So I was staring idly at a globe the other day, and I happened to wonder: why is the majority of the land mass in the northern hemisphere? North America and Eurasisa are entirely north of the equator, and good portions of Africa and South America are as well. There’s almost a circumpolar ocean around Antarctica.
Just a fluke? or is there something about the drift mechanism that bunched them towards the north? And does having the majority of the land mass in one hemisphere affect rotation of the earth or anything?
Gondwanaland (the single continent) used to be in the southern hemisphere but once it split up the continents drifted northward. I think that’s because north is actually the bottom of the Earth, not the top, as Northern cartographers were wont to mistake.
The continents have wandered about quite a lot in Earth history, so the current distribution is nothing special. This page has links to some animations so that you can see just how much things have changed over the past 750 million years.
Since the continents represent a very thin shell “floating” on the mantle, it doesn’t seem as though their distribution per se has any major impact on the Earth’s rotation, etc. Density anomalies down in the mantle, however, may be enough to disrupt the Earth’s moment of inertia, resulting in rotational instability and ultimately a realignment of the Earth’s rotational axis (a phenomenon called true polar wander). The density anomalies in the mantle may be related to movement of the plates in the crust (e.g., a broken-off piece of subducted crust), but not necessarily (e.g., large mantle plumes of molten rock that originate near the core-mantle boundary).
The whole issue of true polar wander is kind of contentious in and of itself. Geologists accept that it does happen slowly on long timescales (tens to hundred of millions of years), but there have been claims for very rapid motion, e.g., 90 degree shift in magnetic pole position with respect to the crust in just a few million years. With the exception of a true polar wander event around 84 million years ago, most of these claims for rapid plate motion are not well supported by the available data.
For many years, it was believed that some vast Terra Australis must balance out the mass of Eurasia and N America, and finally, the Royal Society sent Capt Cook out to go find it. He wound up sailing all over the Pacific- from New Zealand to the Aleutians (he was up there trying to find the Northwest passage from the other side- he got sent on all the goose chases) and a lot of places in between on his three voyages in the 1770s. For a fascinating read about these incredible feats, check out Tony Horwitz’s Blue Latitudes.
As for why the continents are unbalanced, I’d say it’s just a fluke. Whether it affects the rotation of the earth is hard to say. Continental crust isn’t as dense as oceanic crust, but it’s also thicker. But compared to the rest of the planet, neither is much to shout about. Density anomalies in the mantle would be more important, as sunfish points out.
He’s saying it’s us notherners who are wrong in thinking the north pole is the top of the world. He contends that the north pole is the bottom and all the crappy continents are sinking downwards.
Of course the North Pole is the top and the best continents have floated upwards.
