the dark polar winters. There is no reason whatsoever why plants cannot live at the poles. Other than the fact it's too cold Please Register or Log in to view the hidden image! And as for Antarctica, well there's a good account of the past few million years here
