And to add to that - if there were a large crack in the earth it probably would leave large basalt flows - there are a few of those around and if they didn't go all the way around the globe, then the chances of such a thing are nill.

I'm talking about places like Deccan traps (65mya) and the Columbia plateau (17-15mya) and Siberian Traps (250mya). Could these flows be as a result of an asteroid hit? The timing at the Deccan Traps sure leads one to think about a connection. Even though the asteroid hit over in the Yucatan area, it could be something like those far-field aftershocks... An awful lot of energy is produced when as asteroid hits... I also tend to think that might be an answer for the generation (or start) of a 'hot spot' but its hard to tell when in an area like Hawaii any evidence has long been subducted.

I have never been to the Columbia Plateau but it is on my wish list.

Canie